A welded joint between lengths of 4 in. OD x 13 SWG copper pipe which formed part of a cold-water main failed by cracking over one-third of the circumference. Microscopic examination of the filler metal showed that it had a structure corresponding to a brass of the 60:40 type commonly used for bronze welding. Failure resulted from dezincification of the joint material from the internal side of the tube. Also, a selective attack on the beta phase had occurred. It was evident that the loss in mechanical strength arising from the corrosion had resulted in the development of cracking in service. The filler metal used was not resistant to the conditions to which it was exposed. Copper welding rods as per BS 1077 or a Cu-Ag-P brazing alloy as recommended in BS 699, would have been preferable.

A 25 mm (1 in.) copper coupling had been uniformly degraded around most of the circumference of the bell and partially on the spigot end. One penetration finally occurred through the thinned area on the spigot end of the pipe. Investigation supported the conclusion that although the pipe was buried in noncorrosive sandy soil, it was found to incur stray currents at 2 Vdc in relation to a Cu/CuSO4 half cell. Recommendations included eliminating, moving, or shielding the source of stray current.

In a copper hot water system, a bent pipe was soldered into a straight pipe with twice the diameter. The neighborhood of the soldered joint was covered with corrosion product predominantly blue-green in color, presumably carbonates. When these corrosion products were scratched off it was seen that the copper beneath this layer had not suffered noticeable attack. The object of the examination was the localized deep cavities located almost symmetrically to both sides of the inserted end of the narrower tube on the internal wall of the wider tube which had in one place been eaten right through. The symmetrical location on each side of the point of insertion of the narrower pipe and the localized sharp delineation of the attack indicated erosion due to the formation of turbulence. By avoiding sharp transitions and abrupt changes in cross section it is possible to design the pipe work so that localized turbulence is obviated. Degassing and cleansing of the water also would reduce the danger of erosion particularly in the case of softened water, which takes up oxygen and carbon dioxide very readily thus becoming particularly aggressive.

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.

Copper piping in a closed-loop water heater system was found to be corroded with MIC and erosion of the weak oxide layer. Investigation (visual inspection, bacterial corrosion cultures, and 20x/400x micrographs) supported the conclusion that the corrosion was caused by microbiological attack, specifically sulfur-reducing bacteria. No recommendations were made.

A residential subdivision near Tampa, FL was constructed in 1984 through 1985. Several sections of copper pipe were removed from one residence that had reported severe leaking. Visual examination revealed extensive pitting corrosion throughout the ID surfaces of the sample. Microscopic evaluation of a cross section of a copper pipe revealed extensive pitting corrosion throughout the inner diametral surfaces of the pipe. Some pits had penetrated through the wall thickness, causing the pin hole leaks. Analysis of a sample of water obtained from the subdivision revealed relatively high hardness levels (210 mg/l), high levels of sulfate ions (55 mg/l), a pH of 7.6 and a sulfate-to-chloride ratio of 3:1. Analysis of corrosion product removed from the ID surfaces of the pipe section revealed that an environment rich in carbonates existed inside the pipe, a result of the hard water supply. It was concluded that pitting corrosion was a result of the corrosive waters supplied by the local water utility. Waters could be rendered non-pitting by increasing their pH to 8 or higher and neutralizing the free carbon dioxide.

Soft-soldered copper pipe joints used in refrigerating plants failed. The solder had not adhered uniformly to the pipe surface. In addition, there were some longitudinal grooves on the pipe surfaces, parts of which were not filled with solder. The unsoldered areas formed cavities within the joints, some of which had been in direct communication with the outsides via the grooves or interconnected cavities. On cooling, moisture condensed on the external surfaces. Some of this was drawn by capillary action into the cavities in open communication with the external surface. On continued cooling to below freezing-point, water that entered the cavities solidified. This was accompanied by a slight increase in volume, which collapsed the pipe walls. In the examples, the pipe ends had not been properly tinned. The solder used was found to be of the tin-antimony type, containing about 5% antimony, which is more difficult to use than the usual tin-lead alloys. The use of this particular type of solder was a contributory factor in the production of unsound joints in the samples examined.

A T-piece from a copper hot water system failed. Microscopic examination of a polished section revealed a main crack and branching transcrystalline cracks running from the outer surface of the pipe into the pipe wall. The crack appearance indicated disintegration by stress-corrosion cracking. Although copper is not susceptible in the pure state, it is prone to stress-corrosion cracking under tensile stress in the presence of other elements in a damp ammoniacal atmosphere. The material was not defective, but a phosphorus-deoxidized copper type. The residual phosphorus combined with oxygen to form phosphorus pentoxide. Hard soldering in turn prevented the formation of cuprous oxide, and hydrogen embrittlement occurred.

