NIST Warns of Pressure Vessel Weld Problems
Jun 7, 2001 12:00 PM, Mary Davis
A new paper from the National Institute of Standards and Technology (NIST) suggests that more attention must be paid to weld repairs in order to avoid failures due to problems such as stress-corrosion cracking. Difficulties could occur during repair welding of high-strength steel used to manufacture pressure vessels for the storage and transport of liquefied gases.
Even at the outset, a welded joint has a higher risk of failure from degradation of base material near the weld because of the welding 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 prepared by Ivan Samardzic, a visiting scientist from Croatia, and Thomas Siewert of NIST.
The crux of these problems, they report, 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.
More information can be found at NIST