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مدیر وبلاگ : pc7a
نویسندگان
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negative conductor is connected to the structure to be protected and the positive conductor is connected to the anodes at the power source output terminals.
Caution: The negative lead of the rectifier must be attached to the structure to be protected. If the structure is mistakenly attached to the positive lead, it will serve as an anode and rapid corrosion failure can result.
6.2.2.21 The transformer/rectifier shall be connected into either the existing earthing circuit or shall be separately earthed to a new earthing system according to design specifications. Typical installation of earthing system for cathodic protection station with fencing illustrated in standard drawing No. IPS-D-TP-717.
6.2.2.22 When the metal work of the transformer/rectifier unit is bonded to earthing terminal, precautions shall be taken to ensure that there is no possibility of metallic connection, even for a short period, between the earthing system and the groundbed of the cathodic protection installation.
6.2.2.23 After erection of a unit, it is important that the following be checked:
a) Oil level is correct, if the unit is oil cooled.
b) Fuse ratings are correct.
c) Input and output cables are properly identified prior to connection to the electricity supply.
6.2.2.24 Transformer/rectifier(s) shall not be energized until all check-out and commissioning tests have been completed (see 11).
Note:
When electricity is connected, correct polarity and groundbed resistance should be verified by energizing the unit.
6.2.3 Cabling (see relevant IPS-D-TP Standard drawings)
6.2.3.1 All cabling shall be routed and installed in accordance with the design drawings and to the approval of the engineer.
Sufficient information is given in the design drawings to indicate the general routes of cables. Final route are to be determined on site and changes made only where absolutely necessary and with the approval of the Engineer.
6.2.3.2 Cables for connection between the transformer/rectifier and pipe and groundbed shall conform to the dimensions and characteristics indicated in the drawings and/or materials specifications (see IPS-M-TP-750: Part 7).
6.2.3.3 Cables run between the groundbed and transformer/rectifier and between the transformer/rectifier and structure(s) shall be continuous and free of splices.
6.2.3.4 To avoid kinks and knots, all cables shall be carefully unreeled and laid directly into the prepared trench. Where cables are reeled on drums, the drums shall be mounted on jacks.
6.2.3.5 Trenches shall be kept away from buried pipes containing hot fluids and from pipes liable to temperature rise owing to steaming out.
6.2.3.6 The bottom of the trench receiving direct buried cable shall be relatively smooth, undisturbed and well tamped earth. Care shall be taken to be sure that there are no sharp rocks or other objects in the cable trench bottom that could damage cable insulation.
6.2.3.7 Cables shall be laid with sufficient "Slack" to avoid breaking during or after backfilling and to allow for shifting and settling. When connection are made to pipe, the cable shall be wrapped around the pipe twice and taped down. Each wire terminated in the test box shall have at least 15 cm of slack coiled.
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6.2.3.8 Cable runs under roads and areas subject to vehicular traffic shall be installed in steel or aluminum conduit of 20 mm minimum size.
The conduit used shall be reamed carefully after cutting to length to remove all sharp edges. Bushings shall be installed on both ends of the conduit.
6.2.3.9 The positive cable anode lead is especially critical to the operation of the system. It is imperative that insulation remain intact. Extreme care shall be taken to ensure that the entire cable and all connections are waterproof. Care shall be taken to ensure that there are no short circuits between the positive cable and the structure or conduit.
6.2.3.10 Cables shall enter the rectifier, groundbed test box and where applicable, other enclosures, in properly sized rigid conduit extending 450 mm below ground surface. Plastic inserts shall be used in conduit ends to protect cable.
6.2.3.11 Cables shall be installed as follows:
- Cables shall be laid in prepared trenches.
- Before cables are placed, the trench bottom shall be leveled and backfilled with a layer of soft sand 10 cm thickness.
- This soft sand shall be leveled and the cable placed thereon. The laying of cables shall be carefully done to avoid any damage to insulation. After laying and before covering, all cables shall be examined for cuts, nicks and any other damage. All damaged cables must be repaired before burying.
- The cable shall then be covered with a layer of fine sand 20 cm deep. The sand shall be lightly tamped. Machine compaction shall not be used.
- A protective covering warning device (bricks, tiles or red concrete slab) shall then be applied. The protective covering shall be placed without disturbing the sand fill while pouring.
- The remainder of the trench shall then be backfilled and compacted with soil such that existing elevations are met.
6.2.3.12 All cable main runs shall be tagged at each end with waterproof identification tags as per cable schedules. Tagging method shall be approved by engineer prior to being carried out.
Color code of the cables shall be as follows:
Between T/R and positive test box : Red
Between T/R and negative test box: Black
Between positive test box and groundbed: Red
Between negative test box and structure: Black
Between test point and pipeline: Black
Between test point and casing: Red
Between test point and foreign line: Red
Between test point and insulating joint/flange: Red
6.2.3.13 All cable runs shall be identified with cable markers of the type shown in the IPS-D-TP Standard drawings, installed at fifty (50) meter intervals and turning points. Markers shall be installed at one edge of the trench.
The following information shall be marked on each marker plate, with a steel die stamp:
- Direction of cable runs.
- Location of trench with respect to marker.
Plates shall have a blank space approximately 15 mm × 50 mm for company’s use.
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Notes:
1) The distance between the top of a cable and the surface under which it is installed (depth of burial) shall be sufficient to protect the cable from damage imposed by expected surface usage.
2) The top surface of the cable in the trench shall be a minimum of 70 cm below finished grade.
3) Burial depth may be increased where necessary to meet underground conditions.
4) In areas where frost conditions could damage cables, greater burial depths than indicated above may be desirable.
5) Lesser depths than indicated above may be used in rocky terrains. The supplemental protection shall be provided. The supplemental protection should be sufficient to protect the cable from damage imposed by expected surface usage.
6) Where The surface is not to final grade, under which a cable is to be installed, the cable should be placed so as to meet or exceed the requirements indicated above, both at the time of installation and subsequent thereto.
7) The horizontal separation between direct buried cable and other underground structures shall be not less than 300 mm to permit access to and maintenance of either facility without damage to the other.
8) Where a cable crosses under another underground structure, the structure shall be suitably supported to prevent transfer of a harmful load onto the cable system.
9) Where a cable crosses over another underground structure, the cable shall be suitably supported to prevent transfer of a harmful load onto the structure.
10) Adequate support may be provided by installing the facilities with sufficient vertical separation.
11) Adequate vertical separation shall be maintained to permit access to and maintenance of either facility without damage to the other. A vertical separation of 300 mm is, in general, considered adequate but the parties involved may agree to a lesser separation in special cases.
12) Plowing in of cable in soil containing rock or other solid material shall be done in such a manner that the solid material will not damage the cable, either during the plowing operation or afterward.
13) The design of cable plowing equipment and the plowing-in operation shall be such that the cable will not be damaged by bending, side-wall pressure, or excessive cable tension.
14) At low temperatures some plastics are so brittle that they may crack when bending the cable, and therefore no cables shall be installed during freezing weather.
6.2.4 Electrical connections
6.2.4.1 Attaching cables
6.2.4.1.1 The thermit weld process (cad welding) should be used for attaching test leads, and bonding lead wires to structures.
6.2.4.1.2 Thermit welding process shall be such that copper penetration into the pipeline material shall not be deeper than 1 mm and that the hardness shall remain inside the original pipeline requirements.
6.2.4.1.3 Thermit welding shall not be used for austenitic stainless steel and duplex steel pipelines.
6.2.4.1.4 Thermit welding shall not be used for structures contain or have contained flammable or combustible liquid.
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6.2.4.1.5 Thermit welding process shall be applied in accordance with the requirements of Clause 13 and standard drawing No. IPS-D-TP-703.
Notes:
1) Connections of test lead wires to the structure must be installed so that they remain mechanically secure and electrically conductive. Care shall be exercised to ensure that cables and connections are not damaged during backfilling. Sufficient cable slack shall be provided to avoid strain.
