SULFIDE STRESS-CORROSION CRACKING IN WELDED-JOINTS OF WELDED LINEPIPES

The sulfide stress cracking (SSC) behavior of welded linepipes has bee n studied using some SSC tests, such as tensile SSC test (NACE-TM 01 7 7-90 Method A), full thickness SSC tests, four points bending SSC test s and full scale SSC tests. Detailed metallographic examinations have been performed in order to understand the influences of steel chemistr ies and heat inputs in welding on the SSC resistance of the heat affec ted zone. The effects of the geometry of the SSC specimen and hydrogen concentration on the SSC have also been investigated. The results hav e indicated that homogenized bainitic ferrite microstructure, which ca n be attained by reducing carbon content and by applying accelerated c ooling after controlled rolling in plate rolling process, improves the resistance of steel plates to the SSC. Meanwhile, most specimens from submerged arc welding welded joints fail at the heat affected zone, r egardless of differences in the microstructures of base materials, and they tend to show nearly the same level of the ratio of threshold str ess to yield strength in the tensile SSC tests. Specimen geometry and the quantity of hydrogen concentration in steel affect on the threshol d stress, and hence reducing the hydrogen concentration improves the S SC resistance of the welded joints especially in lower hardness heat a ffected zone. Relations between the results of the laboratory tests an d full scale tests are also discussed.