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مدیر وبلاگ : pc7a
نویسندگان
IPS-C-TP-820
This Standard is the property of Iranian Ministry of Petroleum. All rights are reserved to the owner.
Neither whole nor any part of this document may be disclosed to any third party, reproduced, stored in
any retrieval system or transmitted in any form or by any means without the prior written consent of
the Iranian Ministry of Petroleum.
CONSTRUCTION STANDARD
FOR
CATHODIC PROTECTION
ORIGINAL EDITION
DEC. 1997
Dec. 1997 IPS-C-TP-820
1
CONTENTS : PAGE No.
1. SCOPE...........................................................................................................................................2
2. REFERENCES...............................................................................................................................2
3. DEFINITIONS AND TERMINOLOGY.............................................................................................3
4. UNITS.............................................................................................................................................9
5. GENERAL REQUIREMENTS.........................................................................................................9
6. INSTALLATION OF CP SYSTEMS FOR BURIED PIPELINES..................................................15
7. INSTALLATION OF CP SYSTEMS FOR COMPACT BURIED STRUCTURES.........................32
8. INSTALLATION OF CP SYSTEMS FOR INTERNAL SURFACES.............................................34
9. INSTALLATION OF CP SYSTEMS FOR MARINE STRUCTURES............................................38
10. ELECTRICAL MEASUREMENTS AND TESTS.........................................................................45
11. COMMISSIONING OF CATHODIC PROTECTION SYSTEMS.................................................57
12. INSTALLATION OF ELECTRICAL ISOLATION EQUIPMENT.................................................63
13. THERMIT WELDING OF CATHODIC PROTECTION LEADS..................................................67
APPENDICES
APPENDIX A CONTROL OF INTERFERENCE CURRENTS ON FOREIGN STRUCTURES.....................................................................................70
APPENDIX B MEASUREMENT OF SOIL RESISTIVITY.............................................................81
APPENDIX C MEASUREMENT OF ELECTRODE RESISTANCE..............................................87
APPENDIX D CURRENT DRAINAGE SURVEY..........................................................................90
APPENDIX E DETERMINATION IN-SITU OF THE REDOX POTENTIAL OF SOIL..................92
APPENDIX F INSPECTION OF CP INSTALLATIONS...............................................................96
APPENDIX G INSTALLATION IN HAZARDOUS ATMOSPHERES...........................................98
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1. SCOPE
1.1 This Construction Standard covers the minimum requirements for installation, testing and commissioning of cathodic protection systems (impressed current and galvanic) for buried and immersed steel structures such as buried pipelines, distribution networks, in plant facilities, and marine structures which includes installation, start-up, measurements, testing, commissioning and inspection procedures.
1.2 This Construction Standard is related to the IPS-E-TP-820 and IPS-I-TP-820 and shall be used in conjunction with those standards.
1.3 This Construction Standard is generally applicable to buried structures. For specific structural systems (see Note), this Standard shall also be used in conjunction with the Company project specification and drawings for that structures. Any exceptions to the requirements of this Standard shall be stated in writing and submitted for approval to the Company representative.
1.4 The word "Structure(s)" hereafter in this Standard refers to steel structure(s) to be protected as mentioned above.
Note:
Installations that require special attention, techniques, and materials are not covered. Each such installation requires special considerations based on many influencing factors and cannot be covered adequately in a single standard.
2. REFERENCES
Throughout this Standard the following dated and undated standards/codes are referred to. These referenced documents shall, to the extent specified herein, form a part of this standard. For dated references, the edition cited applies. The applicability of changes in dated references that occur after the cited date shall be mutually agreed upon by the Company and the Vendor. For undated references, the latest edition of the referenced documents (including any supplements and amendments) applies.
BSI (BRITISH STANDARDS INSTITUTION)
BS 1377 "Methods of Tests for Soil for Civil Engineering Purposes"
Part 3: Chemical and Electrochemical Tests
Part 9: In-Situ Tests
BS CP 1003 "Electrical Apparatus and Associated Equipment for Use in Explosive Atmospheres of Gas or Vapor other than Mining Application"
BS 4683 "The Construction and Testing of Flame Proof Enclosures of
(Part 2) Electrical Apparatus"
BS 5501 "Electrical Apparatus for Potentially Explosive Atmospheres"
BS 5750 (ISO 9002) "Quality Systems"
Part 2: Specification for Production and Installation
BS 6651 "The Protection of Structures against Lightning"
BS 7361 "Cathodic Protection"
Part 1: Code of Practice for land and Marine Applications
BS 7430 "Earthing"
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ASTM (AMERICAN SOCIETY FOR TESTING AND MATERIALS)
G 51 "Test for pH of Soil"
IPS (IRANIAN PETROLEUM STANDARDS)
IPS-E-TP-820 "Engineering Standard for Electrochemical (Cathodic and Anodic) Protection"
IPS-I-TP-820 "Inspection Standard for Monitoring Cathodic Protection Systems"
IPS-E-TP-100 "Engineering Standard for Paints"
IPS-C-TP-274 "Construction Standard for Coatings"
IPS-E-TP-270 "Engineering Standard for Coatings"
IPS-M-TP-750 "Materials and Equipment Standard for Cathodic Protection"
IPS-C-TP-102 "Construction Standard for Paintings"
IPS-E-TP-270 "Engineering, Construction and Material Standard for Fencing"
IPS-M-EL-150 "Transformer Rectifiers for Cathodic Protection"
IPS-E-EL-100/1 "Earthing, Bonding and Lightning Protection"
3. DEFINITIONS AND TERMINOLOGY
For the purposes of this Standard the following definitions shall apply:
Attenuation
The progressive decrease in potential and current density along buried or immersed pipeline in relation to distance from the point of injection.