2) All cable attachments to structures shall be coated with an electrically insulating material provided or approved by the Company. This coating shall be compatible with the structure coating and cable insulation, and have good adhesion to both.
3) The following welding process, as an alternative to thermit welding, for the cable connections may be required:
3.1 Welding
A metal plate, 50 × 50 mm minimum, provided with a welded M 10 threaded stud bolt, shall be welded to the pipeline by two continuous welds in the circumferential direction of the pipe only. The plate shall be made of the same material as the pipeline.
The cables shall be connected to the threaded studbolt using crimped or brazed cable lugs, nuts and serrated washers.
3.2 Stud welding
Stud welding may be done using an electrical (resistance welding) or mechanical (friction welding) process which shall be approved by the Company.
The stud material and consumables shall be compatible with the pipeline material. The process shall not influence the pipeline material properties to fall outside the original specifications.
The size of threaded studs shall be 8 mm or more to suit the cable size. The cables shall be connected to the stud using crimped or brazed cable lugs, nuts and serrated washers.
3.3 Pinbrazing
The pinbrazing process shall use specially designed cable lugs and brazing pins to braze the cables to the pipeline and shall be approved by the Company.
The brazing materials shall be compatible with the pipeline material. Penetration of copper and/or other brazing metals into the pipeline shall not be deeper than 1 mm and the hardness shall remain inside the original pipeline requirements.
Pinbrazing shall not be used on austenitic stainless steel and duplex stainless steel pipelines.
3.4 Glued connections
Where welding, brazing or thermit welding is not possible, e.g. for safety reasons, the contractor may design glued electrical connections using metal plates bonded with electrically conductive epoxy resin. This method shall not be used for current carrying cables (drain cables, bond cables). The materials to be used and the installation procedure shall be approved by the Company.
6.2.4.2 Splicing cables (see IPS-D-TP-719)
6.2.4.2.1 Cable splicing plays a very important role to a good cathodic protection system. Cable
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splices shall be properly insulated to preclude current leak.
6.2.4.2.2 Anode lead wire to header cable connections and header cable splices shall be made by using a split bolt connector (line tap). An epoxy resin splicing kit shall then be applied over the tightened zero resistance connection in accordance with the manufacturer’s recommendations, 6.2.4.3 and standard drawing No. IPS-D-TP-719.
Notes:
1) For good insulation result, manufacturer’s instruction for epoxy resin splicing kit installation shall be rigidly followed.
2) The resin shall not have exceeded its specified shelf life.
3) Buried connections must be protected with extreme precautions against the entrance of any moisture, for any discharge of current to earth from the cable will destroy it in a matter of days or hours.
4) Proper cleaning (degreasing and abrading) of the insulation is necessary to ensure that a watertight bond is achieved between the insulation and the cable-jointing compound. Where repairs are carried out, a minimum of 50 mm of cable insulation, on each side of the repair, shall be contained within the repair.
5) Random checks shall be made during installation of joints in accordance with the manufacturer’s instructions. Where applicable, these checks should ensure that:
- the joint area is dry;
- the resin compound has not overrun its expiry date;
- sheath abrasion, if specified, is properly carried out;
- the connector stagger and other dimensions are observed;
- the preparation, installation and tightening of conductor connectors is correct;
- the appropriate tools, particularly for compression connectors are used by the installer;
- the cable is laid straight and the box and cable are well supported so that movement during pouring encapsulant is not likely;
- the cold pour encapsulant is thoroughly mixed;
- the encapsulant fills the mold and does not distort its shape significantly;
The electrical testing of the installation is deemed to be completed by final system installation/commissioning tests.
6.2.4.3 Cable jointing procedure
6.2.4.3.1 General
a) The instructions and procedures given in this Clause should be observed at all times during the preparation and installation of a cable joint.
b) Joint kits should be inspected before use and any defect made good.
c) When using resin compounds good housekeeping practices should at all times be observed in accordance with manufacturer’s instructions. The following precautions should be taken when handling jointing materials used in the preparation of cable joints.
- Do not use in a confined unventilated area.
- Avoid breathing the vapors.
- Wear protective clothing at all times when handling cold pour resins.
- Avoid contact with the skin and eyes.
Note:
In case of accidental contact with skin, treat the affected area with copious quantities of water (or with the reaction agent recommended by the resin manufacturer). For eyes, follow the same treatment and immediately obtain medical aid.
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- Containers of resin compounds should be kept closed at all times except when actually in use.
- Smoking should be prohibited.
- Accidental spillage should be cleared immediately.
- After use, all containers should be disposed of strictly in accordance with the manufacturer’s instructions.
d) The following equipment may be required for use:
- a basic jointer’s tool kit including consumable materials;
- a tent or some effective means of protecting the jointing operations from moisture, rain or excessive cold or heat;
- those tools supplied or recommended by the splicing kit manufacturer, e.g. compression tools;
- special equipment, e.g. fire extinguishers and pumps.
e) The equipment used in making cable joints should be regularly maintained in accordance with the manufacturer’s instructions.
f) At all times, every effort should be made to ensure dirt does not become entrapped in a joint. Tools should be laid out in an orderly manner and when not in use replaced in their chosen place. Waste products, e.g. trimmings from sheaths or insulation, should be placed in a receptacle provided for the purpose.
6.2.4.3.2 Jointing application
a) Before starting the joint, the jointer shall ensure that all the correct materials are available.
b) The cables to be joined should be lined up approximately in the position required for the joint.
c) The outer covering(s) of the cable(s) should be removed to the dimensions given in the jointing instructions; followed by removal of other cable materials to expose cores. The core insulation(s) should then be removed or partly removed over sufficient lengths to take the connectors.
d) PVC sheaths should be removed with a sharp knife or special tool designed for the purpose, by making a circumferential cut for cable ends or tow cuts at joint positions, plus one longitudinal cut. The circumferential cut(s) is made first and the PVC is cut through about two-thirds of its thickness to avoid damaging the cable component below the sheath. The longitudinal cut is then made with the knife blade almost tangential to the cable. The PVC sheath is completely penetrated when making this cut. The sheath can then be removed by tearing it away at the circumferential cut(s).
e) Polymeric insulation should be removed with a knife, care being taken not to damage the conductor.
Note:
Polymeric material is easily cut when slightly warm, but care should be taken not to overheat.
f) The conductors and connectors should be cleaned before the connections are made. It is important that the cleaning of conductors should be strictly in accordance with the manufacturer’s instructions.
g) Mechanical connectors should be tightened in accordance with the manufacturer’s instructions.
h) The joint mold should be presented to the joint to ensure adequate clearances. When satisfactory, secure the mold and fill with encapsulating compound where appropriate.
Note:
In low temperature conditions, cold pour compounds can be harder to mix and will have longer curing times. Every effort should be made to store the compound at an ambient temperature above 5°C, and at all times the manufacturer’s storage instructions should be
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observed.
6.2.5 Installation of test stations (test points)
6.2.5.1 The contractor shall install the cathodic protection test points which shall be as indicated in the Standard drawings (see IPS-D-TP-710 & 716). The contractor shall supply the necessary materials for installation of test point when required by the Company.
6.2.5.2 The contractor shall install cathodic protection test points at locations specified in the design drawings. Precise location of test point connections to the structure shall be subject to the engineer’s approval prior to their attachment.
6.2.5.3 Unless specified otherwise by the Company, cathodic protection test facilities shall be installed at distances of maximum 1000 m along the pipeline and at 250 to 300 meters in urban or industrial areas and, in addition, at all foreign pipeline crossings, insulating flanges/joints, cased crossings, both sides of river crossings and at any location where interference with other buried installations is found at the time of starting-up of the cathodic protection system in accordance with the design drawings.
Care shall be exercised to avoid damage to structure coating during excavation and backfill.
6.2.5.4 If pipelines are running in parallel, but not in the same trench, each pipeline shall be provided with separate potential monitoring facilities. Test points shall be installed not more than 2.5 m away from the pipeline.
