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مدیر وبلاگ : pc7a
نویسندگان

          Installation of Magnesium Anodes

           The Magnesium anodes of  this project are used for three important job:

          - Cathodic Protection of Crossed Casings    

          -Temporary Cathodic Protection of  Pipeline

          -As some measures of AC Mitigation of pipeline parallel with AC owerhead line

          Magnesium Anodes using for above subjects  are prepackaged in suitable backfill and cotton bags with different weights , The shape of anodes are as below:


     1.1.  Magnesium Anodes shall be installed according to design specifications and drawings.

    1.2. Before anode is buried, it is important that any waterproof wrapping material be removed.

    1.3. Typical galvanic anode installations shall be of the following types:

1.3.1 Single packaged anode

1.3.1.1 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.

Same as drawings and below schematic (feature 1)

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1.3.1.2  In congested sites where space limitations are extremely critical and  there is not enough distance (at least 1.5 m ) from the pipeline  ,the 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 1.5 meter below the pipeline

      Same as drawings and below schematic (feature 2)

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1.3.1.3 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).

1.3.1.4 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.

 

1.3.2  Multiple galvanic anodes

Anodes shall be installed according to design specifications and drawings.

Before anode is buried, it is important that any waterproof wrapping material be removed.

Multiple galvanic anodes system is also designed in this project . Same as drawings and below schematic (feature 3)

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1.3.2.1 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.

1.3.2.2 A Parallel line of magnesium anodes shall be about 5 meters away from the pipeline,

1.3.2.4 As per attached drawings each anode cable distinctly come to box , it will then be possible to observe the current output of all MG  anodes as they are connected ,and after installation.

1.3.3 Connection of galvanic anodes to pipeline

1.3.3.1 for features 1 and /or 2  ,The anodes can be directly connected to pipeline  (see above schematics ) but for feature 3 (multiple or cluster ) shall be  using the anode junction box. (see above schematics ) 

1.3.3.2 Anode lead wire shall be separately  connected to anode junction box and using  sized split bolt (line tap) or compression type connectors splicing kit is not recommended .

1.3.3.3 Termite welding (cad welding process) shall be used to connect the anode lead wire to the pipeline. The detail stages of Termite welding is attached in drawings.

1.3.3.4 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.

1.3.3.5 All connections must be permanently low resistance. Any gradual development of joint resistance can reduce anode output

1.3.3.6 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.

1.3.3.7 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.

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1.4 Installation of Permanent Reference Electrodes

            Permanent Reference electrodes shall be installed according to design specifications and drawings.

Before permanent reference electrodes are buried, it is important that any waterproof wrapping material be removed.

  1.4.1 Permanent reference electrodes shall be installed immediately prior to construction.  

1.4.2Permanent reference electrodes shall be installed   between 500 to 1000 mm distance from      pipeline as per attached drawings

1.4.3 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.

        1.4.4 Permanent reference electrodes shall be installed   between 500 to 1000 mm distance  

         from pipeline as per attached drawings

 1.4.5 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.

1.4.6 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.

   1.4.7 The actual location of permanent reference electrodes and cabling shall be accurately       

  documented on the as-built drawings.          

1.5 Installation of test stations (test points)

1.5.1 The cathodic protection test points shall be installed 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.

Care shall be exercised to avoid damage to structure coating during excavation and backfill.

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1.5.2. Test points shall be installed not more than 2.5 m away from the pipeline.

1.5.3 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.

1.5.4 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.

1. 5.5 The test lead connections shall be properly bonded to the structure by Termite-welding process.

1.5.6 The Termite-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.

1. 5.7 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.

1.5.8 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.

1. 5.9 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.

 

. 1.6TERMITE WELDING OF CATHODIC PROTECTION LEADS

         1.6.1The connection of cathodic protection wire leads to new or in-service carbon steel pipelines under pressure shall be done by Termite welding .

          1.6.2Connections to pipe less than 3 mm thick shall be made using approved clamps or silver soldering.

 1.6.3Termitee weld process shall be applied only by skilled experienced field personnel.

 1.6.4The minimum distance of a Termite weld from a circumferential weld shall be 200 mm.

1.6.5The minimum distance of a Termite weld from a longitudinal weld shall be 40 mm.

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 1.6.6In attaching one wire to a pipeline only one charge shall be used. If the first Termite weld does not take, a second Termite weld shall not be attempted on the same spot.

If a Termite weld is disapproved on the first charge, it shall either be removed, the surface cleaned to bright metal and the process is repeated or a new location on the pipe is selected.

          1.6.7Termite welds shall not be attached to pipe wall thicknesses less than 3.18 mm while the pipeline is pressurized.