Bonds:
Bond
A piece of metal conductor, either solid or flexible, usually of copper, connecting two points on the same or on different structures, to prevent any appreciable change in the potential of the one point with respect to the other.
Continuity bond
A bond designed and installed specifically to ensure the electrical continuity of a structure.
Note:
This may be permanent or temporary. In the latter case it is used to connect two sections of a structure which would otherwise be disconnected during a modification or repair.
Drainage bond
A bond to effect electric drainage.
Remedial bond
A bond installed between a primary and a secondary structure in order to eliminate or reduce corrosion interaction.
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Resistance bond
A bond either incorporating resistors or of adequate resistance in itself to limit the flow of current.
Safety bond
A bond connecting the metallic framework or enclosure of electrical apparatus with earth, in order to limit its rise in potential above earth in the event of a fault, and so reduce the risk of electric shock to anyone touching the framework or enclosure.
Bond resistance
The ohmic resistance of a bond including the contact resistance at the points of attachment of its extremities.
Cathodic protection
The process to reduce or prevent corrosion of metal structures in contact with an electrolyte by the flow of direct current from the electrolyte into the structure surface.
Cathodic protection station
A combination of equipment installed to provide cathodic protection to the structure(s).
Company-approved drawings
Company-approved drawings consist of appropriate standard drawings for cathodic protection (IPS-D-TP standards) and drawings prepared by the designer of the cathodic protection system to show the location and details for the construction of the CP system and appurtenances.
Current density
The amount of current per unit area of the steel surface coated or uncoated, in contact with the electrolyte.
Deep groundbed
One or more anodes installed vertically at a depth of 100 ft (30 m) or more below the earth’s surface in a drilled hole for the purpose of supplying cathodic protection to the external surface of a metallic structure in contact with a common electrolyte.
Open hole (Deep groundbed)
An installation in which the anodes are surrounded only by an aqueous electrolyte.
Closed hole (Deep groundbed)
An installation in which the anodes have been surrounded by backfill.
Drain point
The point on the pipeline/structure where the connection of the negative terminal of the cathodic protection voltage source is made to conduct (drain) the returning current from the pipeline/structure to the voltage source.
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Driving potential (of a sacrificial anode system)
The difference between the structure/electrolyte potential and the anode/electrolyte potential.
Electrolyte
A conductive liquid or material such as soil or water in which an electric current can flow.
Foreign structures
Metal structures, other than the structure under consideration, in contact with the same electrolyte as the structure, and which are or may become under the influence of the structure’s cathodic protection system.
Foreign structures may be owned by the Company or other organizations and may or may not be equipped with cathodic protection.
Groundbed
The system of buried or submerged electrodes, to conduct the required current into and through the electrolyte to the steel surface to be protected.
Impressed current
The current supplied by a transformer/rectifier or other direct-current source (specifically excluding a sacrificial anode) to a protected structure in order to attain the necessary protection potential.
Instantaneous-off potential
The structure/electrolyte potential measured immediately after the synchronous interruption of all sources of applied cathodic protection current.
Joints:
Isolating joint
A joint or coupling between two lengths of pipe, inserted in order to provide electrical discontinuity between them.
Insulated flange
A flanged joint between adjacent lengths of pipe in which the nuts and bolts are electrically insulated from one or both of the flanges and the jointing gasket is non-conducting, so that there is an electrical discontinuity in the pipeline at the point.
Interaction test
A test to determine the severity of corrosion interaction between two buried or immersed structures.
Interference current
In its broadest sense, a direct current flowing through paths other than the intended circuit. In this Construction Standard, interference current is current discharged to the electrolyte from a structure that may be either (1) not an intended part of the circuit or (2) if intended, then not adequately
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connected to the current source.
Midpoint
The point on a pipeline between two cathodic protection stations where the influence of the two cathodic protection stations is expected to be equal and the protection levels are usually lowest.
Natural potential
The pipe to soil potential measured when no cathodic protection is applied and polarization caused by cathodic protection is absent.
"Off" potential
The pipe to soil potential measured immediately after the cathodic protection system is switched off and the applied electrical current stops flowing to the pipeline surface, but before polarization of the pipeline has decreased.
"On" potential
The pipe to soil potential measured while the cathodic protection system is continuously operating.
Pipeline
The pipeline or pipelines with associated equipment as defined in the scope of the cathodic protection design contract.
Polarized potential
Pipe-to-soil potential free of errors caused by currents flowing from the applied cathodic protection system. The reading is normally measured within 100 milliseconds and 3 seconds of simultaneously switching off all cathodic protection current sources that may influence the measurement.
Polarization
The change of the pipe to soil potential caused by the flow of dc current between an electrolyte and a steel surface.
Potential gradient
Difference in potential between two points in the soil caused by current flowing off the pipeline and through the soil.
Specification
Detailed procedures and requirements for the installation of the CP systems and appurtenances prepared by the Company designer. Installation specification may incorporate this Standard by reference, but should also include specification of the alternate provisions of the standard and requirements for matters not covered by the standard.
Redox potential
The equilibrium electrode potential for a reversible oxidation-reduction reaction used for assessing anaerobic microbial activity.
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Remote earth
An electrode location far enough from the pipeline/structure that further separation results in no significant change in the circuit parameters.
Reference electrodes:
Reference electrode
An electrode the potential of which is accurately reproducible and which serves as a basis of comparison in the measurement of other electrode potentials.
Note:
Sometimes termed a "half cell".
Calomel reference electrode
A reference electrode consisting of mercury and mercury chloride (calomel) in a standard solution of potassium chloride.
