Authors: Saher Shawki
Publish Date: 2013/07/25
Volume: 13, Issue: 5, Pages: 595-600
Abstract
The repeated failure of high pressure screw pumps operating in a petroleum oil field required serious attention Two pumps out of three suffered catastrophic failure after relatively short times 6 and 9 months of operation The failure was manifested in both cases by a circular crack in the driven shaft that developed to complete fracture Comprehensive failure analysis of one of the pumps showed that the shaft cracked due to fatigue as a result of the rotary bending process caused by misalignment In addition to the faulty operation and inaccurate maintenance the material of construction martensitic stainless steel 420 in the asbuilt condition was considered to be a major cause of damage Type 420 attains maximum corrosion resistance increased strength and hardness when it is fully hardened However a stress relief operation should follow the hardening treatment as toughness tends to decrease with increasing hardness to oppose fatigue cracking
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