 1.6.8The connection of leads to high pressure gas lines with wall thickness less than 4.78 mm, but more than 3.18 mm by Termite welding shall be done with the gas flowing.

 1.6.9The use of Termite welds shall be avoided in high stress areas such as elbows, tees, etc.

 1.6.10If more than one weld is required such as two adjacent wires or large conductor split in two to get the required size for a 15 gram charge, the spacing between point of connection shall not be less than 100 mm (4 inches).

 1.6.11Pipe Preparation

1.6.11.1 1.6.11.1The pipeline coating shall be completely removed including primer and the pipe cleaned with a file to white metal. The pipe shall be completely dry.

 1.6.11.2The wall thickness of the pipe shall be checked using a portable ultrasonic wall thickness tester and the permissible pressure of the line checked.

 1.6.11.3Where possible Termite welds shall be applied to horizontal pipes.

 1.6.12Termite pipeline Weld Preparation and Procedure

1.6.12.1Care shall be taken to ensure that the graphite Termite weld mold is completely dry and free from slag or other impurities before proceeding with Termite welding on pressurized pipelines.

 1.6.12.2The copper conductor shall be clean and dry and the insulation cut back sufficiently for insertion into the mold.

 1.6.12.3The copper conductor shall be wrapped around the pipe at least once and enough slack provided to allow for pipe in soil movement.

 1.6.12.4The Termite pipeline welding shall be done in accordance with the steps indicated in the IPS drawing No. IPS-D-TP-702.and or attached drawing

  1.6.12.5After the completion of the Termite pipeline weld on buried pipelines, the bright metal

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surfaces shall be protected and covered by the application of a P.E. tape & primer and a "Royston Handy Cap" or equal. The "Handy Cap" shall be taped in place using primer and cold applied self adhesive P.E. tape to provide a watertight seal on all exposed steel and copper surfaces.

The tape shall overlap existing pipe coating to about 25 mm (1 inch) minimum.

Manufacturer’s instruction for application of "Handy Cap" shall be rigidly followed.

 

1.      TESTING AND COMMISSIONING PROCEDURES

2.1PRE-COMMISSIONING

All pre commissioning checks should be done prior to the energisation of the system.

The pre commissioning shall proceed as follows:

2.1.1  Visual check of boxes and terminals

2.1.2  Check the installed permanent cu-cuso4  reference electrode by using a portable   cu/cuso4 reference electrode

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 2.1.3.      Measurement of  pipe to soil potential due to 6 potential test boxes in site

2.1.3.      Measurement of anodes potential before connecting to pipeline ,by using a portable cu/cuso4 reference electrode  ,this potential named open circuit anode potential

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   c2.1.5  Event & Analysis

    Event 1:

If potential of  pipe with respect to  permanent cu-cuso4 installed in each test point is between 300 to 650 milivolts ( natural potential of carbon steel pipe in soil ) :

    Analyze ;

1-      Termite pipeline  pipeline welding and cable of pipe is correct

2-      Permanent reference cell is connected and operated

     Event 2:

If potential of  pipe with respect to  permanent cu-cuso4 installed in each test point is near zero or less than 250 milivolts  ( natural potential of copper in soil ) :


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Analyze ;

 1-  Termite pipeline welding and cable of pipe is disconnected

2-   Permanent reference cell is not operated or disconnected

Note :

In event 2 With using one portable reference electrode ( equipment 6.2 ) instead of doubt permanent reference cell and measuring potential between pipe terminal in TP and this portable reference we can find that  Termite pipeline weld is disconnected and/or permanent reference cell is failed such that :

 

 

 

1-If potential of pipe with respect to  portable reference cell were between 300 to 650 milivolts then : permanent reference cell is failed

2--If potential of pipe with respect to  portable reference cell were under 250  milivolts then : Termite pipeline welding to pipe is failed

 

 

 

 

1.1.     COMMISSIONING

After connecting anodes to pipe  and let minimum 12 houres to pipeline polarization and ,during the commissioning period the following activities should be under taken  by the commissioning engineer

2.2.1        ON potential measurement of 6 potential test boxes after MG anode connected to pipeline


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The measured potential in all potential test boxes should be in one satisfactory ranges

      The ON potential criteria for this project as per IPS –E-TP-820 and paragraph 5.4 of design 

      Document should be as follows: 

 

-950-1500mV With respect to CU/CUSO4 reference electrode for pipelines have been accepted as protection criteria in this project.

 

 

 

2.2.2 -check and record all MG anodes current in cluster type anode beds ,for assurance of anode operation after connection to load (pipeline )


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      2.2.3Event & Analysis

Event 1 :

If anode current is higher than 100 mA or more than this amount:

Analyze :

Anodes are in suitable operation

Event 2 :

      If anode current is less than 50 mA  or near zero

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