Keeping pipe corrosion at bay

Ice floes are not the only threat to Arctic offshore infrastructure; pipework in the region is also extremely vulnerable to corrosion. Jennifer Pallanich discusses cold climate corrosion control techniques with NAC E International's Oliver Moghissi.

Most risks for offshore pipework in the Arctic are similar to risks elsewhere in the world, says Oliver Moghissi, VP and president-elect of NACE as well as DNV's director of the Materials & Corrosion Technology Center in Columbus, Ohio. The difference largely comes down to heightened political and environmental concerns, he adds, although 'there are issues with ice floes and when [pipelines] can be installed'.

Internal corrosion threatens pipework integrity, and NACE, established in 1943 as the National Association of Corrosion Engineers, has a lineup of technical standards to help prevent internal corrosion. Anti-corrosion technology can help, Moghissi notes, especially in environmentally sensitive areas like the Arctic. 'To do that offshore is sometimes difficult because internal corrosion is controlled by processing and treating the fluids, and that can be a challenge in a remote environment,' he adds.

That aside, removing water and acid gases like CO2 and H2S from the liquids can help. 'That lowers the risk of internal corrosion,' Moghissi says. An alternative is to inject chemicals. A third, more expensive answer, is to use a corrosion-resistant alloy. This option is less used, he says, because it also comes complete with its own construction and maintenance difficulties. Using a stainless steel or nickel alloy results in a high cost capex for materials but lower opex because chemical treatments and processing are not required, he adds.

Corrosion-resistant alloys are 'common in the North Sea, more so than in the US. That's an operating philosophy,' Moghissi explains. While the alloys reduced certain maintenance requirements, some of the materials 'became brittle' and posed other problems, he adds. 'The use of an expensive technology to reduce risk had an unintended consequence of increasing risk in another area.'

Ultimately the choice of corrosion prevention methods comes down to managing risk in terms of the return on investment. 'We can spend money on pipelines made of high nickel alloys, but they don't always reduce risk,' he says.

And risk management and risk aversion are different drivers. 'Every pipeline has a chance of corrosion,' Moghissi says. 'The risk of operating is never zero.'

Caring for the pipe over its life to manage risks – especially corrosion – is vital, he says, taking issue with the view of maintenance as 'inspect it and fix the damage you find'. While inspection is important, he says, 'it's like going to the dentist to figure out which teeth to pull'. Prevention is preferable.

Corrosion control technologies and risk mitigation technologies can reduce pipeline risks. To that end the NACE is currently updating its Corrosion Management of Pipelines standard. 'NACE right now is developing broader standards to outline the process of how corrosion is managed, including putting it into our context of risk,' Moghissi stresses. Whereas in the past there were a number of technical standards and the emphasis was on onshore pipework, the update – slated for release this year – will be applicable for offshore as well.

One potential hitch in pipeline development revolves around the so-called communication gap between the corrosion engineer and the generalist – in most cases the project manager or operations manager – so NACE's update will work to ease that as well by using risk as a common language on which to make decisions, he says.

The association, which now has about 25,000 members, is looking to involve all stakeholders in defining its standards. 'Instead of just talking to ourselves, I hope we start talking to people outside of our community, because these are the guys making decisions about corrosion management.'

Because the corrosion community 'tends to be very insular', Moghissi says, 'we have a very deliberate strategy to talk to non-technical stakeholders' like the government and media as well.

He believes the Macondo disaster will have far-reaching implications. 'We should expect a whole new regulatory regime for offshore pipelines,' he says. 'The fear – at least among the technical community – is that regulations will roll out and they'll be overly prescriptive.' Prescriptive regulations can be 'artificial constraints' that 'impede the use of new technology', he says. The concern, he adds, is that a NACE standard includes a particular new technology, but that the regulations are too prescriptive to allow its use.

The hope, Moghissi concludes, is that any new regulations for offshore pipework will include NACE technical standards by reference. OE

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