The Relentless nature of Corrosion

Article published in The Regulator | Issue 1: 2020

The hostile environment typically faced by an offshore facility, and the very nature of its operations, lends itself to corrosion. It is a persistent threat to the integrity of an offshore facility and therefore the safety of the offshore workforce, and must be continually managed from the construction yard to decommissioning.

It is a common assumption that corrosion is only a concern for ageing facilities, but this is not the case. In fact, NOPSEMA has identified corrosion at a number of new facilities.

For example, a recent pipeline inspection found up to a 19 per cent loss in wall thickness within two pipelines in the first years of what will be decades of operation. The wall loss was thought to be the result of inadequate corrosion mitigation during a long preservation period (the time between construction and the introduction of hydrocarbons). Given its location, this corrosion cannot be reversed or remediated, so the only option is ongoing vigilance. While the pipelines remain fit-for-service at their maximum allowable operating pressure, they will require enhanced inspection and monitoring, at significant additional cost, to ensure they remain safe for their operational life.

Historically, corrosion has been the cause of a number of catastrophic pipeline failures. In Western Australia, in 2008, a 12 inch high pressure export sales gas pipeline ruptured on Varanus Island. The outflowing gas ignited resulting in an intense fire which destroyed a nearby pipeline directing further fires toward the onshore processing plant and causing two more pipelines to rupture and ignite resulting in A$60m of damage to the gas processing plant. Fortunately, no one was injured but the resultant restriction in gas supply lasted over a year and is estimated to have cost the Western Australian economy around A$3bn. The failed pipeline had been corroded to such an extent that it could no longer contain the pressure. The report into the incident found that the pipeline had ineffective anti-corrosion coating and cathodic protection, and that the petroleum company had inadequate inspection and monitoring programs. With ageing facilities, corrosion can be pervasive and when it takes hold the difficulty and cost to recover and demonstrate the ongoing integrity of the facility increases exponentially.

Recently, NOPSEMA prohibited hydrocarbon production at an ageing facility where the topside structures were degraded to such an extent there was an increased risk that structural elements could fall onto process pipework causing a major hydrocarbon loss of containment or crush any personnel working underneath. NOPSEMA inspectors documented many significant corrosion defects and found that the responsible petroleum company’s failure to identify and rectify these defects posed an immediate threat to the health and safety of the offshore workforce. There are no guarantees that hydrocarbon production at the facility will recommence.

Corrosion is one of the biggest threats to facilities within the Australian offshore petroleum industry. However, the implementation of an effective whole-lifecycle integrity management system can control this threat. NOPSEMA strongly encourages the industry to challenge the temptation to defer inspection, monitoring, maintenance and repair in favour of construction project deadlines, production and profit. Guidance for corrosion management in oil and gas production and processing is available from the Energy Institute at https://publishing.energyinst.org/.