6.2.5.5 Cables necessary for the connections between structure and test point shall be as specified in the design drawings. Cables shall be laid on padding of soft earth at least ten (10) centimeters thick in trench at least 0.80 meters deep and shall be covered with at least fifteen (15) centimeters of soft earth. Cables shall be so placed that they will not be subject to excessive strain and damage during backfill operation. All test point cables shall be installed with sufficient slack.
6.2.5.6 The structure and test lead wires shall be clean, dry, and free of foreign materials at points of connection when the connections are made. Connections of test lead wires to the structure must be installed so that they will remain mechanically secure and electrically conductive.
6.2.5.7 The test lead connections shall be properly bonded to the structure by thermit-welding process.
6.2.5.8 The thermit-weld on the structure shall be made after installation of the structure. In any case, the contractor shall ensure that the cables are maintained intact. Splicing of the cable shall not be permitted.
6.2.5.9 All test lead wire attachments and all bared test lead wires shall be coated with an electrically insulating material. If the structure is coated, the insulating material shall be compatible with the structures coating and wire insulation.
6.2.5.10 Conductor connections at bonds to other structures or across insulating joints shall be mechanically secure, electrically conductive, and suitably coated. Bond connections shall be accessible for testing.
6.2.5.11 Cathodic protection test points attached to the structure shall be tested for electrical continuity between structure and test connection, prior to commissioning of the cathodic protection system. Any cable not passing the final tests shall be replaced.
6.2.5.12 All test point cable leads shall be color-coded or otherwise fitted with identification tags adjacent to the cable lug. Damage to wire insulation shall be avoided. Test leads shall not be exposed to excessive heat and sunlight.
6.2.5.13 Each test point shall be clearly labeled and/or marked with a specific number as follows:
- For above ground test points by stamping a plate attached to the test point.
- For grade level test points, marker plates shall be installed on the nearest adjacent building or wall in built up areas.
6.2.5.14 Types of test points
Type A - Single test points
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a) Above ground test points for desert or rural area installation. This type shall be installed along the main branch and/or cross country lines in accordances with standard drawing No. IPS-D-TP-710. It utilizes a combined line marker and a terminal box with screw-on cover with test wire coiled and left in the box through conduit with their ends taped to avoid contact.
b) Grade level test points for urban area installation. This type shall be installed in sight-holes (embed into the ground) in the pipeline axis, off limits of road crossings in accordance with standard drawing No. IPS-D-TP-722. It utilizes a street sight-hole with cover with test wires coiled and left in the terminal board. Ample wire slack shall be left in the housing below the terminal panel to allow for backfill settlement and for withdrawing the terminal panel.
Type B - Crossings and parallelism with existing pipelines
This type will consist of two separate cables attached to each individual pipeline, terminating in a test box (type 1) with suitable facilities to install direct or resistive bonds. The cables to each pipeline shall be identified by color coding or tags.
Type C - Casing test point
This type shall be installed in accordance with standard drawing No. IPS-D-TP-716. It utilizes a combined line marker and a terminal box with screw-on cover with test wires coiled and left in the box through conduit with their ends taped to avoid contact and clearly labeled.
If the casing is longer than 30 meters, the test point shall be installed at both ends of the casing. Shorter casings shall be provided with a test point at one end only.
In each test point, one test cable shall be connected to the pipeline and, one test cable shall be connected to the casing. Both cables shall be terminated in test point.
Type D - Insulating joint/flange test point
This type shall be installed across each insulating joint/flange in easily accessible locations. Two cables shall be connected to each side of the joint or flange. All cables shall be separately terminated in common test box (type 1) with suitable facilities to install direct or resistive bonds. The cables to each side of the insulating joint/flange shall be identified by color coding or tags.
Type E - Line current measurement test point
This type shall consist of two pairs of cables, each pair connected to the pipeline 30 to 60 meters apart. All cables shall be separately terminated in common test box (type 1) with suitable facilities. The cables shall be identified by color coding or tags.
6.2.6 Installation of insulating devices
The contractor shall align, install and test all insulating devices shown in the design drawings in accordance with requirements of Clause 12.
6.2.7 Installation of test box(es)
The test box(es) internally equipped with copper bus bar, copper links, copper terminals and a proper rotary resistor shall be installed for the following purposes:
a) Connection of anodic cables (header cable and positive cable) between groundbed and positive pole of transformer/ rectifier, and control of the groundbed current through the rotary resistor circuit (as positive test box).
b) Connection of cathodic cables (negative cables) between structure and negative pole of transformer/rectifier, and control of the cathodic protection system (as negative test box).
c) Bonding between different cathodic circuits.
The box(es) shall be installed in accordance with standard drawings Nos. IPS-D-TP-702 andIPS-D-TP-704.
6.2.8 Earthing of CP equipment
6.2.8.1 The object of electrical earthing is to ensure effective operation of the transformer/rectifier in the event of earth fault current, that might otherwise cause damage to property, and protect against
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danger to life through shock due to installation metal work being maintained at a dangerous potential relative to earth.
6.2.8.2 Local earthing circuit shall be installed at the CP station(s), in accordance with 6.2.8.3 and as detailed on the standard drawing No. IPS-D-TP-717.
Each earthing system will be composed of:
- Earthing pits for connection and inspection of the copper rods.
- Copper rods inserted in the earth.
- Bonding header cables between the pits.
- Earthing cables from header cable to CP equipment and fence.
6.2.8.3 The requirements for the connection of metalworks of CP station(s) are specified in:
BS 7430 (1991) "Code of Practice for Earthing"
Formerly C.P. 1013 (1956)
BS 6651 (1985) "Code of Practice for Protection of Structures Against Lightning"
IPS-E-EL-100/1 "Earthing, Bonding and Lightning Protection"
Notes:
1) Earthing shall be installed fully underground.
2) Earthing should be carried out at locations where the soil resistance is the lowest. Sandy soil should be avoided.
3) The grounding resistance should be kept as low as possible by adding salt, coke or any other kind of backfilling.
6.2.8.4 If CP station(s) to be installed inside the area with individual earthing system, such as compressor station, valve station, city gate station, etc. The CP equipment shall be adequately bonded together and connected to the existing earthing system.
6.2.8.5 In absence of earthing drawings, CP equipment shall be adequately bonded together and connected to the earth electrodes.
6.2.9 Fencing
6.2.9.1 Installation of fencing shall be as follows:
- For transmission pipelines according to IPS-D-TP-709.
- For in-plant and distribution networks that is inside the cities, according to IPS-D-TP-718.
6.2.9.2 Erection of fencing shall be performed by competent workmen, experienced in industrial type fence erection.
6.2.9.3 Contractor shall be responsible for the supply of all material, tools and equipment necessary to carry out the work.
6.2.9.4 Particular care shall be exercised during fence erection so that no underground piping, cable or other appurtenances are touched or damaged.
6.2.9.5 On completion of work, all excess and waste materials resulting from fence construction shall be removed from the site by the contractor.
6.2.10 Parallel power lines
If the pipeline runs in the vicinity of high voltage power lines, the contractor shall investigate whether high ac voltages can be present on the pipeline by induction or otherwise and whether devices have to be installed for protection of the pipeline and personnel.
The contractor shall show (by calculation or otherwise) that no harmful voltages can be present or design additional facilities to prevent excessive voltages. Such facilities may consist of dedicated pipeline earthing and/or the installation of polarization cells or surge arrestors across isolating joints/flanges and across the output terminals of dc voltage sources.
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6.2.11 Lightning protection
In areas of lightning activity the contractor shall install suitable lightning protection to protect the pipeline isolation and cathodic protection equipment. This should consist of suitably rated surge arrestors. Surge arrestors shall be mounted across isolating joints/flanges and across the output terminals of dc voltage sources.
6.2.12 Surge arrestors
Surge arrestors required to prevent elevated voltages due to faults in adjacent electrical power systems or lightning shall be of the spark gap type and shall be such that :
- the impulse breakdown voltage of the electrodes is lower than that of the isolating joint across which they are mounted;
- the spark gap is capable of discharging the expected lightning currents without sustaining damage;
- the spark gaps are fully encapsulated to prevent sparks in open atmosphere and to protect the spark gaps from moisture.
