Laboratory photography in a controlled setting should also be performed to guarantee accurate reproduction of color tones and surface textures The type and extent of on-site sampling depends on the environment and its availability. Piping corrosion in a domestic water service would require water samples from the source(incoming water supply )and from the end use(for example, a faucet). Microbiologically influenced corrosion may apply in certain cases. On-site testing or sample removal is necessary to retain the most accurate information regarding the type and number of bacteria involved. In most cases, removal of corrosion deposits from the surface may be performed in the field If the sample is undergoing extensive laboratory examination, it may be prudent to carefully retain the corrosion in place for laboratory documentation and removal If samples are removed on site, care must be taken to avoid any contamination. Sealed bags, latex gloves, tools for sample removal, buffered containers for water samples, MIC kits, and adhesive tape are useful for sample removal. (See the article"Biological Corrosion Failures" in this Volume for listings of commercially available kits. The analyst should avoid touching any corrosion product directly with bare hands to prevent contamination Physical removal of samples must be done in a manner to avoid further damage to the failed component and to avoid disturbance of corrosion products. In general, cutting must be done with care to avoid alterations of the metallurgical condition of the material and corrosion deposits. Saw cutting is generally preferred over torch cutting, since heating of the sample can affect the material and the corrosion product. If torch cutting is performed, a distance of 75 to 150 mm(3 to 6 in. )should be maintained from the area of interest. Saw cutting should be performed at a slow rate to avoid overheating. Use of lubricants and coolants should be avoided, if possible, to minimize contamination The proper shipment and storage of samples lessens the possibility of destruction of pertinent evidence Wrapping and sealing of the failed component will generally retain evidence and prevent further oxidation or contamination. A neutral environment may be required to reduce activity. Any fracture surfaces should be otected from the potential of rubbing and contact Laboratory Examination. While each type of failure may have unique tests, some general steps should be taken in investigating all corrosion failures All samples must be properly identified and their origin, handling, and processing within the laboratory Photographs should document samples in the "as-received"condition Stereomicroscopic examination of the involved areas should follow. Photographic documentation during stereomicroscopy should also be performed Nondestructive test methods should now be considered. The key to performing nondestructive testing is to avoid any disturbance of scale product until corrosion samples have been removed. Radiography to document casting quality or to evaluate cracking is usually acceptable. However, the use of liquids or dyes is not acceptable until the corrosion samples have been removed The removal of corrosion deposits for evaluation is the next step. The samples should be removed with a noncontaminating tool such as a stainless steel pick. Corrodent samples should be placed in clean, clearly marked containers The corrosion deposits should be analyzed. One of the most common analysis techniques is energy dispersive spectroscopy(EDS). This method, used in conjunction with scanning electron microscopy (SEM), provides information regarding the elemental composition of the corrosion deposit Based on the visual examination, a corrosion sample may need to be subjected to microbiological nal These steps may be followed by cleaning and/or other tests After the corrosion deposits selected for examination have been secured, the failure sample may be cleaned However, in some cases it may be desirable to retain the corrosion product intact for metallographic examination. For instance, a component subject to hydrogen damage or caustic corrosion may benefit from an analysis of the corrosion product layering effect. Cross sections should be taken prior to removal of corrosion p Precautions must be taken during the cleaning process to avoid any destruction to the base metal. Generally, the least aggressive cleaning method is initiated first, such as brushing with a soft brush or light air pressure Thefileisdownloadedfromwww.bzfxw.comLaboratory photography in a controlled setting should also be performed to guarantee accurate reproduction of color tones and surface textures. The type and extent of on-site sampling depends on the environment and its availability. Piping corrosion in a domestic water service would require water samples from the source (incoming water supply) and from the end use (for example, a faucet). Microbiologically influenced corrosion may apply in certain cases. On-site testing or sample removal is necessary to retain the most accurate information regarding the type and number of bacteria involved. In most cases, removal of corrosion deposits from the surface may be performed in the field. If the sample is undergoing extensive laboratory examination, it may be prudent to carefully retain the corrosion in place for laboratory documentation and removal. If samples are removed on site, care must be taken to avoid any contamination. Sealed bags, latex gloves, tools for sample removal, buffered containers for water samples, MIC kits, and adhesive tape are useful for sample removal. (See the article “Biological Corrosion Failures” in this Volume for listings of commercially available kits.) The analyst should avoid touching any corrosion product directly with bare hands to prevent contamination. Physical removal of samples must be done in a manner to avoid further damage to the failed component and to avoid disturbance of corrosion products. In general, cutting must be done with care to avoid alterations of the metallurgical condition of the material and corrosion deposits. Saw cutting is generally preferred over torch cutting, since heating of the sample can affect the material and the corrosion product. If torch cutting is performed, a distance of 75 to 150 mm (3 to 6 in.) should be maintained from the area of interest. Saw cutting should be performed at a slow rate to avoid overheating. Use of lubricants and coolants should be avoided, if possible, to minimize contamination. The proper shipment and storage of samples lessens the possibility of destruction of pertinent evidence. Wrapping and sealing of the failed component will generally retain evidence and prevent further oxidation or contamination. A neutral environment may be required to reduce activity. Any fracture surfaces should be protected from the potential of rubbing and contact. Laboratory Examination. While each type of failure may have unique tests, some general steps should be taken in investigating all corrosion failures: · All samples must be properly identified and their origin, handling, and processing within the laboratory documented. · Photographs should document samples in the “as-received” condition. · Stereomicroscopic examination of the involved areas should follow. Photographic documentation during stereomicroscopy should also be performed. · Nondestructive test methods should now be considered. The key to performing nondestructive testing is to avoid any disturbance of scale product until corrosion samples have been removed. Radiography to document casting quality or to evaluate cracking is usually acceptable. However, the use of liquids or dyes is not acceptable until the corrosion samples have been removed. · The removal of corrosion deposits for evaluation is the next step. The samples should be removed with a noncontaminating tool such as a stainless steel pick. Corrodent samples should be placed in clean, clearly marked containers. · The corrosion deposits should be analyzed. One of the most common analysis techniques is energy￾dispersive spectroscopy (EDS). This method, used in conjunction with scanning electron microscopy (SEM), provides information regarding the elemental composition of the corrosion deposit. · Based on the visual examination, a corrosion sample may need to be subjected to microbiological analysis. · These steps may be followed by cleaning and/or other tests. After the corrosion deposits selected for examination have been secured, the failure sample may be cleaned. However, in some cases it may be desirable to retain the corrosion product intact for metallographic examination. For instance, a component subject to hydrogen damage or caustic corrosion may benefit from an analysis of the corrosion product layering effect. Cross sections should be taken prior to removal of corrosion products. Precautions must be taken during the cleaning process to avoid any destruction to the base metal. Generally, the least aggressive cleaning method is initiated first, such as brushing with a soft brush or light air pressure. The file is downloaded from www.bzfxw.com