Copper/copper sulphate reference electrode
A reference electrode consisting of copper in a saturated copper sulphate solution.
Silver/silver chloride reference electrode
A reference electrode consisting of silver, coated with silver chloride, in an electrolyte containing chloride ions.
Standard hydrogen electrode
A reference electrode consisting of an electro-positive metal, such as platinum, in an electrolyte containing hydrogen ions at unit activity and saturated with hydrogen gas at 1 atm.
Sensing electrode
A permanently-installed reference electrode used to measure the structure electrolyte potential and to provide a reference signal to control the protection current of an automatic impressed current system.
Resistivity
The electrical resistance of a unit volume of a material; the reciprocal of conductivity. Resistivity is used in preference to conductivity as an expression of the electrical character of soils (and waters) since it is expressed in whole numbers.
Resistivity measurements indicate the relative ability of a medium to carry electrical currents. When a metallic structure is immersed in a conductive medium, the ability of the medium to carry current will influence the magnitude of galvanic currents and cathodic protection currents. The degree of electrode polarization will also affect the size of such currents.
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Stray currents
Electrical currents running through the electrolyte, originating from a foreign dc source, causing interaction with the corrosion and cathodic protection processes of the pipeline. Stray currents may also originate from the pipeline’s cathodic protection system and act upon foreign structures/pipelines.
Structures:
Protected structure
Any metallic part to which cathodic protection is applied.
Unprotected structure
A structure to which cathodic protection is not applied.
Primary structure
A buried or immersed structure cathodically protected by a system that may constitute a source of corrosion interaction with another (secondary) structure.
Secondary structure
A buried or immersed structure that may be subject to corrosion interaction arising from the cathodic protection of another (the primary) structure.
Structure/electrolyte potential
The difference in potential between a structure and a specified reference electrode in contact with the electrolyte at a point sufficiently close to (but without actually touching) the structure to avoid error due to the voltage drop associated with any current flowing in the electrolyte.
Note:
Similar terms such as metal electrolyte potential, pipe electrolyte potential, pipe soil (water) potentials etc., as applicable in the particular context are also used.
Structure-to-structure voltage
(Also structure-to-structure potential). The difference in voltage between metallic structures in a common electrolyte.
Sulphate-reducing bacteria
A group of bacteria found in most soils and natural waters, but active only in conditions of near neutrality and freedom from oxygen, which reduce sulphates in their environment with the production of sulphides.
Supplementary specifications
Supplementary specifications prepared by the Company to define which of the alternate materials and procedures provided in the standard and to provide for conditions, materials, and procedures not covered by this Standard.
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Synchronized timer
A cyclic timer that can be synchronized to operate simultaneously with one or more other timers.
Abbreviations
Ag/AgCl Silver/Silver Chloride as used for the Silver/Silver Chloride type of reference electrode.
Cu/CuSO4 Copper/Copper Sulphate as used for the Copper/Copper Sulphate type of reference electrode.
ac Alternating Current.
dc Direct Current.
CP Cathodic Protection.
T/R Transformer Rectifier.
4. UNITS
This Standard is based on International system of units (SI), except where otherwise specified.
5. GENERAL REQUIREMENTS
5.1 Construction Works
5.1.1 All construction works performed on cathodic protection systems shall be executed in strict accordance with the Company approved construction drawings and specifications.
5.1.2 All construction works performed on cathodic protection systems shall be under the supervision of a company inspector(s). It shall be the inspector’s function to verify that the installation is made in strict accordance with the drawings and specifications (see 5.1.1). Any exceptions are made only with the express consent of qualified personnel where it can be demonstrated that the effectiveness of the system is not impaired. It shall also be the inspector’s function to verify that construction methods and techniques are in accordance with good practices.
5.1.3 All works shall be executed in a workmanlike manner and shall present a neat, quality appearance when completed. All workmanship shall meet with the Company’s approval. The contractor shall re-execute, at his own expense, all inferior workmanship which does not meet the approval of the Company.
5.2 Contractors Responsibilities
5.2.1 The work to be accomplished by the contractor includes furnishing qualified labor, materials, appliances, equipment, transportation, installation, supervision, and any services required to construct and complete cathodic protection system in accordance with the drawings and specifications that describe the installation.
5.2.2 The contractor works and duties normally include, but are not limited to, the following:
5.2.2.1 Supply of all construction materials which are not provided by Company.
5.2.2.2 Transport of the materials and equipment from the delivery locations up to the site and on site.
5.2.2.3 Installation, connection and checking of the cathodic protection systems including but not limited to:
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a) Concrete plinth for cathodic protection station equipment.
b) Installation of T/rectifier(s).
c) Trenching, laying and backfilling of ac and dc cables.
d) Drilling, installation, connection and backfilling of anodes, deepwell(s) with concrete bases, if any.
e) Installation, connection, and backfilling of anodes, horizontal and/or vertical groundbed(s), if any.
f) Installation of ac supply box(es).
g) Installation and connection of positive and negative test boxes.
h) Connection of ac supply cables to fuse-disconnecting switch.
i) Installation, connection and backfilling of galvanic anodes, if any.
j) Installation and connection of current test box(es) for galvanic anodes, if any.
5.2.2.4 Reinstatement of the lands and surrounding area at CP equipment locations.
5.2.2.5 Cables connections to structure and reconditioning of structure coating at CP equipment locations.
5.2.2.6 Installation and connection of earthing circuit at CP station(s).
5.2.2.7 All the sundry works to complete the installation for the CP system(s).
5.2.2.8 Installation and connection of test boxes (bond boxes) at insulating joints/flanges, pipe crossing, etc.
5.2.2.9 Installation and connection of potential test points distributed on the structure.
5.2.3 The contractor shall set up and maintain such quality and inspection systems as are necessary to ensure that the goods and services supplied comply in all respects with the requirements of this Construction Standard. The Company shall assess such systems against the recommendations of the applicable parts of ISO 9002 or BS 5750 Part 2 and shall have the right to undertake such surveys as are necessary to ensure that the quality assurance and inspection systems are satisfactory.