6.3 Installation of Galvanic Anode Systems
Anodes shall be installed according to design specifications and drawings. Before anode is buried, it is important that any waterproof wrapping material be removed. Typical galvanic anode installations shall be of the following types:
6.3.1 Single packaged anode (IPS-M-TP-750: Part 3)
6.3.1.1 Anodes shall be installed at a minimum distance of 1.5 meter from the pipeline and at least 30 centimeters (1 ft) deeper than the pipeline.
6.3.1.2 The native earth shall be thoroughly tamped around the anode, watered, then backfilled to the surface (After making all anode lead connections and insulating them).
6.3.1.3 Anodes shall be placed 2 meters away from any secondary buried structure and so that the secondary structure does not lie between the anode and the primary structure.
6.3.1.4 In distribution systems, where space limitations are extremely critical and where soil resistivities and auguring conditions permit, anodes shall be placed in auger holes alongside the pipe with the hole being deep enough that reasonable spacing between pipe and anode is obtained.
6.3.2 Multiple galvanic anodes
6.3.2.1 In multiple galvanic installation, the anodes shall be placed in straight line configuration for lowest resistance to earth. The line of anodes may be either perpendicular to the pipeline, or may be along a line parallel to the pipe as per IPS-D-TP-711.
6.3.2.2 A Parallel line of magnesium anodes shall be about 5 meters away from the pipeline, with zinc, this distance shall be about 3 meters for optimum performance.
6.3.2.3 Where anodes and backfill are provided separately, anodes shall be centered in the backfill and the backfill shall be compacted before any additional backfill soil is added. The backfill shall be thoroughly wetted before burial is completed.
6.3.2.4 The connection to the pipe shall be made before more than one anode is installed; it will then be possible to observe the current output of successive anodes as they are connected, and installation shall be halted before the average output per anode falls below 150% of the designed value.
6.3.2.5 One 0.01 ohm measuring shunts shall be installed, in each lead wire, current limiting resistors is not permitted.
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6.3.2.6 The anodes thus installed shall be permitted to operate unrestricted for a period of three weeks or more. This will permit adequate polarization and stabilization of current output. After this time, a current output and pipe-to-soil potential survey shall be made. Resistors shall be installed where needed and the current reduced to the designed value. It is particularly important to check the potential at the midpoints between stations (if they are unequal in size, then at the low point). If these potentials should all be found above 0.85, then the installation is complete.
6.3.3 Extruded ribbon anodes
6.3.3.1 Extruded ribbon anodes (of either magnesium or zinc), shall be plowed-in parallel to the pipeline along sections of bare or poorly coated line where continuous local protection is required.
6.3.3.2 Magnesium ribbon anodes shall be installed in accordance with IPS-D-TP-714.
6.3.3.3 Connections between the pipeline and anode core wire shall be made at intervals to complete the protection circuit. The cross connections shall be made at test points at convenient location, to measure current flow periodically and estimate the rate of anode material consumption. Intervals between cross connections shall not exceed 300 meters.
6.3.3.4 Spacing between the ribbon anode and pipeline is not critical. To remain clear of the pipe during plowing-in operations, a spacing of 1.5 meters may be used.
6.3.3.5 The anode strip shall be deep enough to be in continuously moist soil (at least 0.6 meter).
6.3.3.6 Extruded ribbon anodes of magnesium (or zinc) are furnished bare. Using anodes in earth without a special backfill involves risk of anode passivation and inadequate amounts of current. The anodes shall be plowed-in with suitablespecial backfill according to design specification. An adequate allowance for satisfactory dispersion around the anode, is 32 kg of backfill per 30 meter (100 ft) of ribbon anode.
6.3.4 Connection of galvanic anodes to pipeline
6.3.4.1 The anodes shall be connected to pipeline using the combined marker, test point and bondbox. This equipment shall be made according to DWG. No. IPS-D-TP-712 and installed as shown on DWG. No. IPS-D-TP-711 for the following purposes:
- Pipe to anodes groundbed connection;
- Pipe-to-soil potential measurement;
- Installation of a rotary resistor between anodes and pipeline to allow the anode current control;
- Marking the location of anodes.
6.3.4.2 Anode lead wire shall be connected to a loop shaped cable (called header cable), using suitably sized split bolt (line tap) or compression type connectors and a proper branch type (3 way) splicing kit. Splicing compound shall be applied over the tightened zero resistance connection (see 6.4.2).
6.3.4.3 The coated splice shall be insulated by taping with at least one half-lapped layer of rubber tape and one halflapped layer of electrical insulating tape (see IPS-M-TP-750: Part 13), with the joint insulation overlapping the wire insulation a minimum of 50 mm.
6.3.4.4 The current carrying cable composed of two sections in black color. One section will connect the header cable to terminal No. 1 of "Combined Marker, Test Point and Bondbox", the other section connects pipeline to terminal No. 2.
6.3.4.5 A test wire shall be connected between pipeline and terminal No. 3 at "Combined Marker, Test Point and Bondbox".
6.3.4.6 Thermit welding (cad welding process) shall be used to connect the anode lead wire to the pipeline.
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6.3.4.7 The copper wire connection to the steel main is the most critical insofar as insulation is concerned. At this point, all copper at the connection must be coated completely to avoid the possibility of a shielded copper-steel corrosion cell.
6.3.4.8 All connections must be permanently low resistance. Any gradual development of joint resistance can reduce anode output
6.3.4.9 Insulation of underground connections on galvanic anode installations shall be well done to prevent current wastage. The connection shall be waterproofed completely to prevent possible development of resistance within the joint.
6.4.3.10 Care shall be taken so that lead wires and connections are not damaged during backfill operations. Lead wires shall have enough slack to prevent strain. Anodes shall not be carried or lowered into the excavation by the lead wire.
Notes:
1) The chemical backfill in packaged galvanic anodes will take up moisture slowly even if wet down with water after placing in the auger hole and before completing the earth fill. For this reason, the anode will not attain full output immediately. Depending on the amount of moisture in the earth, it may be a matter of days or even weeks before full output is attained.
2) When bare galvanic anodes are placed in auger holes and backfilled with separate chemical backfill, it is the usual practice to install the backfill dry. There will be a time lag before full current output is attained as in the case with packaged anodes. It is possible to mix the chemical backfill with water and pour the slurry into the auger hole to surround the anode. Full output will be attained immediately. There is, however, danger of shrinkage as the excess water leaves the slurry. This shrinkage may operate to cause ultimate reduction in current output. Backfill installed dry, on the other hand, tends to swell upon taking up moisture developing maximum coupling between the anode and the surrounding earth. For this reason, the use of dry backfill is considered the best practice.
7. INSTALLATION OF CP SYSTEMS FOR COMPACT BURIED STRUCTURES
7.1 General
7.1.1 This Clause 7 outlines procedures for the installation of cathodic protection systems for the of external surfaces of compact buried structures, including tank farms, service station tanks, tower footings, steel pilings (in soil), short well casings, compressor and pump stations, refineries, petrochemical plants and associated pipework.
7.1.2 The installation of cathodic protection systems for compact buried structures is basically similar to the installation of buried pipelines, so, many of the requirements outlined in Clause 6 in respect of buried pipelines are applicable to compact buried structures, with the following exceptions:
a) Before any work is carried out on or near an insulated flange, the area shall be checked for hazardous atmospheres.
b) To avoid risk of electric shock and the possibility of sparking, it is advisable that insulating joints be crossbonded before being disassembled. This precaution is essential for hydrocarbon product lines.
c) Galvanic anodes shall preferably be sited on a line normal to the long axis of the tanks at a distance of about 5 m from the outside surface of the tank; if two anodes are used one shall be positioned on each side of the tank.For a well-coated tank the siting of the anodes is not critical, and they may be sited to suit conditions, at a distance of approximately 3-6 m from the tank.
The anodes shall be buried at a depth which places them in permanently moist soil if possible.
