Sour service fluids from wells place significant demands on pipeline material, particularly in deeper water.
This can present major technical and financial challenges for pipeline operators as the fluids can cause fractures and cracks which affect pipeline performance and reliability. DNV GL has now launched a Joint Industry project to develop a methodology to evaluate fractures and cracks using a Single Edge Notched Tensile (SENT) test designed specifically for sour service environments. Eight participants are on board and the JIP is still open for new participants.
A pipe material and weld that performs well in air will be significantly less tough and resistant in a sour environment. A SENT test is designed to simulate loading conditions and crack depths similar to those experienced by pipelines operating under normal conditions. Research conducted in DNV GL’s laboratories shows that in a sour environment, where fluids such as H2S, H2O and CO2 may be present, results can be highly variable depending on numerous environmental and test parameters. Fracture toughness, for example, tends to decrease with increased H2S concentration (partial pressure of H2S) and decreased loading or strain rate. Current guidance under DNV-OS-F101 and DNV-RP-F108 does not reflect this.
Dr Jens Petter Tronskar, DNV GL Vice President and CTO of the Deepwater Technology Centre in Singapore, says: “Sour gas is evident in various oil and gas producing regions of the world, in particular, the Middle East and the Commonwealth of Independent States. The JIP will involve detailed experiments and analysis to provide a better understanding of the key parameters known to impact fracture toughness test results. This will enable the development of a guideline which may further develop into a Recommended Practice which will provide significant technical, logistical and financial savings to the industry.”
The JIP is a joint effort between DNV GL Singapore Deepwater Technology Centre and DNV GL’s laboratories in Singapore and Columbus and will be run in three phases over two years.
“This project is a good example of how DNV GL utilize our global network of advanced testing instruments and experts to enable efficient operations and fast technology implementation. By providing a neutral ground for cooperation, we facilitate collaboration across companies that helps solve industry challenges, ” says Elisabeth Tørstad, CEO DNV GL Oil & Gas.
The Columbus laboratory is also carrying out an ongoing JIP to develop best practice guidelines for performing sour service Engineering Critical Assessments (ECA), scheduled for completion in December 2015. This JIP includes fatique crack growth rate and fracture toughness tests conducted in a wide range of sour environments. The findings from the study will complement the new JIP to develop a sour service SENT methodology. “Performing different SENT test methods on steels in sour environments will be hugely beneficial when performing Engineering Critical Assessments (ECA),” adds Dr Tronskar.
