NDLI: A Fatigue Failure Mechanism of Welded Piping Joints

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Hassan, Tasnim Lu, Xiangyang
Copyright Year	2005
Abstract	Fatigue failures of small bore piping systems have historically occurred in nuclear power plants, resulting in unanticipated plant downtime and substantial financial loss. If the failures were not caused by defects, the reasons of the initiation of fatigue cracks were not clear in many cases. This paper presented a set of weld fatigue response data which pointed to the strain ratcheting response as a probable reason for weld fatigue failure. A systematic set of low-cycle fatigue tests on butt- and socket welded piping joints in the cantilever set up is conducted. A new observation made in these tests is that the recorded strains near the weld toe ratchet continuously, which results in the initiation of fatigue crack(s). Comparison of these ratcheting responses with those from the cyclic bending of straight pipe and ratcheting experiments at the material level indicates that the residual stresses at welded joints may induce the ratcheting responses. This observation is further supported by the symmetric strain response (no ratcheting) at the mid-pipe length, which is located away from the welded joint. At this location, there are no residual stresses to induce ratcheting. It is observed that the fatigue cracks in all experiments occurred at the weld toe location where the ratcheting strain is the largest. The experimental data indicate that the fatigue life of materials is reduced in the presence of ratcheting. It is also observed that the ratcheting is influenced by the welding sequence. One interesting aspect of the weld fatigue data developed is that the ratcheting at the weld joints occurred under a displacement-controlled loading cycle. This study with its limited time and resource could not explore this issue. A plausible reason could be due to material heterogeneity at the welded joints.
Sponsorship	Pressure Vessels and Piping Division
Starting Page	119
Ending Page	125
Page Count	7
File Format	PDF
ISBN	079184188X
DOI	10.1115/PVP2005-71269
e-ISBN	0791837637
Volume Number	Volume 3: Design and Analysis
Conference Proceedings	ASME 2005 Pressure Vessels and Piping Conference
Language	English
Publisher Date	2005-07-17
Publisher Place	Denver, Colorado, USA
Access Restriction	Subscribed
Subject Keyword	Cycles Fatigue life Welding Fatigue Fatigue failure Residual stresses Pipe joints Displacement Low cycle fatigue Piping systems Cantilevers Welded joints Downtime Nuclear power stations Pipes Fatigue cracks Failure
Content Type	Text
Resource Type	Article

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