The lifting lugs situated at either end of the tank provide convenient points of attachment for
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anode cables. The lugs shall be scraped carefully to expose the bare metal, and the cable end attached by bulldog clamp or by thermit welding; the coating shall then be made good.
For tanks which are already buried, the cable can be connected to the vent pipe.
The cables from the tanks shall preferably be connected to the cables from the anodes via a test box, including a measuring wire from the tank to enable periodic checks of the steel-to-soil potential to be made, as well as current measurements of the anodes.
d) Impressed current groundbeds shall be arranged symmetrically around a tank or group of tanks. Dependent upon the space available, the groundbeds shall be located not less than one tank diameter from the tank periphery to provide optimum current distribution over the tank bottom. If this is not possible, consideration shall be given to distributing a number of anodes or groundbeds evenly around the periphery of the tank or to installing borehole groundbeds. The top anode of a borehole groundbed shall be at a minimum depth of 10 m to facilitate current distribution.
If flammable liquids are being stored in the tanks, the preferred siting of the groundbeds is outside of the bund walls. Where this is not possible, the groundbeds and all connections shall either be totally buried or, if above ground, comply with the requirements of the electrical classification of the hazardous area (see IPS-E-EL-110/1). This shall also apply to any negative drain point connection to the tank. If borehole groundbeds are used, any steel casing shall be finished below ground level to ensure that any spark hazard due to inadvertent contact between the casing and protected steelwork cannot occur.
7.2 Structure Preparation (to be Considered by Structural Constructor)
7.2.1 The tank foundation mound shall as far as possible be constructed so that it will distribute protection current uniformly to the whole of the underside of the tank. This means that the use of rubble, rock fill, etc., shall be avoided and the mound shall consist of fine-grained and well compacted material, to a minimum depth of 150 mm.
7.2.2 Storage tank bottoms are generally constructed by lap welding individual plates and are therefore electrically continuous. Where groups of tanks are to be cathodically protected, provision shall be made for bonding between individual tanks.
7.2.3 If it is desired to confine the protection current to the tanks, isolating joints shall be installed in all pipelines and fittings connected to the tanks including electrical and instrumentation connections.
7.2.4 If flammable liquids are being stored, such joints shall be located outside the tank bund. Earthing electrodes connected to the tank shall be of zinc, or stainless or galvanized steel.
7.3 Installation of Permanent Reference Electrodes (to be Considered by Structural Constructor)
7.3.1 If the installation of the metallic structure is likely to obstruct correct electrode placement, permanent reference electrodes shall be installed immediately prior to construction. For large structures, consideration shall be given to installation of reference electrodes and associated cabling prior to the laying of foundations. Cabling shall be laid with sufficient free play to allow for foundation movement and structural loading.
7.3.2 Reference electrodes shall be installed as close as possible to the buried structure without touching or shielding the surface. The backfill around the electrode shall have a resistivity no greater than that of the soil surrounding the buried structure. Allowance shall be made for foundation settling when locating reference electrodes.
7.3.3 Where reinforced concrete foundations are to be laid, care shall be taken to ensure that all reference and test point cabling and equipment are electrically isolated from metallic reinforcement materials.
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7.3.4 Reference electrodes, associated cabling and connections shall all be checked for damage prior to installation. Correct operation and electrical isolation of the system shall be confirmed prior to final reinstatement of backfill material.
7.3.5 The actual location of permanent reference electrodes and cabling shall be accurately documented on the as-built drawings.
7.4 Installation of Insulating Flanges, Joints and Couplings
7.4.1 All insulating flanges, joints and couplings shall be installed in accordance with the requirements outlined in Clause 12.
7.4.2 The assembly of an insulating flange requires particular care, to ensure that insulation is not lost due to mechanical failure of the components.
Note:
The use of resistance methods to determine the integrity of insulating flanges in the field can produce unreliable results.
7.4.3 Completed flanges shall be coated in accordance with design specifications and/or IPS-E-TP-270.
7.4.4 Insulating joints shall be checked for insulation integrity by measurement of structure-to-soil potential on each side of the joint, with the reference electrode in the same location. Different potential readings indicate adequate insulation. If the potential readings are the same, a cathodic protection current (or changed cathodic protection current) shall be applied to one side of the joint, and the potential remeasured. If the potentials remain the same on both sides, the joint is not adequately insulating.
8. INSTALLATION OF CP SYSTEMS FOR INTERNAL SURFACES
8.1 General
8.1.1 This Clause 8 outlines procedures for the installation of CP systems for internal surfaces of pipes and structures including heat exchangers, hot water systems, clarifiers, ballast and water storage tanks, cooling conduits and reservoirs, that are in contact with natural waters including seawater and waters of near neutral pH.
8.1.2 Full construction detail and installation procedures of the CP system for each specific type of structure will be specified in design specification and drawings.
8.1.3 Many of the requirements outlined in Clause 6 in respect of buried pipelines are applicable to internal surfaces.
8.1.4 The installer shall be thoroughly familiar with the specifications for the works, and shall ensure that all works are completed in accordance with good industrial practice and the relevant specifications. Departures from design specifications shall be approved by the designer and/or Company and permanently recorded for future reference.
8.1.5 Care shall be exercised to ensure that cables and other components are protected from damage during installation. All cable connections need to provide reliable long-term low-resistance electrical contact.
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8.2 Materials and Equipment Acceptance (or Compliance)
8.2.1 See Sub-clause 5.5.
8.2.2 Impressed current anodes shall be provided with individual lead wires to the rectifier for control and measurement of current output from each individual anode.
8.2.3 Because anode cables may be subject to attack from a high chlorine environment found near some anodes, it is important that the cable insulation and sheathing be resistant to such an environment, or otherwise be suitably oversheathed or protected (see IPS-M-TP-750: Part 7).
8.3 Installation of Impressed Current Systems
8.3.1 Impressed current anodes shall be installed in accordance with design specification and drawings.
8.3.2 Impressed current anodes shall not be directly attached to the internal part of the structure. They are required to be insulated from the structure and, in all cases, the electrical connection is to the positive terminal of the dc power source.
8.3.3 Because anodes are often brittle or have thin film electrodeposited coatings, care shall be exercised to ensure that they are not damaged during handling.
8.3.4 Certain anodes are specifically designed for suspension by their cable tails, and may be lowered into position by the cable. Other anodes generally of the direct immersion type, may require to be lowered into position by separate ropes, as their cable tails are designed for electrical purposes only and not for mechanical suspension. The installation drawings shall be checked before commencement of anode installation.
Notes:
1) Anodes which are in close proximity to a coated steel structure shall be provided with an adequate dielectric shield, designed so that the potential at the periphery of the shield does not exceed -1.2 Volts with reference to a copper/copper sulfate electrode.
2) In the case of cantilever anodes, which are generally rod-shaped and project from the structure, obstruction of the active anode surface can be avoided by using an adequate shroud length to prevent build-up of a calcareous deposit on the structure surface.
3) For safety reasons, suspended anodes, other than light anodes of platinized titanium or mixed metal oxides which are specifically designed to be suspended by their cable tails, shall be supported by a suitable rope of polypropylene (see IPS-M-TP-750: Part 10), to prevent the anode cable bearing the anode weight.
8.3.5 Cable supports shall be corrosion resistant and located so that the cable insulation does not become abraded due to cable movement from wind or electrolyte forces. Cable routes shall also avoid areas of likely damage from physical operations on the structure.
8.3.6 Cable joints shall be completely waterproofed using an appropriate cable-jointing compound (see IPS-M-TP-750: Part 11). Waterproofing is particularly important on the positive side of an impressed current system to prevent localized rapid corrosion and subsequent failure of the corrosion protection system (see IPS-D-TP-719).
Note:
Proper cleaning (degreasing and abrading) of the insulation is necessary to ensure that a watertight bond is achieved between the insulation and the cable-jointing compound. where repairs are carried out, a minimum of 50 mm of cable insulation shall be applied to each side
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of the repaired cable joint.
