INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
artículos
Título:
Common root causes of recent failures of flanges in pressure vessels subjected to dynamic loads
Autor/es:
J.L. OTEGUI; P.G. FAZZINI; A. MARQUEZ
Revista:
Engineering Failure Analysis
Editorial:
ELSEVIER
Referencias:
Año: 2009 vol. 16 p. 1825 - 1836
ISSN:
1350-6307
Resumen:
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.