Weld repairs to high-pressure feed/effluent heat exchangers

摘要

Two feed/effluent heat exchangers in a Hydrocracker Unit had suffered from hot sulphur corrosion and a weld repair became necessary to avoid potential collapse of the internal gasket seating face and the subsequent ingress of high-pressure hydrogen into a low-pressure region. The repair technique involved site machining followed by weld build up using the semi-automatic pulsed gas metal arc welding process with an AISI 309LSi type of consumable. The parent material was 2.25 Cr. 1 Mo with a thickness of 300 mm, and the problems associated with welding operators having to enter a vessel of 1200 mm internal diameter at a preheat of 200℃ are described. The difficulties associated with post weld heat treatment are also described, as well as the non-destructive testing limitations. Repairs were carried out in a satisfactory manner to exchangers in 1995 and again in 1997.