8.3.7 Anode to cable tail encapsulation for immersed anodes is generally fitted at the factory. Prior to installation the encapsulation shall be carefully inspected for any faults or handling damage during transit.
8.3.8 Anodes which project from support pipes or require centering through insulating sleeves may require inspection after installation.
Note:
Of special importance to be inspected during the installation is to ensure that the anode material and size are in accordance with relevant parts of IPS-M-TP-750, where applicable and/or to the approved specifications.
WARNING:
Where underwater diving inspection or maintenance is likely, structures shall have warning notices displayed advising of the danger of electrical gradients near the anodes and the need to switch off the system prior to diving.
CAUTION:
Signs shall be displayed indicating the presence of any immersed cables or anode support ropes which are not physically protected.
8.3.9 Anodes and their support cables on structures located in flowing fluids shall be designed to withstand vibration and impact.
8.3.10 Requirements of this Standard and local authorities shall be observed during the installation of a transformer/-rectifier especially with regard to ac input, cabling, and positioning.
After installation of a unit, it is important that the following be checked:
a) The input and output terminals are correctly identified, and the structure cable is connected to the negative output terminal prior to connection to the electricity supply.
Note:
When electricity is connected, correct polarity and loop resistance shall be verified by energizing the unit, and checking that the structure potential is shifted in the negative direction.
b) The oil level is correct (if the unit is oil-cooled).
c) The fuse ratings are correct.
8.3.11 Safety precautions
Precautions must be taken to:
a) The effects of lightning, both on the protected structure and via the electricity distribution system (personnel protection aspects shall also be included).
b) Electrical gradients resulting from impressed current systems occurring in water around fully and partially submerged anodes and in waterways adjacent to anode installations.
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Note:
Paralysis and respiratory failure may result if a person comes in contact with electric field strengths greater than 3 V/m in water. Should the design result in a possible electric field strength exceeding this value in waters located close to impressed current anodes, warnings should be given and access to such areas prevented by shielding or by other means.
c) Avoid sparks in the presence of flammable substances and explosive gas mixtures that may be present around oil treating vessels.
d) The cable to anode connections in impressed current systems shall never be disconnected, nor shall the anode be removed while the rectifier is in operation.
e) Usual precautions to prevent fire or explosion must be taken before a cathodic protection system can be installed or repaired in a vessel handling water mixed with oil or gas.
f) The rectifier case, external ac disconnect switch box, and any related metallic equipment must be properly grounded using recognized safe grounding practices.
g) Special gaskets capable of withstanding high temperatures shall be used to mount anodes in fired vessels, particularly if the gaskets are located near the fire tubes.
8.4 Installation of Galvanic Anode Systems
8.4.1 Anodes shall be installed according to design specification and drawings.
8.4.2 The common methods of installation of galvanic anodes are as follows:
a) by direct attachment to the internal part of the structure; or
b) by suspension in the electrolyte from the structure using a cable or a rigid metal support; the cable is connected to the structure above electrolyte.
Note:
For safety reasons, suspended anodes shall be supported by a suitable rope of polypropylene (see IPS-M-TP-750: Part 10) to prevent the anode cable bearing the anode weight.
8.4.3 Anodes which are to be installed flush with the structure may be attached to the structure by either of the following methods:
a) Welding of the anode core to the structure.
b) The use of structure studs nuts to attach the anode core.
8.4.4 In all cases, the anode shall be in reliable long-term low-resistance metallic contact with the structure. This may be achieved by the use of fusion joints, bolted connections, or by direct screwing into the structure surface. Ensure that corrosion resistant materials are used and the joints are effectively insulated (wrapped).
8.4.5 Before immersion of the anodes, it is necessary to remove any material wrapped around them. The anodes shall not be painted and, where necessary, shall be protected from accidental paint application.
CAUTION:
The adequate support of anodes is necessary to avoid possible cable failure.
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8.5 Permanently-Installed Reference Electrodes
8.5.1 If permanent reference electrodes are installed for the measurement of the structure-to-electrolyte potential, it is important that they are continually immersed when in use.
8.5.2 Reference electrodes shall be located in accordance with the design requirements. Each reference cell shall be wired to a termination position by a separate and isolated conductor, insulated from the structure and the electrolyte and protected by continuous conduit. The separate conductors can be installed together using multicore cable.
8.5.3 It is essential that reference cell wiring is electrically shielded between the structure exit point and the termination position.
8.5.4 The most convenient method of mounting reference electrodes inside plant is by means of a "screw-in" assembly such that the electrode can easily be withdrawn for inspection and replacement of either the entire unit or the electrode material. The electrodes can be wired to central monitoring and control equipment. A disadvantage lies in the difficulty of checking the accuracy of the electrodes, once installed.
8.5.5 If it is impossible to use ’screw-in’ mountings, reference electrodes can be attached by suitable non-metallic fixings to the protected surface and the insulated connecting leads brought out through the plant wall through a suitable gland.
8.5.6 At least one reference electrode shall be installed for each cathodically protected compartment. The reference electrode shall be installed at the position where corrosion is most likely, e.g. at junctions of ferrous and non-ferrous materials and/or remote from anodes.
Notes:
1) Care must be taken in placing the reference electrode in the treating vessel. For potential measurements the electrode must be as far from the anodes as possible. In the pressure vessels, the electrode is "Lubricated" (introduced into the vessel against existing vessel pressure) through a gate valve installed in the vessel for that purpose.
2) Contamination of the reference electrode with oil or sediments such as iron sulfide must be avoided. A salt bridge may be used to prevent contamination of the reference electrode.
3) Location of the reference cell near an anode may indicate a higher potential than elsewhere in the vessel.
9. INSTALLATION OF CP SYSTEMS FOR MARINE STRUCTURES
9.1 General
9.1.1 This Clause 9 specifies general construction requirements for the installation of cathodic protection systems that will control corrosion of the submerged zones of marine structures and the buried parts of integral offshore/onshore structures.
Full construction details and installation procedures of the CP system for each specific type of marine structure will be specified in design specification and drawings.
9.1.2 Many of the requirements outlined in Clause 6 in respect of buried pipelines are applicable to submarine pipelines.
9.1.3 Cathodic protection systems installed onshore to protect submarine pipelines shall comply with Clause 6 of this Standard.
9.1.4 The contractor shall be thoroughly familiar with the specifications for the works, and shall ensure that all works are completed in accordance with good industrial practice and the relevant specifications. Departures from design specifications shall be approved by design engineer and/or
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company and permanently recorded for future reference.
9.1.5 It is necessary that precautions be taken in combustible atmospheres to prevent sparking due to potential differences between protected and unprotected structures. Any insulated devices shall be cross-bonded before being separated, and the cathodic protection system switched off.
9.1.6 Care shall be exercised to ensure that cable and other components are protected from damage during installation. All cable connections need to provide reliable long-term low-resistance electrical contact.
9.2 For materials and equipment acceptance (or compliance) see 5.5 of general requirements.
9.3 Immersed Structures
9.3.1 Installation of impressed current systems
9.3.1.1 The installation shall be done under the supervision of a corrosion specialist to verify that the installation is made in accordance with design specification and drawings.
9.3.1.2 Impressed current anodes shall be installed in accordance with design specifications and drawings. Special care shall be taken to avoid damage to anodes and their lead wires during installation. Careful supervision of this phase is most essential to proper long-term performance of the cathodic protection system.
9.3.1.3 Impressed current anodes may be installed by one or more of the following methods:
a) Anodes may be lowered in a casing and are allowed to extend below a termination fitting at the bottom. This method provides a mean of anode retrieval or replacement without diver assistance.
b) Anodes may be installed on platform members using offset steel structural supports attached to the platform members. Diver assistance is required for anode replacement.
c) Anodes may be installed on the sea bottom floor remote from the structure. The anodes may be supported by concrete foundations and buoyancy tanks to minimize the possibility of the anodes becoming covered with mud.
