Subsea Pipeline - HSS disbondment - CP shielding
Subsea Pipeline - HSS disbondment - CP shielding
(OP)
During recovery of an installed pipeline it was noted that there had been some disbondment of some of the Heat Shrink Sleeves (HSS) at the field joints. This had led to some seawater entrapment, which could have potentially been in contact with the steel. As the HSS are noted for their high di-electric properties I understand that there is the possibility of Cathodic Protection (CP) shielding so the location of entrapped water could start to corrode as it is no longer protected by the CP system (sacrificial anodes).
I have a few questions that I can not readily find the answers to and would be grateful for some help with:
1. Is there any way that once the Oxygen 'runs out' in these areas that the oxygen could be replenished?
2. If it can be replenished does that mean that the same mechanism that replenishes the water will mean that the CP is also 'flowing'?
3. Once the oxygen runs out (and it is not replenished) then does acid corrosion or bacterial corrosion 'kick in', or does the corrosion mechanism then stop altogether?
4. If it stops then how do you calculate how what damage has occurred?
5. Is there any non-destructive way of finding out if the field joints that have not been cut back are affected the same way?
6. Is there anything retrospective that can be done to help this?
I have a few questions that I can not readily find the answers to and would be grateful for some help with:
1. Is there any way that once the Oxygen 'runs out' in these areas that the oxygen could be replenished?
2. If it can be replenished does that mean that the same mechanism that replenishes the water will mean that the CP is also 'flowing'?
3. Once the oxygen runs out (and it is not replenished) then does acid corrosion or bacterial corrosion 'kick in', or does the corrosion mechanism then stop altogether?
4. If it stops then how do you calculate how what damage has occurred?
5. Is there any non-destructive way of finding out if the field joints that have not been cut back are affected the same way?
6. Is there anything retrospective that can be done to help this?





RE: Subsea Pipeline - HSS disbondment - CP shielding
Its doubtful that you will do any more damage than making a very fine coating of top surface rust which will stop further corrosion from occurring underneath it.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Subsea Pipeline - HSS disbondment - CP shielding
The use of abrasive blasting, with primer as a third layer of defence, is favoured to address the latter failure mode in shrink sleeves.
ILI will be the only effective way to pick up any ensuing corrosion problems.
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Subsea Pipeline - HSS disbondment - CP shielding
SJones - good clarification, part of my confusion was getting my head around the fact that if there is water flow then how can there be no conductive path - thanks for helping me with my sanity. ILI (in-line inspection, I presume?) sounds like it may be a good idea but as the pipeline is only recently laid I suspect that there won't be much change from the baseline intelligent pig runs as yet, or indeed any differences that may be found could well be put down to inaccuracies in the ILI technique, especially as any corrosion that has taken place already will be at very localised areas.
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Brilliant guys - responses from 2 of the best first time up...thanks again.
RE: Subsea Pipeline - HSS disbondment - CP shielding
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04