5.2.4 The Contractor’s personnel-in-charge of cathodic protection shall be fully qualified for this work. The contractor, before starting cathodic protection work shall submit qualifications of all his technical employees-in-charge of cathodic protection to the engineer for his approval. If any employee shows lack of knowledge in the function for which he is responsible, the engineer will require his immediate replacement and the contractor shall comply with the engineer’s instructions without stopping the progress of the cathodic protection work.
5.2.5 The contractor shall ensure that the final installation of the CP system conforms to the Company-approved drawings and specification.
5.2.6 The contractor shall provide access to the work at all times for inspection by the Company.
5.2.7 The contractor shall bring to the attention of the Company project manager any areas of the drawings and specifications that conflict or do not meet safe and acceptable installation practices. The conflicts and exceptions shall be brought to the Company’s attention and approval prior to installing any equipment involved and early enough to avoid adverse effects on the construction schedule. Deviations from design specifications shall be permanently recorded for future reference.
5.2.8 The contractor shall be responsible for keeping his work areas clean and free from debris and waste material at all times. The interior of all test boxes, T/R cabinets, etc., shall be cleaned of dust, dirt and loose materials.
5.2.9 The contractor shall check and energize the CP system(s).
5.2.10 After the complete installation of the cathodic protection systems, the contractor has to:
- Make a structure-to-soil potential survey before energizing.
- Adjust the CP station(s) to meet the potential level required.
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- Make a structure-to-soil potentials survey at each test point along the structure.
- Check the insulation at pipe-casings (if any), insulating flanges/joints and all insulation at services.
- Make the influence measurements and take the necessary action to compensate the influence (if any).
5.3 Scheduling of Installation
The installation of permanent cathodic protection system needs to be co-ordinated with the piping, insulation, electrical, and instrument disciplines to ensure a proper completion. The installation of the cathodic protection system should begin only after the majority of mechanical construction is complete.
5.4 Materials Receiving, Storage and Handling
5.4.1 All materials provided by the Company and/or contractor shall be new and meet the requirements of relevant IPS standards such as IPS-M-TP-750. All materials provided by contractor shall also meet the Company’s approval.
5.4.2 The contractor shall take delivery of the items shown on the drawings, listed on the bill of materials and/or specified within the contract documents as company supplied materials. The contractor becomes responsible for company supplied materials, upon receipt by the contractor.
5.4.3 The contractor shall notify the Company of any discrepancies between the "actual materials received" and list of "Company Furnished Materials" within seven days of receipt of the materials, otherwise the contractor will be held responsible for having received all materials as listed.
5.4.4 All materials necessary for a complete operable installation not designated company supplied, shall be supplied and installed by the contractor. Any materials required or called for on the drawings and not listed in bill of materials shall be provided by the contractor. Verification of quantities listed on the bill of materials is expected at early stages of work.
All tools, measuring instruments and installation equipment for use by contractor shall be provided by himself.
5.4.5 It shall be the responsibility of the contractor to determine what materials he must expedite to maintain the agreed construction schedules.
5.4.6 It shall be the responsibility of the contractor to provide on site storage for all the equipment and materials to keep them clean, dry and free from possible hazards in the field prior to installation. Materials shall not be released to the field until they are needed for construction so as to minimize inadvertent damage.
All materials shall be stored above the ground so as to be kept free of dirt, grease, paint spray or other foreign matter and shall be protected from corrosive environments and/or marine environmental.
5.4.7 Materials shall be stored in such a way as to enable Company representative to carry out quick stock checks at any time.
5.4.8 A material control system shall be maintained by contractor which will facilitate determining the balance and location of materials at all times.
5.4.9 All materials damaged or lost in handling, processing or storage must be repaired and/or replaced by contractor at his own expense.
5.4.10 The contractor shall be responsible for the safety, security, and condition of all equipment and materials from the time of delivery until commissioning is complete.
5.4.11 The contractor shall provide handling facilities for all equipment and installation materials during the construction period.
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Notes:
1) Care shall be exercised in transportation and handling of transformer/rectifiers.
- Oil-cooled transformer/rectifiers shall be protected against the ingress of foreign material (storage by contractor).
- Air-cooled transformer/rectifiers can be stored in dry, protected areas without special treatment.
2) Special care shall be taken to avoid cracking or damaging anodes, wire and wire connection to anode during handling and installation.
Careful supervision of this phase is most essential to proper long-term performance of the cathodic protection system.
3) If graphite or high silicon cast iron anodes are used for groundbed construction, they shall be transported and handled with care because they are relatively brittle. The insulated leads furnished with the anodes by the manufacturer should be protected from damage to both the wire insulation and the connection between wire and anode. Although these connections are well made, it is not the best practice to support the full anode weight by the lead wire alone; although the connection may not fail mechanically, the strain may be sufficient to damage insulating material at the connection enough to permit current leakage that would cause corrosion failure of the connection.
5.5 Materials and Equipment Acceptance (or Compliance)
5.5.1 General
The contractor shall inspect all materials and equipment upon receipt. Any damaged or missing items shall be reported by the contractor to the Company representative. Because of the inaccessible nature of much of the cathodic protection equipment in service, it is necessary to confirm, prior to shipment to site and prior to installation, that materials and equipment comply with the appropriate standard specification (see IPS-M-TP-750). Clauses 5.5.2 to 5.5.6 inclusive indicate the types of checks and tests which shall be undertaken by contractor to avoid unnecessary and protracted delays while replacements are sought or repairs are undertaken.
