A 25.4 cm (10 in.) diam gray cast iron water main pipe was buried in the soil beneath a concrete slab. The installation was believed to have been completed in the early 20th century. A leak from the pipe resulted in flooding of a warehouse. Once removed, the pipe revealed through-wall perforations and cracking along its axis. The perforations and the crack were at the 6 o'clock position. Investigation (visual inspection, radiography, unetched macrographs, and tensile testing) supported the conclusion that the failure occurred as result of years of exposure to ground water in the soil resulting in graphitic corrosion. Soils containing sulfates are particularly aggressive. Recommendations included pipe replacement. The wall thickness had been sufficiently reduced that the pipe could no longer support the required load. Water mains are designed for more than 100 years life. Ductile iron or coated and lined steel pipe, generally not susceptible to graphitic corrosion, were suggested as suitable replacement materials, and cathodic protection was also considered as a possibility.

One of five underground drain lines intended to carry a highly acidic effluent from a chemical-processing plant to distant holding tanks failed in just a few months. Each line was made of 304L stainless steel pipe 73 mm (2 in.) in diam with a 5 mm (0.203 in.) wall thickness. Lengths of pipe were joined by shielded metal arc welding. Soundness of the welded joints was determined by water back-pressure testing after several lengths of pipe had been installed and joined. Before completion of the pipeline, a pressure drop was observed during back-pressure testing. An extreme depression in the backfill revealed the site of failure. Analysis (visual inspection, electrical conductivity, and soil analysis) supported the conclusions that the failure had resulted from galvanic corrosion at a point where the corrosivity of the soil was substantially greater than the average, resulting in a voltage decrease near the point of failure of about 1.3 to 1.7 V. Recommendations included that the pipelines be asphalt coated and enclosed in a concrete trough with a concrete cover. Also, magnesium anodes, connected electrically to each line, should be installed at periodic intervals along their entire length to provide cathodic protection.

A failure of an aboveground storage tank occurred due to external corrosion of the tank floor. The liquid asphalt tank operated at elevated temperatures (approximately 177 deg C, or 350 deg F) and had been in service for six years. Cathodic protection (rectifiers) had been installed since start-up of the tank operation. It was noted, however, that some operational problems with the rectifier may have interrupted its protection. Investigation (visual inspection, on-site examination and testing, EDS analysis of scale deposits, and MIC testing of the soil) supported the conclusion that corrosion may have been caused by an interruption in cathodic protection. The effectiveness of cathodic protection on established microbial deposits is questionable. Recommendations included ultrasonically testing the tank floor and replacing portions based on the remaining wall thickness. Doubling the wall thickness of the floor plates was also recommended.

This paper describes the investigation of a corrosion failure of bottom plates on an aboveground tank used for the storage of potable water. The tank was internally inspected for the first time after six years of service. Paint blisters and rust spots were observed on the bottom plates and first to third course shell plates. Sand blasting and repainting of the bottom plates and first course shell plates was to be used as a remedial measure. However, during the sand blasting, holes and deep pitting were observed on the bottom plates. On-site visual inspection, magnetic flux leakage (MFL) inspection, ultrasonic testing (UT), and evaluation of the external cathodic protection (CP) system were used in the failure analysis. The corrosion products were analyzed using energy-dispersive X-ray analysis (EDAX). The failure is attributed to the ingress of water and its impoundment under the tank bottom along the periphery inside the ring wall and failure of water side epoxy coating. Various measures to prevent such failures in the future are recommended.

Corrosion in potable and nonpotable water systems has been well documented in the past, and new research discusses innovations in water treatment and materials that are designed to enhance the quality of a water system, whether commercial or residential. This paper is a collection of five case histories on the failure of copper and steels as used in potable and non-potable water systems. The case histories cover a range of applications in which copper and steel products have been used. Copper and steel pipes are the two most commonly used materials in residential, commercial and industrial applications. The projects that are discussed cover these three important applications. The purpose of presenting this information is to allow the reader to gain an understanding of real life corrosion issues that affect plumbing materials, how they should have been addressed during the design of the water system, and how a water system should be maintained during service. We share this information in the hope that the reader will gain some limited knowledge of the problems that exist, and apply that knowledge in designing or using water systems in day-to day life.

