Causes´ Analysis of Cracks During Welding of High-Pressure Vessel Body Made of Titanium Alloy

Abstract

Purpose of reseach is to identify the causes of cracks during welding of high-pressure vessel body made of titanium alloy.Methods. Features of welded joint microstructure of high-pressure vessel body made of titanium alloy are described and studied by color flaw detection methods, fluoroscopy, and examination of the cuts. The causes of cracks in the bodies of pressure vessels are identified. The causes are a combination of internal stresses and structures features.Results. Based on the analysis of cut samples microstructure, it follows that the stamping of the power element was supplied without preliminary heat treatment. The formation of crack foci on the inner surface of the power element, at the place of alloy transition to the area of the attachment site, is primarily associated with large volumetric internal stresses, which are additionally summed up with surface stresses from machining and thermal stresses during welding. Based on the obtained data, it follows that when using a specialized tooling with a copper backing that provides pressurization of inert gas, welding stresses in a weld area are reduced by several orders of magnitude compared to the area where the tooling was without copper backing. As a result of the study, it was revealed that the causes of cracks in the bodies of high-pressure vessels are a combination of internal stresses due to the lack of preliminary thermal treatment of power elements made of titanium alloy, which are part of a high-pressure vessel, as well as stresses arising during welding of the power element with shells, considering design features.Conclusion. To eliminate the cause of cracks, additional experimental work was carried out. Surfacing the manual ADF of reinforcing roller into the zone of maximum stresses of the power element was done. The proposed solution met expectations - all the bodies of high-pressure vessels passed hydraulic tests, which made it possible to preserve material part.