Limit State Design in DNV96 Rules for Submarine Pipeline Systems: Background and Project Experience

Abstract

This paper-prepsred for presentdon at me 1998 W h o m TechmlogyCcnf8reme held in Houston. Texas. 4-7 May 1888. This paper wpr Mlecdsd for pmwnMmn by the OTC Pmgram Gmmdh tdrming wiew of inhmtion H n e d in an abcbsd wbmitbd by he auma[s). Cotltank of lb Pper, as presenW, hsvenatbesnmviewd bytheUf6horeTechndcgyConferencsmdam wkqcctto colr&tion by the -6). The mstsrisl, 06 prssentbd, doe6 not nnarsrily rslbct my pc&on ci the Oflshot-a Techndcgy Conlwsnm or its o f b m . Ebcbonic repmdudon, diibulion, or s b m p ci any part ci lhis p a p for conmsrdsl purposes he willen cmsmtci the 0l)ehore Technology confenma, is prohibibsd. R y h i i to reproduce in print isrssbidsdtosnsbsbPctcinotmws~n 33Jwu-d~; I-m~ynatbecopled.The ak3bact m s t c m t a i n a m s p i a r x r s~r n e n t c i~a n d by *hanthe paperpresentsd. AbstractThis paper discuss the safety philosophy and limit state design methodology adopted in the new revision of Det Norske Veritas @NV) "Rules for Submarine Pipeline Systems".The new Ruies completed late 19% (denoted D W % in the following) constitutes a complete revision of the previous Ruies h m 1981 and provide a significant step fornard for pipeline design and operation. D W % adopts the latest research achievements and practical experience gained through the most challenging pipeline projects recently executed. The adopted limit state format allows for a large flexibility in design. It applies explicit design checks for physical limit states rather than implicit design check covering a number of failure modes.The safety philosophy adopted including the novel safety class concept will be discussed. The background for design criteria related to pressure containment are presented and the principles for assessing and accounting for the influence of system effects, material quality, hydro test and pressure safety systems are discussed.The implicit higher allowable utilisation given by the LRFD-format for the pressure containment is illustrated. Design performance, feedback from the industry and experience gained since the issue will be discussed.

Investigation of Hydrogen Embrittlement Susceptibility and Fracture Toughness Drop after in situ Hydrogen Cathodic Charging for an X65 Pipeline Steel

“…The first relates to the development of elevated internal pressures due to hydrogen adsorption on the micro-cavities of the microstructure, the second to the local increase of the microplasticity resulting in the excess of yield point and the third to the reduction of the interconnectivity between grain boundaries and boundaries of different phases and microstructural components [15][16][17][18][19][20][21].…”

“…Finally, fracture toughness and microhardness values can be successfully correlated with the hydrogen cations' concentration factor in microstructural sites. The fracture toughness of steel decreases with an increase of hydrogen concentration factor, regardless the type of the existing embrittlement mechanism [17][18][19][20][21]24].…”