I’m interested in feedback from those of you involved in pipeline maintenance or corrosion management.
My experience of Australian safety management studies is that when the threat of external corrosion comes up we say something like “It’s got factory applied linepipe coating, high quality joint coating, cathodic protection, regular cathodic protection monitoring, periodic coating defect surveys and periodic in-line inspection, therefore corrosion failure has been designed out and does not need any further consideration.” Nobody ever argues much against that position.
My question for you: Is this a bit glib?
Australian pipelines have a negligible rate of corrosion failures. Apart from about 15 leaks on one pipeline that was very poorly built and very poorly managed in the 1960s, the Australian pipeline incident database contains a mere two loss-of-containment incidents caused by corrosion, and both of those were stress corrosion cracking (including the infamous 1982 rupture of the Moomba – Sydney pipeline). So that makes the “designed out” conclusion look pretty reasonable.
In contrast, pipelines in North America seem to suffer corrosion failures at a great rate. A plausible (but unverified) explanation for the difference is that Australian pipelines are younger. Apart from the fact that they have had less time to corrode, they are also less likely to suffer serious coating failure because almost all Australian pipelines have been built since the development of modern factory-applied coatings. Many North American pipelines, on the other hand, are several decades old and were coated over the ditch with limited surface preparation.
For this reason pipeline engineers in North America pay a great deal of attention to evaluating the likelihood of corrosion failure. There is a variety of techniques available including a sophisticated reliability-based analysis (RBA). RBA has been done for a few Australian pipeline segments (as part of an APIA Research and Standards Committee project, which will be reported in due course). Interestingly, that analysis showed a small but non-zero probability of corrosion leak, notwithstanding all the design and operational features that we assume eliminates the risk (see footnote).
The main reason for the non-zero leak probability is the imperfect accuracy of monitoring, mainly in-line inspection tools.
With all that as background,
- Is it reasonable to say that we’ve “designed out” the risk of corrosion failures in the more modern Australian pipelines?
- Have there been corrosion failures (leaks) that were not reported to the incident database?
- Have you had any scary experiences of finding (by chance) unexpectedly severe corrosion despite a clean bill of health from in-line inspection?
- How do you think the AS 2885 safety management process could better address the corrosion threat?
- Is the AS 2885 process a suitable approach for assessing corrosion risk?
In asking these questions I’m not trying to cast doubt on the AS 2885 process as a whole, but rather probing and testing it for any possible weaknesses that we can correct if necessary.
Let me have your thoughts.
(Footnote: The RBA calculated probability of corrosion leak might be non-zero, but given that the consequences of a small leak are minor the risk is well within the tolerable range. There is nothing here to suggest that corrosion failure of Australian pipelines presents a serious risk to the public.)