Common root causes of recent failures of flanges in pressure vessels subjected to dynamic loads

Authors
Otegui, Luis Jose; Fazzini, Pablo Gabriel; Marquez, Anibal Angel
Publication Year
2008
Language
English
Format
article
Status
Published version
Description
Present rules in fabrication codes are aimed to reduce the probability of fatigue cracks in flanges welded to pressure vessels subjected to cyclic pressure or vibrations. Yet, several leaks and ruptures have recently occurred at flanges in pressure vessels and pipes. A review of three cases is presented, which involved five failures; their common root causes are discussed, and the influences of manufacture and operation conditions on crack initiation and propagation mechanisms are highlighted. Some cracks initiate from the outer surface, but many cracks initiate in the outer half of the thickness of the reinforcement, from very difficult to avoid weld defects. Ultrasonic testing, with an adequate procedure, can be reliably used to detect these defects before they become leaks. Common aspects of these failures are crack initiation in weld metal and heat affected zone of welds, all related to an inadequate design of the reinforcement and poor execution of the welding procedure. Weld inadequacy is in one case a result of an increase in thickness as an attempt to increase safety; which also increased cyclic stresses due to excessive weight of the vessel. Fillet welded reinforcements induced rigidity inconsistencies within the flange joint, and concentrated deformations in the failed regions. In another case, preoperational hydrotest could have been detrimental.
Fil: Otegui, Luis Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina
Fil: Fazzini, Pablo Gabriel. GIE S.A.; Argentina
Fil: Marquez, Anibal Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina
Subject
In service failures
Fatigue failures
Pressure vessels
Flanges
Reinforcement saddles
Weld defects
Recubrimientos y Películas
Ingeniería de los Materiales
INGENIERÍAS Y TECNOLOGÍAS
Access level
Restricted access
License
https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
Repository
CONICET Digital (CONICET)
Institution
Consejo Nacional de Investigaciones Científicas y Técnicas
OAI Identifier
oai:ri.conicet.gov.ar:11336/66256