Materials Selection & Design

MIC Failure of Type 316L Seawater Pipeline

A Type 316L stainless steel (SS) (UNS S31600) pipeline carrying seawater suffered pitting and leakage within a few years of installation. Visual examination revealed penetrations and shallow pits. Electron probe microanalysis results indicated a decrease in chromium concentration within the pit and in the iron concentration at the pit periphery. Microbial investigation confirmed the presence of sulfate-reducing bacteria and chromium-, manganese-, and iron-oxidizing bacteria.

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.

Failure of Glass-Reinforced Epoxy Material Piping Components on an Offshore Platform

Glass-reinforced epoxy (GRE) is a synergistic combination of two or more materials with a reinforcement of E-glass fiber. The brittle nature of the material demands careful handling during transportation, fabrication, and installation. This article describes the analysis of components that failed in a GRE piping system. The failed components were examined through destructive and nondestructive tests. The failure modes and analysis revealed that the combined effect of manufacturing defects and installation practices caused various types of failures.

Failure of Electrolyte Pipelines in a Chlorine and Alkali Factory

The failure of electrolyte pipelines made of 1Cr18Ni9Ti steel in a chlorine and alkali factory was investigated. Corrosion was caused by localized attack from the accumulation of chloric ion and hydrogen induced by welding. The corrosion resistances of two alloys in chlorine and alkali industrial environments were determined. It was suggested that Type 304 stainless steel (SS) (UNS S30400) or Type 316 SS (UNS S31600) be substituted for 1Cr18Ni9Ti steel.

Oil Refining Heater Tube Failures from Internal Melting

The mechanisms that usually limit the life of tubes in oil refining heaters are excessive wall thinning from corrosion, erosion, or creep. Tube selection for this service is usually based on material that will withstand these factors. It is not uncommon, however, to experience tube failures from operational factors. This article describes cases where flow restrictions within tubes led to melting from the inside out.

Erosion-Corrosion Failure of a Spiral Heat Exchanger

This article discusses a failure on a Type 316 stainless steel (UNS S31600) spiral heat exchanger. The failure occurred just five months after the equipment had been put into service. The study showed that degradation occurred from erosion-corrosion in the vicinity of the spacers between the metal sheets.

Using Industrial Computerized Tomography for Corrosion Investigation

Industrial computerized tomography (ICT) was used to investigate the corrosion failure of a chlorine condenser tube, shell, and welding. The ICT analysis indicated that corrosion was most serious where the tube and shell were welded together. This work also showed that ICT can be a valuable tool in corrosion analysis because it can detect gaps or interstices, and quantify their size, shape, and position.

Failure of an Air Inlet Header of a Secondary Reformer

Failures from the overheating of components may occur from short- or long-term exposure. Failures may cause plant shutdown, which in turn will have economic implications. Pipes that carry gases at high operating temperatures are susceptible to this type of failure. The more destructive ruptures occur at pipe metal operating temperatures well above the ASME oxidation limits of the material. This is typically above the eutectic transformation temperature for any selected alloy. This article presents the general aspects of overheating failures and a case study of a recent investigation of an air inlet header failure.

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).

Pipeline Restoration at a Generating Station Using Chemical Grout

A gravity-flow water inlet line had developed many ruptures and cracks, leading to appreciable groundwater inflow. Contaminants brought in by the groundwater increased the cost of treating the water for station use. The problem was solved by injecting chemical grout to the exterior side of the pipe.