5.5.2 Galvanic anodes
5.5.2.1 Anodes should be inspected for the following:
a) Freedom from electrical damage.
b) Electrical security and continuity of connections.
c) Anode to core continuity.
d) Correct metal mass.
e) Correct profile.
f) Compliance of anodes (including anode backfill) with IPS-M-TP-750.
5.5.2.2 Insulation of all cable tails shall be inspected for presence of nicks, cuts or other forms of damage.
5.5.2.3 Packaged anodes shall be inspected and steps taken to assure that backfill material completely surrounds the anode. The individual container for the backfill material and anode should be intact. If individually packaged anodes are supplied in waterproof containers, that container must be removed before installation. Packaged anodes should be kept dry during storage.
5.5.2.4 Electrical continuity between anode and lead wire shall be tested without compromising the integrity of the package.
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5.5.2.5 Other galvanic anodes, such as unpackaged "Bracelet" type or ribbon, should be inspected for assurance that dimensions conform to design specifications and that any damage during handling does not affect application. If a coating is used on bands and the inner side of "Bracelet" anode segments, it should be inspected and, if damaged, repaired before the anodes are installed.
5.5.2.6 When a separate suspension such as rope is used to support the weight of an anode, the suspension system should be inspected for damage and all defects repaired.
5.5.2.7 In the case of weld-on type galvanic anodes, the steel cores shall be inspected for conformance to specifications. If the anode cores have welded joints or connections, these shall be inspected to assure compliance with structure welding specifications.
5.5.2.8 When galvanic anode suspension cables are used for the lead wire, the cables shall be inspected for strength and good electrical contact with the anode. Where separate suspension cables are used, care shall be taken to insure that anode lead wires are not in such tension to damage the lead wires or connections.
5.5.2.9 If coatings are specified for galvanic anode supports or suspension cables, they shall be visually inspected and the coatings repaired if damaged.
5.5.3 Impressed current anodes
5.5.3.1 Impressed current anodes shall be inspected for conformance to standard specifications (see IPS-M-TP-750) concerning correct anode material and size, length of lead wire, and secure cap, if used. Care shall be exercised to avoid cracking or damaging anodes during handling and installation.
5.5.3.2 Lead wire shall be carefully inspected to detect defects in insulation. Care shall be taken to avoid damage to insulation on wire. Defects in the lead wire must be repaired or the anode must be rejected.
5.5.3.3 Anode backfill material shall conform to standard specifications (see IPS-M-TP-750).
5.5.4 Cables
5.5.4.1 Cables shall be inspected to ensure that cable runs can be achieved, preferably in one take-off from a reel or drum and that the cable is of correct construction for the intended application.
5.5.4.2 Insulation of all cables should be inspected for presence of nicks, cuts, cracks, abrasions, excessive thinning below specified thickness or other forms of damage.
5.5.5 Transformer/rectifier equipment
Testing should be carried out prior to acceptance of a transformer/rectifier unit, to confirm compliance with the standard specification (see IPS-M-EL-155) and to ensure that the equipment is suitable for the intended purpose.
The following tests shall be carried out on transformer/rectifier equipment:
a) Visual inspection to ensure that all rectifier and surge protection equipment and all specified current outputs, have been provided.
b) Polarity check to ensure that output terminals are correctly identified.
c) A step-by-step check of the unit output against calculated load, to ensure that a uniform control pattern is available.
d) Insulation resistance tests shall be conducted and recorded on all transformer/rectifier(s) in accordance with company-approved testing method to ensure that the equipment has neither deteriorated nor been damaged during shipment.
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e) The contractor shall ensure that oil-cooled transformer/rectifier(s) are filled to the normal liquid level before being placed in operation. Five samples of insulation oil should be tested for dielectric strength and have the results and the average recorded if required by the Company.
f) Functional tests of time switches to be installed.
g) Functional tests of other special equipment to be fitted.
5.5.6 Prefabricated insulating joints
Where appropriate, each insulating joint shall be electrically tested, pressure tested, and finally electrically re-tested. Where supplied for welding into position, the associated pipe pieces shall be of sufficient length to prevent damage to the joint insulation by heat transfer during the welding process. During welding the manufacturer’s recommendations on cooling rate shall be followed.
5.6 Drawings
5.6.1 Location of equipment
The location drawing(s) indicate the extent and general arrangement of the cathodic protection systems. Exact locations, distances and levels will be governed by actual field conditions. The contractor shall verify all dimensions in the field for company approval prior to installation.
5.6.2 Other systems
The contractor shall be responsible to examine the architectural, mechanical and structural drawings to determine if any interferences or discrepancies arise. Any interferences or discrepancies found shall be reported to the Company as soon as practicable.
5.6.3 Changes
If any departures from the original intent of the drawings and/or specifications are deemed necessary by the contractor, details of such departures with drawings, if necessary, together with reasons for the departure shall be submitted to the Company as soon as practicable for approval. No such departure shall be made without the prior written consent of the Company.
5.6.4 As-built
5.6.4.1 A set of as-built construction drawings shall be marked up, by the contractor in red on a daily basis. The Company shall have access to view this set of drawings at all times.
5.6.4.2 Before final acceptance of the work, the contractor shall furnish the Company with one completely detailed set of "as built" drawings showing final locations and connections for all work carried out by the contractor. Such as-built drawings will include all pertinent notes and dimensions necessary to show clearly the location of all equipment and connections.
5.6.4.3 As-built drawings will be verified and shall not be deemed complete until they are to the satisfaction of the Company.