9.3.1.4 Because anodes are often brittle or have thin film electrodeposited coatings, care shall be exercised to ensure that they are not damaged during handling. Certain anodes are specifically designed for suspension by their cable tails and may be lowered into position by the cable. Other anodes, generally of the direct immersion type, may need to be lowered into position by separate polypropylene ropes (see IPS-M-TP-750: Part 10), as their cable tails are designed for electrical purposes only and not for mechanical suspension. The installation drawings and the recommendations of manufacturer shall be checked before commencement of anode installation.
9.3.1.5 Cable supports shall be corrosion resistant and located so that the cable insulation does not become abraded due to cable movement from wind or water forces. Cable routes shall also avoid areas of likely damage from physical operations on the structure.
9.3.1.6 Cable joints shall be completely waterproofed using an appropriate cable jointing compound (see IPS-M-TP-750: Part 11). Waterproofing is particularly important on the positive side of an impressed current system to prevent localized rapid corrosion and subsequent failure of the cathodic protection system (see IPS-D-TP-719).
Note:
Proper cleaning (degreasing and abrading) of the insulation is necessary to ensure that a watertight bond is achieved between the insulation and the cable-jointing compound. Where repairs are carried out, the encapsulation shall include a minimum of 50 mm of the cable insulation each side of the repaired cable joint.
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9.3.1.7 Anode to cable tail encapsulation for immersed anodes is generally fitted at the factory. Prior to installation the encapsulation shall be carefully inspected for any handling damage during transit. Anodes which project from support pipes or require centering through insulating sleeves may require diver inspection after installation.
WARNING:
Where underwater diving inspection or maintenance is likely, structures shall have warning notices displayed advising of the danger of electrical gradients near the anodes and the need to switch off the system prior to diving.
CAUTION:
Signs shall be displayed indicating the presence of any immersed cables or anode support ropes which are not physically protected.
9.3.1.8 Of special importance to be inspected during the installation is to ensure that the anode material and size are in accordance with relevant parts of IPS-M-TP-750 where applicable and/or to the approved specifications.
9.3.1.9 Conductor cable connections to the rectifier, from the anode(s) and the structure, must be mechanically secure and electrically conductive. Before energizing the power source, verify that the negative (-) conductor is connected to the structure to be protected, that the positive (+) conductor is connected to the anode(s), and that the system is free of short circuits. After the direct current power source has been energized by authorization of the supervising corrosion specialist, suitable measurements shall be made to verify that these connections are correct in polarity.
9.3.1.10 Connections between the positive header cable and lead wire(s) from the anode(s) shall be mechanically secure and electrically conductive. The connections must be sealed to prevent moisture penetration and assure electrical isolation from the environment. Submerged connections require seals suitable for the water pressures and environment to which they may be subjected.
9.3.1.11 When installing a suspended anode, where separate suspension is required, care should be taken that the lead wire is not in such tension as to damage the anode lead wire or connections.
9.3.1.12 Requirements of this Standard and local authorities shall be observed during the installation of a transformer/ rectifier especially with regard to ac input, cabling and positioning. Rectifier or other power source shall be installed out of the way of operational traffic and remote from areas of extreme heat or likely contamination by mud, dust, water spray, etc. Where two or more rectifiers are installed, they shall be spaced for proper flow of cooling air.
9.3.1.13 Wiring to rectifiers shall comply with any applicable regulatory codes and with the operator’s specifications. An external disconnect switch in the ac wiring to the rectifier shall be provided.
9.3.1.14 Testing of the power source shall be carried out to ensure adequate electrical connection and that no damage has occurred during installation.
The cables and connections shall be carefully inspected to detect insulation defects. Defects shall be properly repaired.
9.3.2 Installation of galvanic anode systems
9.3.2.1 Anodes shall be installed according to design specification and drawings.
9.3.2.2 Various methods for fixation of anodes to the object to be protected may be employed. The method employed shall be based on an evaluation of the design requirements to electrical connection, loading and stresses in the parts to which the anodes are attached.
9.3.2.3 The common methods of installation of galvanic anodes are as follows:
a) By direct attachment to the structure before structure immersion.
b) By direct attachment to the structure after structure immersion.
c) By placing the anode on the sea-bed and connection to the structure by cable, either above or
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under water level.
d) By suspension in the water from the structure via a cable or a rigid metal support, and connection of the cable to the structure above water.
In all cases, the anode shall be in reliable long-term low-resistance metallic contact with the structure. This may be achieved by the use of fusion joints or bolted connections using corrosion resistant materials followed by effective insulation (encapsulation) of the joints.
9.3.2.4 Before anode immersion, it is necessary to remove any wrapping material. The anodes shall not be painted and, where necessary, shall be protected from accidental paint application.
9.3.2.5 It shall be aimed at minimizing the drag forces caused by the sacrificial anode system.
9.3.2.6 Provisions for in-service installation of future additional current capacity shall be made. Such provisions may include spare j-tubes for additional impressed current cables. Other provisions may be "pig-tails" on pipelines and various sorts of brackets, guides, etc.
9.3.2.7 The anodes shall be attached to the structure in such a manner that they remain secure throughout the service life.
9.3.2.8 The anode core shall be welded to the structure either directly (e.g. on offshore structures) or a cadwelded cable between core and structure is used (e.g. for bracelets around pipelines).
9.3.2.9 The distance between anode and structure depends on the condition of the structure. For coated steel the minimum distance is zero, for a bare structure the minimum is 25 cm. The maximum distance is not critical provided the ohmic resistance of the interconnection is small compared with the anode resistance in the medium.
9.3.2.10 Underwater installation of anodes may be performed with mechanical fixing devices or by welding. Where the latter is done welding shall be performed in a dry environment provided by a hyperbaric chamber. Wet welding shall only be allowed on members where cracks and defects will be harmless. Mechanical fixing devices may not give reliable electrical connections for more than 5 years.
9.3.2.11 Where separate suspension is required, care shall be exercised when installing a suspended anode to ensure that the lead wire is not in sufficient tension to damage the anode lead wire, its insulation, or connections.
9.3.2.12 All galvanic anode installations shall be tested to ensure that electrical continuity exists between the anode and the structure.
9.3.3 Electrical connections
9.3.3.1 Electrical connections between anodes and steel structure shall be made by manual welding or thermit welding (see Clause 13).
9.3.3.2 For pipelines and risers, attachment welding shall be placed at least 150 mm off other welds.
9.3.3.3 Doubler plates shall be used for attachment of anode supports to pressurized parts and highly stressed structural members. Anodes shall not be located in areas with high stress concentrations, e.g. anode joints.
9.3.3.4 Doubler and/or gusset plates shall be installed on anode supports at the time of anode installation. If installed as part of the anode fabrication, these plates are subject to serious damage during anode hauling and handling.
9.3.3.5 Suspended galvanic anodes shall be installed after the platform is set on location offshore, and the anodes shall be tested for good electrical contact to the structure after installation.
9.3.3.6 Welding of doubler plates and anode supports directly on to load carrying members and pressurized parts shall be performed with a qualified welding procedure by qualified welders. Theses welds shall be non-destructively examined as required for welding of these components.
9.3.3.7 Attachments of electrical connections by thermit welding shall be made with a qualified procedure proved to give sufficient bonding and negligible Cu-penetration along grain boundaries.
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The size and shape of the mold shall suit the diameter of the pipe and the anode cable size.
9.3.3.8 Qualification of the thermit welding procedure shall be based on visual examination and mechanical testing of three test welds.
9.3.3.9 The test welds shall be sectioned and examined for bonding and possible excessive Cu-penetration using a microscope with magnification of at least 100 x. The Cu-penetration shall normally be less than 0.3 mm for procedures to be used on risers, while maximum 0.8 mm for procedures to be used on pipelines.
9.3.3.10 The hardness in the heat affected zone shall be determined on the macrosections and shall be within the normal limit specified for the pipeline system.
9.3.3.11 Welds made between anode cores and structural members for offshore facilities shall have the approval of the welding engineer. Procedure testing will often be required. Wet welding is not permitted.
9.3.3.12 Other methods used to connect anodes to structures are often used during retrofit exercises when welding is impossible. These are clamping, clamping plus hard-tipped bolting, flash stud welding in mini habitats, stud shooting, etc.
