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Materials and properties

Explosive decompression

Explosive decompression damage isstructural failure in the forms of blistering, internal cracking and splits caused when the gas pressure, to which the seal is exposed, is rapidly reduced from high to low. Inorder to overcome many of the problems associated with high pressure gas systems, we have conductedintensive materials developmentprogrammes over the last 20 years. Much of this work was carried out in collaboration with equipment manufacturers, major oil and gasoperators, and research bodies.We offer five standard grades of EDresistant elastomer, all of which have been extensively validated in-house.They aretested, approved and specified by oilfieldoperators and equipment manufacturers alike. Although explosive decompression (ED) is aphenomenon generally found in the oil and gas industry, it can be experienced in any application where there is a rapid drop in gas pressure. ED damage has been noted in sealingapplications ranging from paint guns and fire extinguishers to marine stern gland seals and systems containing refrigerants. The elastomeric components of a system are, to a greater or lesser extent, susceptible to the permeation and diffusion of gasesdissolving in their surface. With time, thesecomponents will become saturated with whatever gases are in the system. Under these conditions – as long as the internal gas pressure of the elastomer remains at equilibrium with the ambientpressure – there is minimal damage, if any,and no deterioration in performance of the elastomeric component occurs (unless caused by other factors such as chemical or thermal degradation or by extrusiondamage). The formulation, mixing, quality control and processing of these compounds is rigorously controlled and today they arerated by many as the benchmarks by whichall others are judged. Although each ofthese compounds has a broad range of application capability, their particularfeatures are as follows: When the external gas pressure is removedor pressure fluctuations occur, large pressure gradients are created between theinterior and the surface of the elastomericcomponent. This pressure differential may be balanced by the gas simply diffusing/ permeating out of the elastomer, especially if any external constraints are not removed.
â—� FR58/90 –Afluoroelastomer (FKM) withexcellent chemical and thermal properties, plus ED resistance inhydrocarbon applications. It is approvedand specified by many oil producers and equipment manufacturers. However, if the physical properties of the elastomeric compound cannot resist crack and blister growth during thepermeation process, then structural failureis the inevitable result.Explosive decompression damage canmanifest itself in various ways – anythingfrom internal splits that are not visible onthe surface of the seal to surface blisters, fractures and complete fragmentation.
â—� FR25/90 –This fluoroelastomer (FKM)combines an improved low temperature capability with excellent thermal andchemical properties. It is ED resistant inhydrocarbon applications.
â—� Elast-O-Lion 101 – An hydrogenatednitrile (HNBR) grade with high mechanical strength and wear resistantproperties. It has good resistance tomany oilfield chemicals including H
‘O’ rings after explosive decompression. 2 Sand amine corrosion inhibitors. It is resistant to explosive decompressionand is approved to many EDspecifications.
James Walker’s eight-flange explosive decompression test rigs. â—� Elast-O-Lion 985 – This hydrogenatednitrile (HNBR) grade offers improved low temperature capacity, but with reducedmechanical properties and ED resistancecompared to Elast-O-Lion 101.
â—� AF69/90 –An Aflas
® (TFE/P) based EDresistant grade with excellent resistance to oilfield media and steam. To order or get further details, call your local contact shown on rear cover or listed at www.jameswalker.biz 9