Residual strength of dented pipelines, DNC test results

Pipel ines can be exposed to ex te rna l in te r fe rence resul t ing in d a m a g e in the form of dents , c racks and notches. Such d a m a g e may reduce the capaci ty of the pipeline, and for f u r t h e r safe opera t ion of the pipel ine a rel iable eva lua t ion of the defects a re of impor tance . At p resen t several assessment methods a re avai lable , bu t there is a need to eva lua te these methods aga ins t test results. DNV per fo rmed 14 tests on den ted pipes between 1979-1981, sponsored by several oil and gas companies . The tests included pure dents , the combina t ion of den t and notch, and also the effect of r epa i r of the notch by gr ind ing . This pape r presents those test results. The test resul ts a re used in a J I P pro jec t with the object ive to develop a Defect Assessment M a n u a l for pipelines, conduc ted by A n d r e w P a l m e r & Associates, D N V and several o the r organisa t ions , (Cosham, Ki rkwood, 2000) D N V f inds it beneficial for the indus t ry as a whole t h a t the results ob ta ined f rom the tests a re publ i shed and made avai lable , and has the re fo r decided to publ ish the b a c k g r o u n d in format ion and t he tes t results . I N T R O D U C T I O N Damage in the form of dents, cracks and notches can significantly reduce the pressure containment capacity of a pipe. in order to be able to develop and validate potential future capacity criteria test data is of importance. By presenting the test results the industry can compare and validate the various criterion against these results. A total of 14 full-scale burst tests with pipes containing pure dents, dents and notch, and the notch ground were carried out. The tests were conducted as a Joint Industry Project to investigate the residual strength of damaged pipelines and risers. Large diameter pipelines were used in the tests, where 9 of the tests were carried out on 814ram (32") diameter pipes and 5 on 273mm (10") diameter pipes. Extensive material tests of the tested pipes were also carried out. O V E R V I E W O F TEST AND R E S U L T S An overview of the tests and the test results are given in table 1, while more detailed information of the tests are given in the following.