An investigation was conducted to determine why 16 out of 139 pipe bends cracked during hot induction bending. The pipe conformed to API 5L X65 PSL2 line pipe standards and measured 1016 mm (40 in.) in diam with a wall thickness of 18.5 mm. A metallurgical cross section was removed along a crack on the extrados to document the crack morphology using optical microscopy. In addition to cracking, golden-yellow streaks were visible at the extrados, and the composition was examined using scanning electron microscopy with energy dispersive spectroscopy. Based on the results, investigators concluded the pipe was contaminated with copper at the mill were it was produced.

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.

A failure occurred in buried brass (92% Cu, 8% Zn) piping used to carry drinking water in wet clay soil after less than two years in service. Investigation (visual inspection, chemical analysis of both the pipe surface and water, and a comparison of the corrosion failure of power station condenser tubing cooled by seawater for two copper alloys, an aluminum brass alloyed with arsenic (UNS C68700, ASTM B111, or Cu-Zn-20Al DIN17660), and a cupronickel 70-30 alloy with iron added (C71500, ASTM B111, or Cu-Ni-30Fe DIN17665)) supported the conclusion that the failure was caused by microbial induced corrosion by sulfate-reducing bacteria. No recommendations were made.

A straight-tube cooler type heat exchanger had been in service for about ten years serving a coal pulverizer in Georgia. Non-potable cooling water from a local lake passed through the inner surfaces of the copper tubing and was cooling the hot oil that surrounded the outer diametral surfaces. Several of the heat exchangers used in the same application at the plant had experienced a severe reduction in efficiency in the past few years. One heat exchanger reportedly experienced some form of leakage following discovery of oil contaminating the cooling water. This heat exchanger was the subject of a failure investigation to determine the cause and location of the leaks. Corrosion products primarily contained copper oxide, as would be expected from a copper tubing. The product also exhibited the presence of a significant amount of iron oxides. Metallographic cross sectioning of the tubes and microscopic analysis revealed several large and small well rounded corrosion pits present at the inner diametral surfaces. The cause of corrosion was attributed to corrosive waters that were not only corroding the copper, but were corroding steel pipes upstream from the tubing.

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.

Several cases of embrittlement failure are analyzed, including liquid-metal embrittlement (LME) of an aluminum alloy pipe in a natural gas plant, solid metal-induced embrittlement (SMIE) of a brass valve in an aircraft engine oil cooler, LME of a cadmium-plated steel screw from a crashed helicopter, and LME of a steel gear by a copper alloy from an overheated bearing. The case histories illustrate how LME and SMIE failures can be diagnosed and distinguished from other failure modes, and shed light on the underlying causes of failure and how they might be prevented. The application of LME as a failure analysis tool is also discussed.

Six cases of failure attributed to microbiologically influenced corrosion (MIC) were analyzed to determine if any of the failures could have been avoided or at least predicted. The failures represent a diversity of applications involving typical materials, primarily stainless steel and copper alloys, in contact with a variety of liquids, chemistries, and substances. Analytical techniques employed include stereoscopic examination, energy dispersive x-ray spectroscopy (EDS), temperature and pH testing, and metallographic analysis. The findings indicate that MIC is frequently the result of poor operations or improper materials selection, and thus often preventable.

Erosion occurs as the result of a number of different mechanisms, depending on the composition, size, and shape of the eroding particles; their velocity and angle of impact; and the composition of the surface being eroded. This article describes the erosion of ductile and brittle materials with the aid of models and equations. It presents three examples of erosive wear failures, namely, abrasive erosion, erosion-corrosion, and cavitation erosion.

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.

Visual examination, using the unaided eye or a low-power optical magnifier, is typically one of the first steps in a failure investigation. This article presents the guidelines for selecting samples for scanning electron microscope examination and optical metallography and for cleaning fracture surfaces. It discusses damage characterization of metals, covering various factors that influence the damage, namely stress, aggressive environment, temperature, and discontinuities.

Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, an impinging liquid, or impinging solid particles. The detrimental effects of erosion have caused problems in a number of industries. This article describes the processes involved in erosion of ductile materials, brittle materials, and elastomers. Some examples of erosive wear failures are given on abrasive erosion, liquid impingement erosion, cavitation, and erosion-corrosion. In addition, the article provides information on the selection of materials for applications in which erosive wear failures can occur.