Ramifications Of Cracks At The Fillet Welds Of High Temperature Steam Headers

摘要

During a major statutory inspection of a 150MW steam raising boiler, cracks were found at the stub tube-to-header fillet weld of both the secondary superheater outlet header and the reheater outlet header. These cracks extended in some instances up to halfway through the tube wall thickness. The extent of the cracking precluded immediate and widespread repair and so an engineering solution was devised to identify the most critical cracks and repair these while leaving less critically cracked stubs in service. While the unit was returned to service, the long-term life of the boiler was in question. The expected life of these headers was compared with the required life of the unit and the economic issues of repairing stubs compared to replacing with a new header and stubs, the result being a new for old replacement. This paper will describe the extent of the cracking found, the engineering calculations undertaken to ensure the safe return of these headers to service and the longer-term life issues.