This article focuses on the mechanisms of microbially induced or influenced corrosion (MIC) of metallic materials as an introduction to the recognition, management, and prevention of microbiological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It discusses the degradation of various protective systems, such as corrosion inhibitors and lubricants. The article describes the failure analysis of steel, iron, copper, aluminum, and their alloys. It also discusses the probes available to monitor conditions relevant to MIC in industrial systems and the sampling and analysis of conditions usually achieved by the installation of removable coupons in the target system. The article also explains the prevention and control strategies of MIC in industrial systems.

This study examines the role of calcium-precipitating bacteria (CPB) in heat exchanger tube failures. Several types of bacteria, including Serratia sp. (FJ973548), Enterobacter sp. (FJ973549, FJ973550), and Enterococcus sp. (FJ973551), were found in scale collected from heat exchanger tubes taken out of service at a gas turbine power station. The corrosive effect of each type of bacteria on mild steel was investigated using electrochemical (polarization and impedance) techniques, and the biogenic calcium scale formations analyzed by XRD. It was shown that the bacteria contribute directly to the formation of calcium carbonate, a critical factor in the buildup of scale and pitting corrosion on heat exchanger tubes.

This article focuses on the mechanisms of microbiologically influenced corrosion as a basis for discussion on the diagnosis, management, and prevention of biological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It begins with an overview of the scope of microbial activity and the corrosion process. Then, various mechanisms that influence corrosion in microorganisms are discussed. The focus is on the incremental activities needed to assess the role played by microorganisms, if any, in the overall scenario. The article presents a case study that illustrates opportunities to improve operating processes and procedures related to the management of system integrity. Industry experience with corrosion-resistant alloys of steel, copper, and aluminum is reviewed. The article ends with a discussion on monitoring and preventing microbiologically influenced corrosion failures.

Diagnosis of environmentally induced failures is greatly facilitated by metallographic analysis. As an example, a failure analysis of ASTM A574 material grade bolts is presented. The bolts served as bonnet screws in underground valves and failed due to stress-corrosion cracking. Metallographic methods were used to diagnose and provide solutions for the service failure. Included are photos showing crack propagation morphology and fracture surface appearance.

A steam-condensate line (type 316 stainless steel tubing) began leaking after five to six years in service. The line carried steam condensate at 120 deg C (250 deg F) with a two hour heat-up/cool-down cycle. No chemical treatment had been given to either the condensate or the boiler water. To check for chlorides, the inside of the tubing was rinsed with distilled water, and the rinse water was collected in a clean beaker. A few drops of silver nitrate solution were added to the rinse water, which clouded slightly because of the formation of insoluble silver chloride. This and additional investigation (visual inspection, and 250x micrograph etched with aqua regia) supported the conclusion that the tubing failed by chloride SCC. Chlorides in the steam condensate also caused corrosion of the inner surface of the tubing. Stress was produced when the tubing was bent during installation. Recommendations included providing water treatment to remove chlorides from the system. Continuous flow should be maintained throughout the entire tubing system to prevent concentration of chlorides. No chloride-containing water should be permitted to remain in the system during shutdown periods, and bending of tubing during installation should be avoided to reduce residual stress.

After operating for six months, a pump impeller (of nickel-containing cast iron) showed considerable corrosion. Cross sections showed substantial penetration of the wall thickness without loss of material. The observed supercooled structure implied low strength but would not affect corrosion resistance. Etching of the core structure showed a selective form of cast iron corrosion (spongiosis or graphitic corrosion) which lowered the strength of the cast iron enough that a knife could scrape off a black powder (10.85% C, 1.8% S, 1.45% P). Analysis showed that some of the “sulfate” found in the scrubbing water was actually sulfide (including hydrogen sulfide) and was the main cause of corrosion.