9.3.4 Corrosion control test stations, connection and bonds
9.3.4.1 Test leads to pipelines associated with offshore structures must be mechanically secure, electrically conductive, and shall be readily accessible.
9.3.4.2 Both the pipe and the test lead wires shall be clean, dry, and free of foreign material at points of connection when the connections are made. The completed connection shall be coated to prevent atmospheric corrosion.
9.3.4.3 Conductive connections to other pipelines or across insulating joints shall be installed as per paragraph 9.3.4.1. All bond connections shall be readily accessible for testing.
9.3.4.4 Steel piles shall be electrically connected by means of a continuous copper cable embedded in the concrete deck, and connected to each pile by a welding process equivalent to cadweld or thermoweld. Fender piles shall be electrically connected to main pier structure by a flexible insulated cable.
9.3.4.5 Current continuity between sections of sheet piling shall be provided by joining of adjacent sections by welding a 25 mm diameter reinforcing bar across the joints at the time of installation.
9.3.4.6 Bollards shall be installed in a manner to prevent any electrical contact between them and the steel pier piling through the reinforcing bars in the concrete deck. This will minimize the possibility of temporarily depleting the cathodic protection of the piling when a ship is moored with steel cables.
9.3.5 Installation of insulating joints/flanges and devices
9.3.5.1 All insulating flanges, or other insulating devices, shall be installed in accordance with the recommendations of the Clause 12.
9.3.5.2 The assembly of an insulating flange requires particular care to ensure that insulation is not lost or damaged due to mechanical failure of the components.
Note:
The use of resistance methods to determine the integrity of insulating flanges in the field can produce unreliable results.
9.3.5.3 Completed flanges shall be coated in accordance with design specifications.
9.3.5.4 Insulating joints shall be checked for insulation integrity, e.g. by the measurement of structure to electrolyte potential across the joint, with the reference electrode in the same location.
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Different potential readings usually indicate adequate insulation. If the potential readings are the same, the cathodic protection current (or changed cathodic protection current) shall be applied to one side of the joint, and the potential remeasured. If the potentials remain the same on both sides, the joint is not adequately insulated.
9.4 Submarine Pipelines
9.4.1 Installation of impressed current systems
9.4.1.1 Impressed current anodes shall be installed in accordance with design specification and drawings.
9.4.1.2 The installation shall be done under the supervision of a corrosion specialist to verify that the installation is made in accordance with design specification and drawings.
9.4.1.3 Impressed current anodes submerged in sea water may be installed by one or more of the following methods:
a) Anodes may be lowered in a casing and are allowed to extend below a termination fitting at the bottom. This method provides a mean of anode retrieval or replacement without diver assistance.
b) Anodes may be installed on the sea bottom floor remote from the structure. The anodes may be supported by concrete foundations and buoyancy tanks to minimize the possibility of the anodes becoming covered with mud.
9.4.1.4 The anodes shall not be mounted on sand and mud unless special precautions are taken to prevent them being submerged as a result of tidal action.
9.4.1.5 When installing a suspended anode where separate suspension is required, care shall be exercised to ensure that the lead wire is not in sufficient tension to damage the anode lead wire, its insulation or connections.
9.4.1.6 Rectifiers or other power sources shall be installed so as to minimize possibility of damage, vandalism, or unauthorized entry.
9.4.1.7 Wiring to rectifiers shall comply with local and national electrical codes or requirements of utility supplying power. An external disconnect switch on ac wiring shall be provided.
9.4.1.8 The conductor (negative lead wire) shall be connected to the pipeline as described in 9.4.3. Conductor connections to the rectifier must be mechanically secure and electrically conductive. Before the power source is energized, it must be verified that the negative conductor is connected to the pipeline to be protected and the positive conductor is connected to the anodes and that the system is free of shorts. After the direct current power source has been energized by authorization of the qualified personnel responsible for corrosion control, suitable measurements shall be made to verify that the connections and polarity are correct.
9.4.1.9 Connections between header cable and conductors from anodes shall be mechanically secure and electrically conductive. All connections between anode lead wires and header cable shall be insulated and sealed to prevent moisture penetration and to ensure electrical isolation from the environment.
9.4.1.10 Where the cables cross a beach, they shall be buried in suitable backfilled trenches, with concrete slabs positioned over the cables to prevent movement or damage, or positioned and fixed in such a manner that cannot be moved or damaged by sea action.
9.4.2 Installation of galvanic anode systems
9.4.2.1 Galvanic anode systems shall be installed in accordance with design specification and drawings.
9.4.2.2 It is important that the anodes are mounted in a manner such as to avoid mechanical damage during handling and installation of pipes. Anode bracelets shall be fastened securely on the pipe. The two segments may be welded together with steel strips in order to ensure satisfactory mechanical connection and proper positioning. Each anode shall be electrically connected to the
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pipe by at least two attachments, preferably one from each half bracelet. The reinforcement of concrete weight coating shall not be allowed to be in electrical contact with pipe or anode.
9.4.2.3 Care shall be exercised so as not to reduce the design surface area in contact with the electrolyte. This requirement is especially applicable to bracelet anodes where there may be a possibility of anodes being covered by insulating material or anti-buoyancy material.
9.4.2.4 The contractor shall acknowledge safe receipt of anodes in writing and shall maintain records which shall correlate anode identification with relevant pipe numbers. A copy of these records shall be supplied to the Company.
9.4.2.5 The contractor shall ensure that anodes are kept undamaged during all operations. Any damaged anodes shall be segregated and reported to the Company.
9.4.2.6 Before an anode is immersed, it is important that any waterproof wrapping material be removed.
9.4.2.7 Anodes must not be painted and shall be suitably protected during any painting operations.
9.4.2.8 Electrical connections for anodes are usually incorporated within the mounting arrangement. For bracelet anodes for pipelines, cable connections to the mounting steel framework are provided and these must terminate on the pipe.
9.4.2.9 All galvanic anode installations shall be tested to assure that electrical continuity exists between the anode and the pipeline.
9.4.2.10 Anode bracelets shall be installed as follows:
a) Exposed steel portions of the anode shall be coated. The primer and dry film thickness of coating shall be the same as that used in pipe coating.
b) The anodes shall be placed centrally over the pipes and clamped tightly in place. The segments shall then be welded or bolted together as indicated on the design drawings. Bolting material shall not be high tensile and limited to a hardness of 300 vickers.
c) Remove the coating from the areas where the bonding leads are to be welded to the pipe. The area must be cleaned to bright metal to ensure proper bonding of the weldment.
d) The bonding leads shall be welded to the pipe by the thermit welding or equivalent process (see 6.2.4). Attachment welds shall be made using consumable and procedures qualified under fully representative conditions. The qualification shall consist of one trial weld which shall be sectioned and subject to macro examination and hardness survey.
The sections shall show no cracking or copper penetration and the hardness shall not exceed 260 vickers.
e) Repair visual damage and holidays in the primer coat on the bracelet and repair the coating over the weld and surrounding area of the pipe.
f) Shield the bracelet with light gage sheet metal or other method approved by the Company representative while installing the concrete coating. Cut back the concrete coating mesh so that it will not be within 50 mm of the anode. An ohm meter shall be used to demonstrate to the Company representative that the reinforcement steel is not in contact with the anode.
g) Gaps between the anode bracelets and between the anodes and the concrete coating shall be filled with concrete or mastic infill to produce a smooth surface across the bracelet with only the exterior curved surface of the anode exposed.
9.4.3 Corrosion control test stations, connections and bonds
9.4.3.1 Electrical continuity between the test point and the pipeline shall be proven by means of a continuity tester, indicating zero resistance.
9.4.3.2 The test point shall, where possible, be constructed prior to the application of the pipeline weight coating system and care shall be taken to ensure that all bare metal is insulated (except for the point of contact used for the test point).
9.4.3.3 Care shall be taken to ensure that the reinforcement in the anti-buoyancy weight coating
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