5.7 Excavation and Backfilling
5.7.1 The contractor shall provide all necessary excavating, shoring, sheathing, bracing, pumping and backfilling required to install groundbeds, cables and connections as specified. when excavation is carried below grade, the fill to grade material shall be well tamped in such a manner
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as to meet the approval of the Company. In no case shall any frozen earth be used for backfilling, nor shall any backfilling be placed on or against frozen earth. Trenches under roads and paved areas shall be backfilled with coarse sand to the approval of the Company. Excavated material shall not be used.
5.7.2 Any earth excavating procedure presents safety hazards related to the presence of unstable soils, water, released products, and moving equipment. Personnel involved in excavation, equipment installation, and bacfilling shall be knowledgeable about and shall follow the safety standards.
5.7.3 The excavation shall provide adequate space for the installation of anodes, cables, and ancillary equipment.
5.7.4 Special attention shall be given to sloping or shoring the sides of the excavation to make them stable.
5.7.5 Metallic pipelines shall be located through use of a line locator and mechanical probe. Excavations within 600 mm of pipe shall be done by hand.
Non-metallic lines in the immediate proximity of excavations shall be exposed by hand.
5.7.6 Damage to pipelines, coatings, conduit, cable or other buried equipment as a result of excavation shall be repaired in accordance with IPS-C-TP-274 at cost to the contractor prior to backfilling.
5.8 Painting
The contractor shall touch-up all electrical and control equipment marred by shipment or erection, using the same color and type of finish as the original-according to Company standard for painting (see IPS-C-TP-102). The transformer/- rectifier cabinet must not be coated with mastics, tars, or any other like materials.
5.9 Return of Unused Materials and Equipment to Company
At the end of the work contractor shall provide a list of unused materials and equipment for company representative for return of them to Company store allocated for the purpose.
6. INSTALLATION OF CP SYSTEMS FOR BURIED PIPELINES
6.1 General
This Clause 6 specifies minimum requirements for the installation of cathodic protection systems that will control corrosion of the buried pipelines.
6.2 Installation of Impressed Current Systems
6.2.1 Groundbeds
6.2.1.1 Because anodes are often brittle, care shall be exercised to ensure that they are not damaged by handling. Unless especially designed, they shall not be suspended or lowered by their cable tails because connections are essentially electrical and not mechanical.
6.2.1.2 Proper implements, tools, and facilities shall be provided and used for the safe and convenient performance of the work.
6.2.1.3 All materials shall be examined carefully for damage and other defects immediately before installation. Defective materials shall be marked and held for inspection by the Company, who may prescribe corrective repairs or reject the materials.
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6.2.1.4 Anodes shall be installed in the center of any backfill and the backfill shall be gently tamped into place around the anode. Care shall be taken to prevent anode breakage.
6.2.1.5 On completion of the installation of a groundbed, the resistance of the groundbed to remote earth should preferably be measured by using an alternating current earth tester. Measured resistance should be compared with the design resistance.
6.2.1.6 Resistance in a groundbed may be lowered by permanent adding water to each anode by using plastics water piping and drip-irrigation fittings. However, where groundbed resistance is still too high, the groundbed will need to be extended.
6.2.1.7 The groundbeds shall be of the following forms as will be specified by the design documents.
6.2.1.7.1 Horizontal groundbed
Horizontal groundbeds shall be constructed in locations as determined in the design drawings and with the following considerations:
a) Anodes shall be installed horizontally in a group and connected in parallel in the trench at a minimum depth of 2000 mm and at 4500 mm centers, unless otherwise specified by the design documents (see standard drawing No. IPS-D-TP-706).
b) A bedding of the trench shall be made 600 mm wide and with depth and length as specified on the design drawings. The trench walls shall be vertical throughout and the bedding shall be tamped to provide a uniform surface.
c) Anodes shall be installed with a minimum of 150 mm compacted metallurgical grade coke breeze encapsulating the circumference and a minimum of 2250 mm coke breeze extending beyond each end. The anodes lead wires shall then be brought out of the coke breeze and spliced, taped, and coated to the positive header cable (see 6.2.4.2).
d) The coke breeze shall be thoroughly and properly tamped; for maximum coupling between anode and earth. Care shall be exercised during backfilling to avoid damage to the anode. Loose backfill can give disappointingly high resistances and shorten anode life.
e) The process of tamping down shall be achieved in stages after every 10 cm layer of coke breeze has been poured into the trench. The tamping down process while having to be very thorough shall in no way damage the anodes.
The groundbed excavation shall then be backfilled with fine soil by hand until a minimum cover of 200 mm over coke breeze is achieved. Power equipment shall then be used to restore the excavation to original ground level.
Before backfilling the trench, the vent pipes shall be placed at their predetermined locations on each anode and filled with gravel.
If the backfilling operation does not produce sufficient compaction to eliminate the possibility of future settling, a berm shall be installed over the backfill such that original elevations will be met.
f) The header cable shall then be laid on 100 mm layer of fine sand covered with a further 100 mm of sand. The remaining space of the trench shall be backfilled with earth to ground level. For the protection of the cable, protective tiles or bricks shall then be installed on top of the sand as shown on the standard drawing. The remaining space of the cable trench shall be filled with backfill.
Notes:
1) In horizontal installations, ditch width at anode depth shall be that of the design width of the carbonaceous backfill layer. Where this is not possible because of trenching conditions, form boards may be used to restrict the backfill. After the carbonaceous material and anodes have been placed inside the form boards and tamped earth outside, the form boards must be withdrawn. The coke breeze shall be retamped to fill the space occupied by the form boards.
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2) Top soil shall be stripped and stockpiled at the commencement of excavating and redistributed over the excavated area upon completion.