This article describes the failure characteristics of high-pressure long-distance pipelines. It discusses the causes of pipeline failures and the procedures used to investigate them. The use of fracture mechanics in failure investigations and in developing remedial measures is also reviewed.

This article discusses the failure analysis of several steel transmission pipeline failures, describes the causes and characteristics of specific pipeline failure modes, and introduces pipeline failure prevention and integrity management practices and methodologies. In addition, it covers the use of transmission pipeline in North America, discusses the procedures in pipeline failure analysis investigation, and provides a brief background on the most commonly observed pipeline flaws and degradation mechanisms. A case study related to hydrogen cracking and a hard spot is also presented.

This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

This article addresses the forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. It describes the mechanisms of corrosive attack for specific forms of corrosion such as galvanic corrosion, uniform corrosion, pitting and crevice corrosion, intergranular corrosion, and velocity-affected corrosion. The article contains a table that lists combinations of alloys and environments subjected to selective leaching and the elements removed by leaching.

Corrosion is the electrochemical reaction of a material and its environment. This article addresses those forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. Various forms of corrosion covered are galvanic corrosion, uniform corrosion, pitting, crevice corrosion, intergranular corrosion, selective leaching, and velocity-affected corrosion. In particular, mechanisms of corrosive attack for specific forms of corrosion, as well as evaluation and factors contributing to these forms, are described. These reviews of corrosion forms and mechanisms are intended to assist the reader in developing an understanding of the underlying principles of corrosion; acquiring such an understanding is the first step in recognizing and analyzing corrosion-related failures and in formulating preventive measures.

During the installation of power transmission lines across a major interstate highway, a temporary anchor stabilizing one of the poles failed, resulting in the loss of the pole and the associated power lines. It also contributed to a single vehicle incident on the adjacent roadway. Post-failure analysis revealed that the fracture was precipitated by a preexisting weld-related crack. Closed form and numerical stress analyses were also conducted, with the results indicating that the anchor was installed properly within the parameters intended by the manufacturer.

To forged AISI 4140 steel trailer kingpins fractured after 4 to 6 months of service. Fractographic and metallographic examination revealed that cracks were present in the spool-flange shoulder region of the defective kingpins prior to installation on the trailers. The cracks grew and coalesced during service. Consideration of the manufacturing process suggested that the cracks were the result of overheating of the kingpin blanks prior to forging, which was exacerbated during forging by deformation heating in the highly-strained region. This view was supported by results of two types of tensile tests conducted near the incipient melting temperature at the grain boundaries. All kingpins made by the supplier of the fractured ones were ultrasonically inspected and six more anticipated to fail were found. It was recommended that the heating of forging blanks be more carefully controlled, especially with respect to the accuracy of the optical pyrometer temperature readout. Also, procedures must be developed such that forging blanks that trigger the over-temperature alarm are reliably and permanently removed from the production line.

This article describes the preliminary stages and general procedures, techniques, and precautions employed in the investigation and analysis of metallurgical failures that occur in service. The most common causes of failure characteristics are described for fracture, corrosion, and wear failures. The article provides information on the synthesis and interpretation of results from the investigation. Finally, it presents key guidelines for conducting a failure analysis.

Gross wastage and embrittlement were observed in plain carbon steel desuperheaters in five new Naval power plants. The gross wastage could be duplicated in laboratory bomb tests using sodium hydroxide solutions and was concluded to be caused by free caustic concentrated by high heat flux. The embrittlement was shown to be caused by the flow of corrosion generated hydrogen which converted the cementite to methane which nucleated voids in the steel. A thermodynamic estimate indicated that a small amount of chromium would stabilize the carbides against decomposition by hydrogen in this temperature range, and laboratory tests with 2-14% Cr steel verified this.