Hydrogen Enhanced Cracking (SSC, HIC, CF) of Tubulars and Pipelines for Sour Service in Deepwater and Seabed Applications
Authors: Walters Matthew , Dent Phil , Doyle Richard , Fowler Chris , Connolly Brian J , Horspool Dean 
Published: June 2014

New technologies and associated materials advancements are required for installation of platforms, umbilicals, risers, and subsea pipelines in severe, deepwater environments. Two on-going research programmes that investigate hydrogen enhanced cracking susceptibility of material for these applications are presented. In the first part of the paper the development and application of a high temperature high pressure corrosion fatigue facility to investigate the susceptibility of flexible pipeline components in sour environments is described. Structural integrity of the load supporting armour wires within the flexible pipe remains a concern. Such armour wires are susceptible to hydrogen embrittlement in the presence of H2S, which significantly reduces fatigue life. To simulate complex environmental conditions inherent to such challenging production locations, servo-hydraulic machines capable of testing to 50bara and 100ºC in simulated oilfield environments have been developed and installed into a state-of-the-art facility. This facility has enabled investigation of fatigue-life properties over a wide range of service environments and the data generated has contributed towards the technological advancement of flexible pipelines and risers. The second programme described presents an investigation of the effect of seabed temperature on the sulphide stress cracking (SSC) resistance of weldable martensitic stainless steels (WMSS). WMSS are used for mildly sour flow-lines as an alternative to inhibited carbon steel or lined pipe. For most selection and qualification programmes for sour applications the material is tested in accordance with NACE MR0175 at maximum design temperature and at ambient temperature. However WMSS may be more susceptible to SSC below ambient temperature and current information in the literature is limited. Consequently qualification to the NACE standard may show acceptable results, whereas in-service cracking could still occur. It should be noted that for sub-sea pipelines the typical seabed temperature is in the region of 4°C, which may be experienced during ‘shut-in’ conditions. SSC testing has been undertaken on parent WMSS line-pipe at ambient and seabed temperatures in simulated condensed and produced water at two partial pressures of H2S. Test results are presented and the SSC performance of the material is discussed with consideration to test temperature, pH, H2S partial pressure and specimen surface condition.

Introduction (PartA)

Increasing demands for fossil fuels throughout the developed and developing world has promoted the Oil and Gas industry to implement recovery strategies to oil reserves once thought to be economically unviable. These ‘new’ reserves are typically located offshore in deepwater (400–1500m) and ultra-deepwater (&gt;1500m) fields. New technologies and associated materials advancements are required for installation of platforms, umbilicals, risers, flowlines and subsea pipelines in these severe, deepwater offshore environments. According to the International Energy Agency estimates of known reserves located in such waters range from 160bn to 300bn barrels. Most of these reserves are in the waters of Brazil, Angola, Nigeria and the US and progress towards extracting these reserves has been surprisingly rapid. Ultra-deepwater production only began in 2004 and has reached 200,000 barrels per day in 2012. This number is only set to continue with huge investment in offshore facilities such as the $500m Dalian Pioneer, the biggest offshore rig yet, currently under construction in China's Liaoning Province which is capable of safely operating in waters up to 3048m deep. The development of flexible pipelines and risers has played a major role in enabling such rapid progression. Installation of these dynamic production components has been essential in allowing the Oil and Gas industry to develop fields in deeper and deeper waters, utilising floating production technologies (Figure 1).