corrosion at porous areas exposed at the surface of the metal. Also, Monel metal parts that corroded rapidly in an environment to which Monel is highly resistant actually were strongly magnetic and made of carbon steel. In another instance, failure of a braided copper wire was traced to the substitution of a carbon-black filler for the usual silica filler in a sheath covering the wire. Thus, galvanic action occurred between the carbon and the copper in the presence of moisture While knowledge of the part and its application is desirable in any failure analysis, accurate history is especially important in the investigation of corrosion failures Information about the type of environment to which the failed part was exposed is essential. For instance, corrosion behavior in plants along rivers is affected by both local and upstream chemical composition in the system. Other determining factors include the temperature, whether exposure to the environment is continuous or intermittent and whether these and other factors varied during the service life of the part If available, engineering drawings and material and manufacturing specifications for the part should be examined Particular attention should be given to any part changes that may have been made. Missing information should be obtained from operating and inspection personnel, if possible. At the same time, the accuracy of any relevant documentary information, such as daily log sheets or inspection reports, should be verified. The investigator should determine if any tests or changes affected the physical evidence of the failure On-Site Examination and Sampling On-site examination is generally the same for corrosion failures as for other types of failures. The region of failure itself should be examined visually using hand magnifiers and any other suitable viewing equipment that is available The areas immediately adjacent to and near the failure, as well as related components of the system, should be examined for possible effects on the failure. Remote, related equipment should be examined, especially in complex systems and where liquid or gases flow. Also, the possibility of introducing chemicals or other contaminants from upwind or upstream areas should be checked. In one case, for example, ammonia released to the atmosphere by a neighboring plant lead to the SCC failure of a carbon steel boiler If possible, the failed component and related components of the system should be photographed before samples are practice is to calibrate the color at the beginning of every session by taking a picture of the film box, for example.good Ion Accessories useful in on-site examinations include plastic bags for holding samples, a stainless steel spatula for digging out soft corrosion products, and a file capable of cutting through hard scales. a magnet can distinguish austenitic from martensitic and ferritic stainless steels as well as steels from nonferrous alloys Sampling. When on-site sampling is done, the investigator should be guided by the information already obtained about the history of the failure. The bulk environment to which the failed part was exposed should be sampled, and suitable techniques should be used to obtain samples and make observations(such as pH, for instance)on the local environment at the point of failure In addition to taking samples from the failed area, samples from adjacent areas or apparently noncorroded regions should be obtained for comparison purposes. New or unused parts can provide evidence of the initial or unexposed condition of the part Removal of specimens and samples of corrosion products from the failed part or area requires the utmost caution. Care must be taken to avoid destroying valuable evidence or damaging the part and its related components. For example, torch cutting often is used for removal of specimens because it is fast and convenient. With torch cutting, cuts should be made away from the failure site to prevent alteration of the microstructure, thermal degradation of residues, and introduction of contaminants. If an abrasive cutoff wheel or a saw is used, the same precautions to avoid overheating apply. Also coolants or lubricants that can contaminate or alter the part or any deposits present should not be used After the samples have been extracted, they must be suitably protected during transportation to the laboratory, such as ith glass vials and polyethylene bags. One way to retain deposited material is to tape a covering of inert plastic over the critical area Preliminary laboratory examination The procedures followed in the preliminary laboratory examination will vary, depending on whether an on-site examination has already been performed by the failure analyst and its completeness. An on-site examination by a well- equipped investigator will include much of the work that otherwise would have to be done in the preliminary laboratory examination When no on-site examination has been done, a failure analyst will be aided by records on the part and environment and the remainder of the failed part(or at the very minimum a good photographic record of it). Also helpful are undamaged or unused parts, related components, and samples of the environment Thefileisdownloadedfromwww.bzfxw.comcorrosion at porous areas exposed at the surface of the metal. Also, Monel metal parts that corroded rapidly in an environment to which Monel is highly resistant actually were strongly magnetic and made of carbon steel. In another instance, failure of a braided copper wire was traced to the substitution of a carbon-black filler for the usual silica filler in a sheath covering the wire. Thus, galvanic action occurred between the carbon and the copper in the presence of moisture. While knowledge of the part and its application is desirable in any failure analysis, accurate history is especially important in the investigation of corrosion failures. Information about the type of environment to which the failed part was exposed is essential. For instance, corrosion behavior in plants along rivers is affected by both local and upstream chemical composition in the system. Other determining factors include the temperature, whether exposure to the environment is continuous or intermittent and whether these and other factors varied during the service life of the part. If available, engineering drawings and material and manufacturing specifications for the part should be examined. Particular attention should be given to any part changes that may have been made. Missing information should be obtained from operating and inspection personnel, if possible. At the same time, the accuracy of any relevant documentary information, such as daily log sheets or inspection reports, should be verified. The investigator should determine if any tests or changes affected the physical evidence of the failure. On-Site Examination and Sampling On-site examination is generally the same for corrosion failures as for other types of failures. The region of failure itself should be examined visually using hand magnifiers and any other suitable viewing equipment that is available. The areas immediately adjacent to and near the failure, as well as related components of the system, should be examined for possible effects on the failure. Remote, related equipment should be examined, especially in complex systems and where liquid or gases flow. Also, the possibility of introducing chemicals or other contaminants from upwind or upstream areas should be checked. In one case, for example, ammonia released to the atmosphere by a neighboring plant lead to the SCC failure of a carbon steel boiler. If possible, the failed component and related components of the system should be photographed before samples are removed. Color photographs are highly desirable, especially when colored products of corrosion are present. A good practice is to calibrate the color at the beginning of every session by taking a picture of the film box, for example, using the same lighting conditions. Accessories useful in on-site examinations include plastic bags for holding samples, a stainless steel spatula for digging out soft corrosion products, and a file capable of cutting through hard scales. A magnet can distinguish austenitic from martensitic and ferritic stainless steels, as well as steels from nonferrous alloys. Sampling. When on-site sampling is done, the investigator should be guided by the information already obtained about the history of the failure. The bulk environment to which the failed part was exposed should be sampled, and suitable techniques should be used to obtain samples and make observations (such as pH, for instance) on the local environment at the point of failure. In addition to taking samples from the failed area, samples from adjacent areas or apparently noncorroded regions should be obtained for comparison purposes. New or unused parts can provide evidence of the initial or unexposed condition of the part. Removal of specimens and samples of corrosion products from the failed part or area requires the utmost caution. Care must be taken to avoid destroying valuable evidence or damaging the part and its related components. For example, torch cutting often is used for removal of specimens because it is fast and convenient. With torch cutting, cuts should be made away from the failure site to prevent alteration of the microstructure, thermal degradation of residues, and introduction of contaminants. If an abrasive cutoff wheel or a saw is used, the same precautions to avoid overheating apply. Also, coolants or lubricants that can contaminate or alter the part or any deposits present should not be used. After the samples have been extracted, they must be suitably protected during transportation to the laboratory, such as with glass vials and polyethylene bags. One way to retain deposited material is to tape a covering of inert plastic over the critical area. Preliminary Laboratory Examination The procedures followed in the preliminary laboratory examination will vary, depending on whether an on-site examination has already been performed by the failure analyst and its completeness. An on-site examination by a well￾equipped investigator will include much of the work that otherwise would have to be done in the preliminary laboratory examination. When no on-site examination has been done, a failure analyst will be aided by records on the part and environment and the remainder of the failed part (or at the very minimum a good photographic record of it). Also helpful are undamaged or unused parts, related components, and samples of the environment. The file is downloaded from www.bzfxw.com