Failure Analyses

SCC Failure of a Super Duplex Separator Vessel in an Ammonium Nitrate Plant

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.

Role of Surface Finish in Fatigue Failure of Type 316L Stainless Steel Coil Tube

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.

Failure of a Column Reboiler in a MEG Recovery Unit

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.

Stress Corrosion Cracking of a Vinyl Chloride Stripper Vessel

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.

Failure Analysis, Part II—Case Histories

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.

Stress Cracking of Stainless Steel Safety Gate Valve Stem

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.

Short-Term Overheating of Baffle Boiler Tubes

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.

Premium Connection Downhole Tubing Corrosion

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.