The horizontal heat-exchanger tubes made of copper alloy C70600, in one of two hydraulic-oil coolers in an electric power plant, leaked after 18 months of service. River water was used as the coolant in the heat-exchanger tubes. Several nodules on the inner surface and holes through the tube wall, which appeared to have formed by pitting under the nodules, were revealed by visual examination. Steep sidewalls, which indicated a high rate of attack, were revealed by microscopic examination of a section through the pit which had penetrated the tube wall. The major constituent of reddish deposit on the inner surfaces of the tubes was revealed to be iron oxide and slight manganese dioxide. Effluent from steel mills upstream was indicated by the presence of these and other constituents to be the source of most of the solids found in the tubes. It was concluded that the tubing failed by crevice corrosion. The tubing in the cooler was replaced, and cooling-water supply was changed from river to city water, which contained no dirt to deposit on the tube surfaces. An alternate solution of installing replacement tubes in the vertical position to make deposition of solids from river water less likely was suggested.

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.

The brine-heater shell in a seawater-conversion plant failed by bursting along a welded joint connecting the hot well (C70600 per ASTM B 466) to the heater shell (ASTM A285, grade C steel). Three cracks in the welded joints between the heater shell and the hot well were revealed by visual inspection. It was observed that crack 1 and 2 were covered with high-temperature oxidation products which revealed that the surfaces had been separated for quite some time. A very high discontinuity stress which existed at the longitudinal welds between the hot well and the heater shell was revealed by stress analysis. It was interpreted that the cracks had originated shortly after the heater was put into operation and propagated slowly initially. The rate of propagation was interpreted to have increased due to discontinuity stresses greater than yield strength of the material. It was concluded that the brine heater cracked and fractured because it was overstressed in normal operation. The heater design was modified to make the heater shell and the hot well two separate units. A relief valve was recommended in the heater or in the steam line near the heater.

The failure of a 90-10 cupronickel heat exchanger tube resulted in flooding of the vessel and subsequently sinking it. The corrosion of the cupronickel alloy was facilitated by the high sulfur content of the seawater in which it operated. The failure modes were anodic dissolution and copper reprecipitation.

After about 17 years in service, copper alloy C27000 (yellow brass, 65% Cu) innercooler tubes in an air compressor began leaking cooling water, causing failure and requiring replacement. The tubes were 19 mm in diam and had a wall thickness of 1.3 mm (0.050 in.). The cooling water that flowed through the tubes was generally sanitary (chlorinated) well water; however, treated recirculating water was sometimes used. Analysis (visual inspection, 9x and 75x unetched micrographs, and spectrochemical analysis) showed a thick uniform layer of porous, brittle copper on the inner surface of the tube, extending to a depth of about 0.25 mm (0.010 in.) into the metal, plug-type dezincification extending somewhat deeper into the metal. This supported the conclusion that failure of the tubes was the result of the use of an uninhibited brass that has a high zinc content and therefore is readily susceptible to dezincification. Recommendations included replacing the material with copper alloy C68700 (arsenical aluminum brass), which contains 0.02 to 0.06% As and is highly resistant to dezincification. Copper alloy C44300 (inhibited admiralty metal) could be an alternative selection for this application; however, this alloy is not as resistant to impingement attack as copper alloy C68700.

Admiralty brass (Alloy C44300) cooling tubes which were part of a heat exchanger in a turbogenerator that provided electricity to a manufacturing plant failed. A mixture of non-recirculating city and “spring pit” water flowed through bundles of tubes to cool the oil in which they are immersed. However, a problem developed when several of the brass tubes cracked transversely, allowing cooling water to mix with the oil. The presence of a tensile stress, intergranular cracks, and a corrosion product suggested the tube failures resulted from stress-corrosion cracking. The main corrosion product was cupric hydroxychloride. In addition to switching to a more corrosion-resistant alloy, extreme care should be taken in the manufacturing of the replacement tube bundles to avoid imparting any residual tensile stresses in the tubing. Analyses of city and spring-pit water were recommended also, to determine which contained the least-harmful corrosive chemicals.

Inhibited admiralty brass (UNS C44300) condenser tubes used in a natural-gas-fired cogeneration plant failed during testing. Two samples, one from a leaking tube and the other from an on leaking tube, were examined. Chemical analyses were conducted on the tubes and corrosion deposits. Stress-corrosion cracking was shown to have caused the failure. The most probable corrosive was ammonia or an ammonium compound in the presence of oxygen and water. All of the tubes were replaced.

This article describes the characteristics of tubing of heat exchangers with respect to general corrosion, stress-corrosion cracking, selective leaching, and oxygen-cell attack, with examples. It illustrates the examination of failed parts of heat exchangers by using sample selection, visual examination, microscopic examination, chemical analysis, and mechanical tests. The article explains corrosion fatigue of tubing of heat exchangers caused by aggressive environment and cyclic stress. It also discusses the effects of design, welding practices, and elevated temperatures on the failures of heat exchangers.

Heat exchangers are devices used to transfer thermal energy between two or more fluids, between a solid surface and a fluid, or between a solid particulate and a fluid at different temperatures. This article first addresses the causes of failures in heat exchangers. It then provides a description of heat-transfer surface area, discussing the design of the tubular heat exchanger. Next, the article discusses the processes involved in the examination of failed parts. Finally, it describes the most important types of corrosion, including uniform, galvanic, pitting, stress, and erosion corrosion.

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 article explains the main types and characteristic causes of failures in boilers and other equipment in stationary and marine power plants that use steam as the working fluid with examples. It focuses on the distinctive features of each type that enable the failure analyst to determine the cause and suggest corrective action. The causes of failures include tube rupture, corrosion or scaling, fatigue, erosion, and stress-corrosion cracking. The article also describes the procedures for conducting a failure analysis.

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.