Failure Analyses

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.

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.

Formicary Corrosion of Cupronickel Tubing

The occurrence of formicary corrosion, or ant-nest corrosion, has been primarily reported throughout the heating, ventilation, and air-conditioning industry. Until now, the presence of formicary corrosion has been limited to refrigeration-grade copper (99.99% Cu). A failure investigation has attributed leaks in cupronickel tubing to formicary corrosion.

Rapid Failure of a Copper/Nickel Overhead Condenser Bundle

Rapid and unexpected failure of a CuNi bundle of a stabilizer overhead condenser occurred where an Al-brass bundle showed chemical resistance for more than 20 years. An investigation revealed that the intergranular attack/cracking of the cupronickel tubes was caused by attack of a wet hydrogen sulfide (H2S)- containing medium. Literature indicated that cupronickel is much more susceptible to attack by wet H2S than Al-brass. Cupronickel is unsuitable as tube material in overhead systems containing significant amounts of H2Sand ammonia (NH3).