Service environments, effect

Nondestmctive tests differ from methods of laboratory analysis and testing where specimens are generally sectioned, broken, damaged, or destroyed. Nondestmctive tests can be performed on materials, components, and stmctures or systems that actually are to be used. Thus, effective use of NDE requires engineering knowledge of the stmcture, the performance characteristics, and service environment, as well as the test method. More complete information on all of the topics discussed herein are available (1 6). 

One of the most effective methods of preventing corrosion is the selection of the proper metal or alloy for a particular corrosive service. Once the conditions of service and environment have been determined that the equipment must withstand, there are several materials available commercially that can be selected to perform an effective service in a compatible environment. Some of the major problems arise from popular misconceptions for example, the use of stainless steel. Stainless steel is not stainless and is not the most corrosion-resistant material. Compatibility of material with service environment is therefore essential. For example, in a hydrogen sulfide environment, high-strength alloys (i.e., yield strength above 90,000 psi or Rc 20 to 22) should be avoided. In material selection some factors that are important to consider are material s physical and chemical properties, economics and availability. 

With some materials, there are specific heat treatments that are known to reproduce the worst effects of the heat of welding. It is recommended, therefore, that in tests made to qualify a material for a particular service environment, in addition to the exposure of welded test specimens in order to observe effects of welding heat, specimens should be included that have been given a controlled abusive or sensitising heat treatment. As an illustration, austenitic stainless steels may be held at 650-700° forO-5-1 h, followed by testing for susceptibility to intercystalline attack as in ISO 3651-1 or -2 1976. 

Establish final design criteria Allowable stresses, strains, deflections Margins of safety against local and overall instability, vibrations, etc. Take into account type and duration of load, service environments, process effects, equality expectations... 

Test materials for structural properties and effect of service environment... 

McNicol, D.K. Bendell, B.E. and Ross, R.K. Studies of the effects of acidification on aquatic wildlife in Canada Waterfowl and Trophic Relationships in Small Lakes in Northern Ontario, Occasional Paper No. 62, Canadian Wildlife Service, Environment Canada, Ottawa, Ontario, 1987, pp 76. 

Moisture degradation of adhesive bonds occurs within the bulk adhesive material, at the adhesive-adherend interface, and within certain substrates. These degradation mechanisms are discussed below. Particularly insidious is the effect of the combined elements of moisture, stress, and temperature. Unfortunately, this synergistic effect occurs at relatively low temperatures, and such a service environment is common to many adhesive applications. For these reasons, this combined environment is given special focus in Sec. 15.5.2. 

Environmental aging is usually less severe in service (laboratory tests tend to accelerate aging so that the testing can be completed in a reasonable time). However, the effects of the actual service environment are generally more complex. For example, there may be simultaneous exposure to cyclic stress, cyclic temperature, and humid environments. 

Chapters 15 and 16 describe formulations that have been specifically developed for use in certain service environments and with certain substrates. The effects of the environmental... 

Despite the severity of the problems associated with environmental degradation of mechanical properties, it is only recently that the ceramic composites community has begun to address them. In the following section, some of the approaches that attempt to inhibit the adverse effects of service environments are discussed for specific composite systems, and the relative effectiveness is assessed. 

The effect of composition, the nature, and the ratios of the constituents on the properties of paints, are factors of utmost importance in paint formulations. An indication of likely service environment, life expectancy of the coatings, method of application, color, surface finish, drying time, and cost are also taken into consideration. All of this information. 

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