3) Maximum anode loading shall be determined by employing good engineering practices.
4) The contractor shall give due consideration to the use of anode irrigation equipment. Where applicable, complete details of proposed equipment and installation methods shall be provided for approval of the Company.
5) The groundbed shall be located at the distance from any buried metal structure as specified by the design documents with reference to IPS-E-TP-820. When possible the distance shall not be less than 100 mm.
6.2.1.7.2 Vertical groundbed
Vertical groundbeds shall be constructed in locations as determined in design drawings and with the following considerations:
a) Anodes shall be installed vertically in a group (at straight line) in separate holes and connected in parallel as shown in the standard drawing No. IPS-D-TP-705.
b) The anode hole shall be at least 1300 mm (4 ft) deeper than the length of the anode rod and 200 mm (8 in) more in diameter than the diameter of the anode.
c) The bottom of the hole shall be filled to a depth of 300 mm (1 ft) of metallurgical grade coke breeze, and tamped until well packed. Tamping will reduce the anode-to-soil resistance, thereby increasing the efficiency of the installation. The anode must be centered carefully in hole, and the backfill material shall be poured into the hole to cover the anode. The backfill shall be gently tamped into place around the anode. When tamping with power tampers (preferred) or by hand, particular care must be exercised to prevent damage to the anode or anode lead wire.
d) This procedure is repeated until the anode is covered by at least 300 mm (1 ft) of backfill. After making the electrical connection of anode lead wire to header cable the vent pipe shall be placed in its predetermined location and filled with gravel.
Note:
The purpose of the gravel is to provide a gas vent for the oxygen, chlorine and, in some special cases, hydrogen, which may evolve under various conditions from the anode area.
e) The hole shall then be backfilled with the excavated earth to ground level. The header cable shall be laid on 100 mm layer of fine sand covered with a further 100 mm of sand. For the protection of the cable, protective tiles or bricks shall be installed on top of the sand as shown on the standard drawing. The remaining space of the cable trench shall be filled with backfill.
Note:
(See Notes 2, 3, 4 and 5 of paragraph 6.2.1.7.1).
6.2.1.7.3 Deep-well groundbed
6.2.1.7.3.1 General
Deep-well groundbeds shall be constructed in locations as determined in the design drawings, and with the following considerations:
a) The anode bed for a deep-well groundbed shall be drilled with a rotary rig (using mud or air) or by cable tools where applicable.
b) Depending on the type of drilling rig used, it may be possible to use the rig itself for placing
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the anode system in the hole where a well is being drilled in soft formations which cannot be depended on to hold an open hole without collapsing, a rotary rig can continue circulating drilling mud in the hole, after reaching design depth, until just prior to placing the anode system.
c) All drilling procedure and installation of casing and well head completions shall be in accordance with public laws.
d) Casing shall be set prior to installation of anodes to prevent damage to the lead wires.
e) Downhole components shall not be bundled or fastened with materials that will cause gas entrapment or backfill bridging.
f) The lead wire-to-anode connection resistance shall be checked before installation.
g) The lead wire insulation must be protected from abrasion and sharp objects. Prior to installation, lead wire insulation shall be visually inspected for flaws or damage.
h) Further assurance of lead wire insulation integrity may be achieved by conducting suitable wet tests using proper safety precautions.
i) 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 or connections.
j) The deep-well shall be either dry (closed hole) or wet (open hole) type as specified by design documents.
Notes:
1) When possible, the groundbeds shall be located at a minimum distance of thirty meters (30 m) from any buried metal structures.
2) Addition of salt to deep well groundbeds for the purpose of lowering the resistance of the groundbed is absolutely forbidden.
6.2.1.7.3.2 Closed well (closed hole)
a) Individual anodes shall be centered in the well with a suitable device that will allow passage of backfill material, will not entrap gases, and will not damage lead wire insulation or preclude proper placement of anodes. The installation details shall be as per standard drawing IPS-D-TP-713.
b) Before pumping backfill material, place all anodes at the predetermined depth and set the vent pipe from the bottom anode to the top of the well.
c) Before pouring or shoveling backfill material from the top of the well, displace the drilling mud with clear water, and place the vent pipe and two deepest anodes at their predetermined depth. Pour backfill material into the well to cover first anode, place the third anode, and repeat the procedure for each following anode.
d) Wetting the backfill material may be required to prevent bridging the well.
e) If strata resistivities permit moderate vertical shifting of anode position, the release of anode lead wire tension to provide slack may prevent excessive loading of the lead wire or the lead wire-to-anode connection in the event of caving or settling of the backfill material.
f) Type 3 coke breeze of IPS-M-TP-750: Part 2 shall be used as backfill unless specified otherwise by Company.
g) All deep groundbed installations (rectifier, well and venting location) shall be marked with adequate signs advising all personnel to vent the installation properly before commencing work and to keep fire away.
h) The use of one plastic vent pipe will aid in dissipating gases to the atmosphere.
i) The plastic vent pipe that extend below anodes normally have a series of small holes on 15 to 30 cm centers drilled in the immediate vicinity of the anodes. These holes shall be of such a
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small diameter as to prevent entry of the backfill material into the vent pipe.
j) The vent pipe shall be capped at both ends during the backfilling operation to minimize filling with backfill material or mud.
k) A threaded fitting installed at the surface end of the vent pipe will facilitate water or air injections which may be required to eliminate gas blockage. The use of a screened bushing on the threaded fitting will prevent entry of insects and foreign objects. The connection of a hose to the vent pipe with the end inserted in an open water container will provide a visible test of gas venting.
