Research Of Ground Test Procedure And Hydrostatic Test Machine For Subsea Wellhead System

The subsea wellhead is normally run from a floating drilling rig and is located at the mudline. It supports the casing strings and seals off the annuli between them. It is used inconjuction with a subsea BOP stack which locks and seals to the high pressure wellheadhousing. The subsea tree locks and seals to the high pressure housing after drilling iscompleted.To ensure reliable and safety, carrying out a rigorous, comprehensive performance testbefore the subsea wellhead system put into used, is extremely important and necessary. Thisarticle has a research on details of the whole system, referring to API Spec 17D, analyses theworking environment and features of all components, for material, strength, bearing capacityof the different requirements, etc. The main object is to construct a set of reasonable, safetytesting procedures and acceptance criteria.The high pressure wellhead bears the most complicated forces and undergoes variouscomplex loading. During the drilling process at any time, no failure is allowed. Hydrostatictest shall be carried out to verify the pressure integrity of wellhead pressure boundary beforeshipped from factory. A hydrostatic test machine is used in testing the pressure integrity of ahigh pressure wellhead. The most important technology of the hydrostatic test is the sealingmethod, the moving way of sealing end. There are two different kinds of test machine, thevertical and the horizontal. Comparing with the two designs, it concludes the finalconstruction of hydrostatic test machine used for high pressure wellhead.To verify the reliability of the high pressure wellhead design, there is a research on thestress distribution under hydrostatic test, an axial symmetry of subsea high pressure wellheadmodel was established. The simplified finite element model was analyzed, simulating the hydrostatic test condition, with radial sealing style. Result shows that the stress distributionunder hydrostatic test is essentially the same as it is in real working condition, and strengthmeets the qualification. The new style wellhead design is safe and reliable. Finite elementanalysis is proved to be a proposal to the design of subsea wellhead system, including ananalysis of deformation of casing hanger.