Search Results for ASTM A204 Grade A

Welds in two CMo steel catalytic gas-oil desulfurizer reactors cracked under hydrogen pressure-temperature conditions that would not have been predicted by the June 1977 revision of the Nelson Curve for that material. Evidence of severe cracking was found in five weld-joint areas during examination of a naphtha desulfurizer by ultrasonic shear wave techniques. Defect indications were found in longitudinal and circumferential seam welds of the ASTM A204, grade A, steel sheet. The vessel was found to have a type 405 stainless steel liner for corrosion protection that was spot welded to the base metal and all vessel welds were found to be overlaid with type 309 stainless steel. Long longitudinal cracks in the weld metal, as well as transverse cracks were exposed after the weld overlay was ground off. A decarburized region on either side of the crack was revealed by metallurgical examination of a cross section of a longitudinal crack. It was concluded that the damage was caused by a form of hydrogen attack. Installation of a used Cr-Mo steel vessel with a type 347 stainless steel weld overlay was suggested as a corrective action.

A vessel made of ASTM A204, grade C, molybdenum alloy steel and used as a hydrogen reformer was found to have cracked in the weld between the shell and the lower head. Six samples from different sections were investigated. The crack was found to be initiated at the edge of the weld in the coarsegrain portion of the HAZ. The microstructure was found to be severely embrittled and severely gassed in an area around the crack. The microstructure of the metal in the head was revealed to be banded and contained spheroidal carbides. The lower head was established by hardness values and microscopic examination to have been overheated for a sufficiently long time to reduce the tensile strength below the minimum required for the steel. It was interpreted that the wide difference in tensile strength between head and weld metal (including HAZ) formed a metallurgical notch that enhanced the diffusion of hydrogen into the metal in the cracked region. The resultant embrittlement and associated fissuring was established to have caused the failure. The hydrogen was diffused out by wrapping the vessel in asbestos and heating followed by cooling as prescribed by ASME code.

This article discusses the effect of using unsuitable alloys, metallurgical discontinuities, fabrication practices, and stress raisers on the failure of a pressure vessel. It provides information on pressure vessels made of composite materials and their welding practices. The article explains the failure of pressure vessels with emphasis on stress-corrosion cracking, hydrogen embrittlement, brittle and ductile fractures, creep and stress rupture, and fatigue with examples.

This article discusses pressure vessels, piping, and associated pressure-boundary items of the types used in nuclear and conventional power plants, refineries, and chemical-processing plants. It begins by explaining the necessity of conducting a failure analysis, followed by the objectives of a failure analysis. Then, the article discusses the processes involved in failure analysis, including codes and standards. Next, fabrication flaws that can develop into failures of in-service pressure vessels and piping are covered. This is followed by sections discussing in-service mechanical and metallurgical failures, environment-assisted cracking failures, and other damage mechanisms that induce cracking failures. Finally, the article provides information on inspection practices.