l) Vent pipes shall be located so as to preclude the entry of corrosive gases into the test box and rectifier. All lead wire conduits shall be sealed.
m)A uniformly low resistivity backfill (see f) shall be installed in the well until the top anode is adequately covered. Suitable backfill will decrease the anode resistance to the electrolyte, increase anode life, prevent caving, and facilitate gas venting. The remainder of the well shall be filled with a nonconductive, nonabrasive permeable backfill material (sand or pea gravel).
n) Backfilling may be accomplished by pumping, shoveling, or pouring. Backfilling method usually is determined by the characteristics of the strata and the backfill material used.
o) Presoaking of the backfill material with water is recommended to minimize the possibility of bridging. A wetting agent may be used.
p) Backfilling of wells containing drilling mud and/or water may be accomplished by pumping the backfill material (in slurry form) to the bottom of the well and allowing the well to fill from the bottom up to displace the drilling mud and/or water.
q) Observations of the change in anode resistance to earth shall be used to determine if the backfill material has been placed around the anode.
6.2.1.7.3.3 Open well (open hole)
a) Each anode shall be suspended, placed in position, raised, lowered, or removed for inspection by individual polypropylene rope (see IPS-M-TP-750: Part 10).
b) Anodes shall be centered in the casing, considering the required spacing between them, within the aqueous electrolyte as detailed in the standard drawing No. IPS-D-TP-707.
c) The final depth of the well will depend on the subsurface strata and the number and length of the anodes. The approximate depth shall be defined by the designer. Necessary precautions shall be taken to prevent deleterious modification of ground water quality.
d) Each anode shall be provided with an individual insulated lead wire or, a cable sufficiently long shall be connected to the anode-lead-wire with cable connector (line tap) and in-line (2 way) splicing kit (see IPS-M-TP-750: Part 11).
e) Each cable group of each deepwell shall be brought inside the positive test box (type 2) located at the deepwell head.
f) The test box shall be installed as per standard drawing No. IPS-D-TP-702 for individual termination of anodes and rectifier positive lead wires.
g) A shunt should be installed in each anode circuit to monitor the current output.
h) Resistors should be installed in individual anode circuits to balance anode outputs.
i) Sealing of anode wires to prevent capillary action between insulation layers may be necessary to prevent corrosive elements from entering the test box.
j) Sealing lead wire entry may be necessary to prevent entry of gases.
6.2.2 Installation of transformer/rectifier equipment
6.2.2.1 Transformer/rectifier(s) should comply with IPS-M-EL-155.
6.2.2.2 It is essential that the transformer/rectifier units will be installed by suitably qualified
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personnel and are installed in accordance with the requirements of National Electrical Code NFPA-70, Latest Edition and this Standard.
6.2.2.3 Manufacturer’s installation and operating manuals shall be available at site prior to installation of the transformer/ rectifier. The instructions contained therein shall be adhered to.
6.2.2.4 Air-cooled transformer/rectifier(s) shall be installed pole mounted by means of using four roll and plug type connectors and in a free place for cooling purposes.
6.2.2.5 Oil-cooled transformer/rectifier(s) shall be installed in non-hazardous areas and away from any equipment which creates heat.
6.2.2.6 Oil-cooled transformer/rectifier(s) shall be installed on a concrete plinth in accordance with the details specified by standard drawings IPS-D-TP-701 or IPS-D-TP-715 as required by the job.
6.2.2.7 Transformer/rectifiers shall not be installed in series or in parallel in the same cathodic protection circuit.
6.2.2.8 Transformer/rectifiers should be installed in non-hazardous area. If this is not possible, the construction of the rectifier units shall fulfill the requirements of the hazardous area classification applicable for the site.
Note:
When electrical work is carried out in hazardous areas requirement of IEC 79.14 shall be adhered to in conjunction with the area classification drawings and the following standards:
IPS-E-EL-110/1 "Area Classification and Extent".
IPS-E-EL-110/2 "Safe-Guarding in Hazardous Area".
6.2.2.9 If installed outdoors, the enclosure shall have a minimum degree of protection IP 54 in accordance with IEC 529.
6.2.2.10 Transformer/rectifier foundations shall contact tank support beams only.
6.2.2.11 Transformer/rectifier foundations shall allow space below the tank bottoms to permit painting.
6.2.2.12 If the proposed rectifier site is in an area where flooding may be a problem, the maximum high water level shall be ascertained and the transformer/rectifier mounted so that it will be above this level.
6.2.2.13 The transformer/rectifier shall be firmly secured to the plinth with holding down bolts to be supplied by the Contractor to the approval of the Engineer.
6.2.2.14 The transformer/rectifier manufacturer’s instructions shall be followed completely.
6.2.2.15 The ac and dc cabling shall be installed through steel conduits to connect the transformer/rectifier as shown on drawings IPS-D-TP-701 & 715.
6.2.2.16 The ac current cables and dc current cables shall be placed in separate conduits.
6.2.2.17 After the installation of cables the ends of the steel conduit shall be fitted with a suitable blanking disc and coated with water proof sealing compound (plastic inserts shall be used in conduit ends to protect cables).
6.2.2.18 The electricity supply shall be taken from the nearest existing electricity pole or a new one to be installed and brought to a pole mounted electricity meter by under-ground cable. The T/R unit shall then be supplied from this meter (see IPS-D-TP-701 and IPS-D-TP-715).
6.2.2.19 Before connecting the supply to the unit, it shall be checked that it is the correct voltage as stated on the rating plate of the transformer/rectifier.
6.2.2.20 The connections of dc cables to the transformer/rectifier must be mechanically secure and electrically conductive. Before the transformer/rectifier is energized, it must be verified that the
Dec. 1997 IPS-C-TP-820
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