Sulfide Stress Corrosion Cracking in Welded Joints of Welded Linepipes.

Abstract

The sulfide stress cracking (SSC) behavior of welded linepipes has been studied using some SSC tests, such as tensile SSCtest (NACE-TM 0177-90 Method A), full thickness SSCtests, four points bending SSCtests and full scale SSCtests. Detailed metallographic examinations have been performed in order to undeTstand the influences of steel chemistries and heat inputs in welding on the SSC resistance of the heat affected zone. The effects of the geometry of the SSC specimen and hydrogen concentration on the SSC have also been investigated. The resu[ts have indicated that homogenized bainitic ferrite microstructure, which can be attained by reducing carbon content and by applying accelerated cooling after controlled rolling in plate rolling process, improves the resistance of steel plates to the SSC.Meanwhile, most specimens from submergedarc welding welded joints fai] at the heat affected zone, regardless of differences in the rr'icrostructures of base materials, and they tend to show nearly the same level of the ratio of threshold stress to yield strength in the tensile SSC tests. Specimengeometry and the quantity of hydrogen con- centration in stee[ affect on the threshold stress, and hence reducing the hydrogen concentration improves the SSC resistance of the welded joints especially in lower hardness heat affected zone. Relations between the resu[ts of the laboratory tests and full scale tests are also discussed.