This article presents findings of a failure investigation on a separator vessel in an ammonium nitrate (NH4NO3) plant. The super duplex stainless steel vessel leaked due to stress corrosion cracking initiated in the heat-affected zones of welds exposed to the NH4NO3 solution at ~180 °C.
A Type 316L stainless steel (UNS S31603) coil
tube used for dehydration of wet gas with
tri-ethylene glycol cracked and failed after less than
one year of service in a platform gas processing
facility. The investigation revealed multiple fatigue
cracks at a plastically deformed area on the coil
external surface. Vibration of the coil tube during
service caused the cracking.
After only seven months of operation, a column
reboiler in a mono-ethylene glycol recycling unit at
a natural gas production plant failed because of
localized corrosion on the portion of the tubes in the
tube sheet. This attack was caused by abnormal
clearance between the tubes and tube sheet, due to
poor manufacturing quality, which allowed
deposits to collect and initiate crevice corrosion.
This article describes the findings of a detailed
failure investigation on a UNS S32750 super
duplex stainless steel vinyl chloride stripper vessel
that experienced cracking at nearly half of the
welds. The cracking was identified as Type A
“active-passive” stress corrosion cracking, which
initiated on the inside of the vessel at both the
circumferential and longitudinal welds.
The academic side of failure analysis was presented
in Part I of this article. This included 1) steps in conducting a failure analysis, 2) typical tools, and 3) theory of crack propagation. This article provides several case studies demonstrating the use of these techniques.
This study investigated the failure of a 15-5 PH
(UNS S15500) precipitation-hardened stainless
steel stem when installed in a 5 1/8-in (130-mm)
hydraulic surface safety gate valve working in a sour
gas environment. The results indicate that the
fracture failure was caused by sulfide stress
cracking, which progressed transgranularly
in the martensitic matrix.
Several tubes in a baffle boiler experienced bending
and one tube failed. Tests showed appreciable
changes in hardness and microstructure on the
failed tube. Failure occurred because of short-term
overheating of the tube.
This article discusses a field background search,
macro- and micro-corrosion morphology analysis,
and material testing of corroded premium
connection downhole tubing. Tubing failure was
caused by erosion-corrosion from highly disturbed
liquid and high shear stress at the couplings.