The weldability of steels used in jack-up drilling platforms

Abstract

Weldability problems in jack-up rigs arise principally in leg construction where particularly high-strength steels (∼690 N mm −2 yield) are used for chords and racks. Attainment of mechanical properties is not usually difficult, although procedural trials are advisable. Of potential fabrication problems, hydrogen cracking (heat-affected zones or weld metal) is of greatest concern, and consideration of solidification cracking is advisable. Lamellar tearing is not generally a problem with modern steels, and the risk of stress-relief cracking will be confined to the limited number of joints which can be heat-treated. Fatigue cracking is probably the major cause of service failure of jack-up rigs, and the use of high-strength steels, which permits higher static stress limits, can exacerbate this problem. Hydrogen-induced stress corrosion can also occur, either due to cathodic polarisation or corrosion, particularly in the presence of H 2S in foul sea-water. For this reason weld hardness limits need to be maintained.