NIST SAYS "MORE ATTENTION MUST BE PAID TO REPAIR WELDS".A new paper from NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. suggests that more attention must be paid to weld repairs in order to avoid failures due to problems such as stress-corrosion cracking cracking - cracker . Even at the outset, a welded joint Welded joint The joining of two or more metallic components by introducing fused metal (welding rod) into a fillet between the components or by raising the temperature of their surfaces or edges to the fusion temperature and applying pressure (flash welding). has a higher risk of failure from degradation of base material near the weld because of the welding welding, process for joining separate pieces of metal in a continuous metallic bond. Cold-pressure welding is accomplished by the application of high pressure at room temperature; forge welding (forging) is done by means of hammering, with the addition of heat. process itself. This risk of failure is increased if repair welding is performed. "Therefore, the welding, quality control and quality assurance technologies need to be developed to more stringent requirements if we want to avoid the conditions for failure, and so achieve higher reliability for welded construction," reads the report. The paper discusses possible difficulties that could occur during repair welding of high-strength steel used to manufacture pressure vessels Pressure vessel A cylindrical or spherical metal container capable of withstanding pressures exerted by the material enclosed. Pressure vessels are important because many liquids and gases must be stored under high pressure. for the storage and transport of liquefied gases. The crux Crux (kr  ks) [Lat.,=cross], small but brilliant southern constellation whose four most prominent members form a Latin cross, the famous Southern Cross. of these problems is
the complex temperature variations that occur during the welding repair
which "can cause significant degradation of the welded-joint
zone."
Repair welds are usually short, so their temperature fields are more complex than long welds. The degradation is most severe at weld starts and stops, but also can occur at other locations along the weld and for different stress conditions. Much of the report concerns degradation in properties at the weld starts and stops. For a copy of paper No. 18-01, contact Sarabeth Harris, NIST, MC1O4, Boulder, CO 80305-3328; (303) 497-3237; sarabeth@boulder.nist.gov. |
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