In more ways than one, a ticking time bomb of corrosion is hidden in the transit of pipes through bulkheads, decks and deckheads on offshore facilities. Ian Cordingley reports.
The danger of corrosion is not only hidden from sight, but also often from mind, as these all-important offshore fixtures are typically considered to be ‘fit-and-forget’ with the fitting or replacement seen as the end of the inspection and maintenance process. This brings the temptation to place the matter of inspections in a low priority category, and that can be exceptionally dangerous.
The term ‘Transits and Penetrations’ describes the fixtures that allow a service or utility, such as a pipe or cable, to pass from one discrete area of a plant to another. In some instances the purpose of the fixture is to maintain containment and separation between areas. Fire-spread, toxicity or water ingress are all valid reasons to seal one area from another.
Having inspected and examined a large number of such processes, we have found that in many instances plant operators believed they had a safe facility, free of corrosion or the risk of such decay. In reality close inspection demonstrated some very worrying results, on transiting pipework in particular.
These have included crevice corrosion, scale and pitting, waisting (wall thickness loss around a pipes girth), dissimilar metal corrosion, gasket failure, (CUI) corrosion under insulation and, on many aged transits and penetrations, missing, un-insulated, or badly-fitting bands and gaskets. On some mature plant we have seen 13 per cent of high criticality pipes with an external corrosion condition beyond that considered acceptable by the operators.
When the attachment of clamps, seals and bolted fitments to coated pipes is a requirement then the potential for mechanical or coating damage is obvious. The resulting possibility of a corrosion point increases further when the substrate is then locked away from view for the lifetime of the seal.
Even those seals which appear in excellent condition from the outside – perhaps they have been painted in the last maintenance round – are in danger. Just because a seal is seen as ‘fire-safe’ it doesn’t mean there isn’t still a danger of degradation from atmospheric or other contamination
We have experienced many instances where a pipe penetration seal has looked in sound condition, only to find that the corrosion of the fittings, or the transiting pipe, has undermined or even totally destroyed the integrity of the seal.
As with CUI, there are few opportunities for such hidden failures to be noticed without removing the transit or seal, which covers and hides the substrate.
An acknowledgement of the challenges of transits and penetrations is beginning to develop however a lot of education is still needed if these important fixtures are to be kept safe.
Even once the issue is recognised, we are only at the beginning of the logistical and mechanical struggle. As well as the potential for financial constraints to sidetrack essential maintenance plans, most plants have hundreds, if not thousands of transits and penetrations, giving the process of checking for problems a scale which makes planning hugely important.
Additionally, safety concerns must be clearly defined and factored in. To inspect the pipe, there must be an element of dismantling of the fixtures and seals, and, where the fixtures purpose is fire protection, water ingress or toxicity containment, there is an additional cause for concern. In some cases, upwards of ten seals may be open at any one time and the potential for any negative impact upon plant safety must be minimised.
In order to begin to mitigate these challenges facility managers need to prioritise some very basic criteria to feed into their strategy including criticality of the pipework, time since last inspection, temperature ranges and cycling, insulation, coatings, substrates, and a number of other factors.
This can then be integrated and scheduled in the wider maintenance programmes or through an effective toolkit such as Strategic Corrosion Management’s RISCm package.
Our 360integrity framework enables a far more integrated approach to corrosion, integrity and maintenance execution than is currently available elsewhere. The heart of which is RISCm and it not only maintains the traditional disciplines of Integrity and Fabric as separate entities, but also handles all of the data integration and presentation necessary, so from a management stand point, it’s all in one useable box of data.
Understanding of the situation regarding transits and penetrations is growing. There are a number of asset managers who are already aware of the potential problems and have in place robust, logical and very efficient regimens to mitigate these challenges. In some cases, we have supported these managers in integrating the control of transits and penetrations into their overall corrosion management strategy.
However, for all of us it is vital that fit-and-forget becomes a phrase which triggers alarm bells. Yes, a transit and penetration may well achieve its lifecycle without trouble, but the potential for problems, or worse, catastrophic failure is clearly too big a risk to take.
Ian Cordingley is Managing Director of Strategic Corrosion Management, Crosland Park, Northumberland, UK. www.stratcorrman.com