TWI shows expertise in corrosion security, investigation and assessment
One instance of this noticed TWI referred to as by the Kuwait Oil Corporation to search out the foundation reason behind failure in a vital high-pressure moist bitter service fuel pipeline. The pipeline had suffered a number of leaks, together with one as a consequence of a crack alongside a spiral weld, nonetheless restore uncovered extreme inside corrosion which brought about the pipeline to be decommissioned. TWI was referred to as to undertake a failure investigation, however preliminary checks discovered that the pipe materials had been accurately chosen and the surface of the pipeline was in good situation, indicative of efficient coating and cathodic safety.
However, the within of the pipeline confirmed extreme pitting in the underside of the pipe alongside a spiral weld failure. Phased Array Ultrasonic Testing confirmed that the cracking originated internally and was longer on the within than on the surface. This inside corrosion had been attributable to the presence of water, CO2 and H2S gases, in addition it was discovered weld misalignment had resulted in roof-topping of the spiral weld, which elevated the in-service stresses, whereas common pipeline shutdowns added a small quantity of cyclic loading. While none of those components would have created the issues on their very own, when mixed they had been sufficient to trigger the cracking. TWI decided that elevated localised stress on the spiral weld together with corrosion as a consequence of a extreme bitter service setting brought about the cracking. As a outcome, the Kuwait Oil Corporation changed their pipeline with a seamless bitter service pipe rated to the proper degree of H2S and water minimize. You can find out more about this incident of failure along the spiral welds in this gas pipeline right here.
This just isn’t the one incident that TWI has investigated on behalf of the Kuwait Oil Company, as inside blistering on a 20” diameter cross-country pipeline created the necessity for a fitness-for-service assessment. In this occasion, TWI was despatched a 200mm lengthy specimen of the longitudinally-welded broken pipe together with an undamaged spirally welded part from the identical pipeline. Both damaging and non-destructive checks had been undertaken on the pipes in order to find out materials property and establish the trigger and extent of the injury. The outcomes of those checks would enable the Kuwait Oil Company to undertake in-line inspections to evaluate the fitness-for-service of their pipeline as an entire. Tests included ultrasonic testing, magnetic particle inspection, tensile, hardness, and toughness checks, along with chemical evaluation and metallography. Meanwhile, the working historical past of the pipe revealed that laminations and blistering had created failure in 1976 and that the pipe had briefly been used to move seawater for fire-fighting following the Gulf War of 1991.
An inspection report from 1981 was assessed, though it was unclear whether or not suggestions for restore had been actioned at the moment, whereas in-line inspection discovered inside corrosion injury was virtually solely absent from the 7km of spiral welded pipe however was widespread in the long-seam welded pipe that comprised the remainder of the pipeline. Test outcomes confirmed that the long-seam pipe contained hydrogen induced cracking and blistering alongside inside corrosion, resulting in the conclusion that the spiral welded pipe had been put in later. However, the long-seam pipe had failed as a result of transport of a bitter product, most certainly earlier than the 1976 failure, whereas the transport of seawater in 1991 had little impact, if any. Since the Kuwait Oil Company confirmed that the longer term working strain of the pipeline could be very low, TWI was in a position to suggest another revalidation methodology for the pipeline, based mostly on a hydrostatic proof check. This saved considerably on the price of inspection and restore, whereas making certain the continued security and integrity of the pipeline. You can find out more about this pipeline fitness-for-service case right here.
It isn’t just in the case of failure that TWI is named to help, as demonstrated by a case involving Single Buoy Moorings (SBM) of Monaco. SBM had been tasked with designing and constructing an offshore floating manufacturing, storage and offloading (FPSO) vessel for use off the coast of NW Australia. However, through the pipework welding, excessive hardness values had been found in the weld zones for the duplex stainless-steel inflexible arm and riser piping. As these hardness values had been exterior the design necessities, the welds had been despatched to TWI for analysis.
Simulated setting checks had been performed utilizing sluggish pressure price (SSR) tensile testing and four-point bent beam checks at elevated temperature and strain in a scorching, bitter brine resolution. These checks confirmed that whereas there have been excessive hardness values associated to the pressure induced by welding, these had been unlikely to be an issue throughout service, that means that the welds had been handed as match for objective. You can find out more about this duplex stainless steel riser fitness-for-service work right here.
Another case involving deepwater risers noticed TWI perform a sequence of detailed engineering vital assessments (ECA) on metal catenary risers forward of set up in an oil and fuel area. The risers had been constructed from C-Mn metal with alloy 625 cladding in vital places and there have been quite a lot of pipe geometries as a consequence of completely different service necessities. TWI was requested to find out the utmost preliminary allowable flaw sizes that may make sure the integrity of the risers by means of set up and operation whereas additionally taking account of attainable fatigue loading, bitter service and inside corrosion throughout operation. The structural integrity of the risers is vital, contemplating the excessive strain flammable fluids they’ll comprise and the proximity to the platform which can be manned. They additionally want to have the ability to stand up to quite a lot of hundreds, each static and cyclic, together with inside strain, self-weight, fatigue loading and loading from ocean currents, and to a spread of environmental degradation mechanisms, together with exterior and inside corrosion, and environmentally assisted cracking (significantly in the presence of bitter fluids, i.e. these containing hydrogen sulphide).
TWI examined the structural integrity of the girth welds as they’re topic to cyclic (fatigue) loading and can’t normally be inspected as soon as put in. Careful examination of the standard of supplies, welding and inspection, together with the ECA to look into the connection between flaw measurement, supplies and loading can be sure that flaws won’t develop giant sufficient to result in failure of the riser throughout its design life. These calculations had been carried out utilizing BS 7910, backed up by validation knowledge to evaluate the integrity of the mission. You can find out more about this project to ensure the structural integrity of deepwater risers right here.
TWI is holding a associated Sour Corrosion Training Course – offering data on efficiency and testing supplies in bitter service. The course will present a wonderful introduction for engineers trying to develop their data in this space.
Experts from TWI will even be on the world’s largest corrosion convention and exposition once we attend NACE International’s event in Phoenix, Arizona from 15-19 April, 2018.
You can find out more about TWI’s work with aggressive environment testing right here, or, please contact us for extra data.
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