AWS WHC-4.09:2010

Maintenance and Repair Welding
Scope : Maintenance and repair welding began when early man heated a broken tool in a charcoal fire and hammered the metal pieces into one shape. Forge welding was developed from this early process. By the 16th century, some welding repairs were made by fusion processes. These early repair techniques were inexact, and success of the repair was never certain. After centuries of accumulated technology and improvements to processes and methods, the quality and reliability of modern welded repairs equal the high standards of new construction. Efficient methods of analyzing metal alloys and a deeper understanding of metal fatigue, fracture mechanics, and metallurgical properties have contributed to this quality. For example, portable alloy analysis equipment and metallographic and other testing equipment can be used to determine actual metal properties while the component is in service without affecting the integrity of the component. Mechanical tests are available to assess changes in metal bending and tensile properties, toughness, and metallurgical grain structures. Nondestructive tests provide accurate surface and subsurface flaw detection and defect sizing. The economic advantages of avoiding business interruptions, extending equipment life, and saving the time required to build replacement components justifies the use of advanced forensic metal examination techniques. In some cases, however, repair welding may require the selection of welding parameters based on experience and knowledge, without the benefit of confirming the original joint design, material grade, initial welding process, heat treatment, or quality standards of the item. In addition, repair welding techniques often are complicated by difficult situational factors; for example, welding facilities may not be prepared to perform specific maintenance and repair welds. A systematic approach to maintenance and repair welding is presented in this chapter, based on a decision model for analysis of the required repairs and a checklist designed to ensure that all the variables associated with the specific welding operation will be considered. The checklist template addresses the cause of the failure, the need for repair, and whether the machine or component can be repaired safely and efficiently. The checklist will help determine if component repair or replacement is the correct action. Other considerations are code requirements or regulations that govern the repair welding of the item.1 It should be noted that the principles of maintenance and repair by welding also can be applied to other materials-joining processes, such as brazing, soldering and allied processes.2 This chapter contains information that will help to produce technically sound cost-efficient welded repairs. Several case histories of successful maintenance and repair welding are described in the Applications section of this chapter.