PROCEDURE 15
These procedures are commonly practiced when electrical interference causes or threatens to accelerate corrosion og buried or submerged assets.
INSTRUMENTATION
- Holiday detector
- MATERIALS
- Cadweld or similar approved jointing kit.
METHOD
15.1. Direct bonding.
15.1.1. Excavate each of the pipelines that are interacting.
15.1.2. Expose the pipe metal on the top of each pipe.
15.1.3. Clean to bright steel.
15.1.4. Attach a low resistance conductor to the pipe metal by a method approved by the operator.
NOTE. The most common way is to use thermo-weld (cadweld) where a mold is placed over the conductor and bright steel, filled with a brazing powder which is spark ignited to make the joint. There are many situations which make this method unacceptable and conductive epoxy joints, clamps and an assortment of welding techniques have been used.
15.1.5. Label both ends of the conductor with the identity of the pipeline.
NOTE. The method of labelling should be resistant to the environment.
15.1.6. Photograph or sketch the exact position of the joint, while the excavation is open.
15.1.7. Clean, prime and recoat the pipeline and joint.
15.1.8. Test the insulation using an approved 'holiday detector' and wire brush attachment.
15.1.9 Back fill the excavation, making sure that the conductor rises to the surface directly above the joint.
NOTE. At this stage the two cables will be at ground level above their respective joints.
15.1.10. Trench the conductors to a location approved by the operator of each pipeline.
15.1.11 Photograph or sketch the trenches while still open.
15.1.12. Label each conductor with the identity of it's pipeline at 1m intervals.
15.1.13. Thread the two conductors through a standard cathodic protection test post
15.1.14. Terminate each conductor on an insulated board.
15.1.15. Label each terminal.
15.1.16. Measure and record the current and polarity between each terminal.
15.1.17. Fit a low resistance connection between each terminal.
15.1.18. Set the test post and secure according to the pipeline operators specification.
15.2.
15.2.1 Carry out procedures 15.1.1. to 15.1.14.
15.2.2. Attach a variable resistor to each terminal.
15.2.3. Set up a measuring procedure at each pipeline according to the specifications of the operator.
NOTE. This could be according to any of these procedures, for example any of Procedures 1, 5, 10, 11, 12, or 13, and there may be other techniques for measuring the particular criterion required by a pipeline operator.
15.2.4. Link each of the variable resistors to a common buzz-bar.
15.2.5. Adjust each of the variable resistors to a level which allows each pipeline to reach its operators criterion.
NOTE. It will be found that this alters the balance the remainder of each operators cathodic protection system. In which case it will be necessary to adjust each system and repeat 15.2.1. to 15.2.5. It is often found that it is not possible to attain every operators criterion.
15.3.
15.3.1. Carry out procedure 15.1.1 to 15.1.12.
15.3.2 Excavate to allow one sacrificial anode for each pipeline with a 50mm gap between each, to be positioned midway between the subject pipelines.
15.3.3. Place the pre-packed sacrificial anodes side by side on a 250mm deep bed of conductive carbonacious backfill in the trench.
15.3.4. Photograph or sketch the arrangement before back-filling.
15.3.5. Cover with a further 250mm of conductive carbonacious back-fill before backfilling the excavation completely.
15.3.6. Make sure that the anode conductor lead rises to ground level immediately above the anode bed.
15.3.7. Place a groundbed marker in position directly above the anodes as specified by the pipeline operators.
15.3.8. Extend the anode tails with sufficient cable to reach the designated test post position.
15.3.9. Trench the cables to the test post labeling every 1m. "Sacrificial Anode"
15.3.10. each together with the cables from the pipelines.
15.3.11. Terminate each conductor on an insulated board.
15.3.12. Label each terminal.
15.3.13. Measure and record the current and polarity between each pipeline and it's respective sacrificial anode.
15.3.14. Fit a low resistance connection between each pipeline terminal and it's respective anode terminal.
15.3.15. Set the test post and secure according to the pipeline operators specification.
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