Gas turbine exhaust ducts are key components in the oil and gas industry, with failures can being catastrophic in terms of both safety and production. A failure of an exhaust duct usually means that as the walls crack, hot exhaust gases burn through the insulation, or large parts of the duct section are removed. These failures can arise because of the pressure to decrease weight and size due to their location offshore, coupled with the necessity to rectify the problem as quickly as possible, as production suffers from having a non-functioning piece of equipment.

The immediate problems which can arise from such failures are:

• Damage on duct walls, cracks, missing insulation.
• Waste Heat Recovery Unit (WHRU) failure, exhaust gas leaks, silencer degradation.
• Emergency shutdown, loss of production.

These of course, can cost time and money, as well as the potential cost of lives.

Because of this it is important to fix the problem as quickly and as efficiently as possible. One such way is through crack mitigation. By drilling small holes at the edge of the crack it prevents it from propagating, although this won’t last for an extensive period of time. The key problem with this commonly used technique lies in the simple fact that you haven’t identified the root cause. By making intermediate solutions to keep production running you pave the way for bigger and potentially more catastrophic problems further down the line.

Prevention is better than a cure

We at Lloyd’s Register ODS believe that the best way to prevent these failures is to understand the risks and processes involved, when manufacturing oil and gas on off-shore platforms. We have paid particular attention to the problems which arise from weight restrictions as parts are made as small and light as possible, such as the exhaust collectors making the flow very difficult to manage. Through our up to date, technical software and methodology we are able to measure the flow and develop ways to prevent these failures (of which I will expand in my upcoming blog). But we also understand that if such a failure should occur, the best solution is to prevent the problem from happening again.

One such example of this can be seen in the failure in 2006 of a gas turbine exhaust duct on Åsgard B floater in theNorwegian Sea, on this occasion a rupture the size of an A4 piece of paper occurred. This can potentially be a high risk situation, because as soon as this equipment fails you have the potential of hot exhaust gasses, reaching up to 500 degrees C leaking out on a platform that’s producing flammable liquids and gasses, which is clearly a safety problem. Not only because of the immediate exhaust gases hitting someone but also the possibility of igniting other gasses. Our approach was to identify the root cause and fix it as quickly and efficiently as possible to prevent such a problem re-occurring. Since then the floater has been producing 14million cubic metres a day.

At Lloyd’s Register ODS we understand that sometimes these failures are unavoidable and so the next best step is to rectify these problems with minimum risks to safety and production. Possessing the highest grade technology and technical expertise is essential to minimise the potential risks.

I’ll be presenting on gas turbine exhaust ducts at Offshore Europe 2011.

Come along to stand #2C100, or follow us through this blog or on twitter if you can’t make it in person.