Materials Selection & Design

A Closer Look at Microbiologically Influenced Corrosion

Microbiologically influenced corrosion (MIC) refers to corrosion caused by the presence and activities of microorganisms—microalgae, bacteria, and fungi. While microorganisms do not produce unique types of corrosion, they can accelerate corrosion reactions or shift corrosion mechanisms. Microbial action has been identified as a contributor to rapid corrosion of metals and alloys exposed to soils; seawater, distilled water, and freshwater; crude oil, hydrocarbon fuels, and process chemicals; and sewage. Many industries and infrastructure are affected by MIC, including oil production, power generation, transportation, and water and waste water.

The Fine Art of Predicting Failures Just Before They Occur

When predicting a corrosion failure, ideally the time frame should be of sufficient duration to enable operators to take the appropriate action and eliminate the hazard. Occasionally it happens that a potential failure is predicted just before it actually occurs. This article describes such a situation.

Corrosion of Old Whaling Station Processing Equipment in Antarctica

The author visited Antarctica in January 2006. He came across several metal artifacts that had been there since early in the 20th century. Corrosion is not a serious problem in Antarctica’s environment, as evidenced by the relatively good condition of the artifacts.

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.

Failure Analysis of Pyrolysis Furnace Transfer Line Tubes

Transfer line tubes of an ethane pyrolysis furnace, operating at 850 ±20 °C and 1.0 atm pressure, developed longitudinal cracks after less than one third of their expected service life. The tubes were constructed of Fe-based UNS N08810 alloy with a wall thickness of 10 mm. Metallurgical evaluation revealed that the mode of failure was high-temperature carburization attack leading to intergranular cracking. The cause of failure was overheating, likely to have occurred during decoking operations. Better control of furnace temperature was recommended to avoid overheating. Alternatively, a wrought alloy capable of developing highly protective aluminum oxide (Al2O3)-base scale such as Ni-based UNS N07214 could be used as a replacement.

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.

Unusual Occurrence Causes Leak in High-Pressure Underground Gas Pipeline

A gas leak was detected on a 56-in (1.4-m) crosscountry gas pipeline from a small orifice on the bottom of an indentation. The pipeline had an epoxy primer and a hot polyethylene coating, and was only four years old. Metallurgical tests on the hole and theoretical calculations indicated that the pipeline had been penetrated by a bullet before being coated. This may be the first such case recorded, and would have been difficult to prove if an explosion had taken place.

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.

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.