A crack or breakage developing within gas turbine exhaust ducts can have a detrimental effect upon oil and gas production, as almost the whole platform needs to be shutdown should such a failure occur. Exhaust duct failure is particularly prevalent in the oil and gas industry, as the weight restrictions on offshore platforms means many of the components are made of lighter materials and thus are more susceptible to breakage. Due to this it is important to fully understand the risks, and look at the proactive processes to prevent them, rather than relying on reactive measures should such a breakage occur.

A failure within the duct can usually arise because from two sources:

• High cycle fatigue from flow induced vibrations
• Thermal fatigue from repeated starting and stopping of the gas turbine

This means that special attention to the process flow during design evaluation or troubleshooting of exhaust ducts can prove invaluable in preventing further accidents. Investigation and analysis is the best way to achieve this, although many firms don’t undertake both a structural and mechanical analysis.

What we understand at Lloyd’s Register ODS is that these two main issues may not be the catalyst for the failure, although on many occasions they are the only aspects to receive a full analysis. The problem is that other parts of this complex mechanism are left out or each aspect is inspected individually, which provides difficulties in understanding the combination of events. By undertaking three different forms of analysis; Structure analysis, fluid mechanical analysis and measurements, we are able to build an in-depth picture to help solve or prevent problems efficiently and to the highest standards.

It is now possible through technological developments and a high quality of expertise to conduct a coupled flow and structural analysis or fluid-structure interaction (FSI).

By using computational fluid dynamics to understand the complexity of the flow, these failures can be prevented in the first place.

As this provides a much more realistic idea of the loading on the structure than if these sections were to receive separate analysis, helping to prevent a failure rather than resolve it. This rigorous process saves companies both time and money, as well as vastly improving safety onsite.

As part of ODS we provide a combination of on-site investigation, measurement on existing or improved equipment (such as pressure, vibrations and temperature) and a range of advanced analytical methods. These processes need to be adhered to on a regular basis as standard within the oil and gas industries.

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.