Subgroup on General Requirements

Subgroup on Fabrication and Examination

FIGURE 12.7 Organization of ASME Boiler and Pressure and Pressure Vessel Code.

FIGURE 12.7 Organization of ASME Boiler and Pressure and Pressure Vessel Code.

and >1103 kPa (160 psi) pressures and/or >121°C(250°F) temperatures forhigh-temperature water boilers. The scope of jurisdiction of Section I is the boiler proper and the boiler external piping.

Of particular interest for advanced materials producers is the subgroup on materials in Section I, which limits materials to (1) those listed in Section II and (2) those listed in certain tables in Section I. In addition, certain materials are restricted in regard to usage. For example, an austenitic stainless steel might not be permitted for parts in water-wetted service but may be permitted for steam-touched service. Also included in Section I, are provisions for approval of new materials for code construction:

1. New materials shall have been previously adopted by ASTM (adoption of a new materials for the ASME code means adoption of the ASTM

specification for the material).

2. Items to be furnished for evaluation by the code committee are:

a. Such mechanical properties as ultimate tensile strength, yield strength, creep and rupture strength, heat treatment, toughness, etc.

b. Stress-strain data for vessels designed for external pressure c. Weldability, including data for establishing the requirements of Section IX Welding d. Physical changes and resistance to effects of both elevated temperature and cryogenic temperature where applicable e. Availability of the material regarding patents and licensing

For design purposes, two approaches are prescribed in the code: design by rule and design by analysis. Section I relies primarily on design by rule, which is basically an empirical approach (what has proven to work successfully in the past) setting limits on: factors of safety (typically 4-5); design pressures and temperatures, minimum thicknesses [6.35 mm (0.25 in.)]; maximum pressures [no greater than 1.06 times the maximum allowable working pressure (use of safety valves required)]; loadings due to internal pressures (these set the minimum required thicknesses unless other loadings exceed 10% of the allowable working stress); thickness of cylindrical components under internal pressure as determined from formulas; openings and reinforcements; fatigue, fast-fracture, creep, and other failure mechanisms; and hydrostatic proof tests (1.5 times the maximum allowable working pressure). Note, that Section III Nuclear Power Plant Components uses the more sophisticated, but less historically based, design by analysis. The use of design by analysis in Section III is a precedent important for acceptance of CFCCs in the code since these materials may require recently developed reliability techniques employing computer algorithms for implementation in advanced designs.

Finally, Section I requires affixing a special code stamp and a proper nameplate to the components and resulting system, respectively, after complying with all the code requirements of design and construction. To document compliance, seven types of Manufacturers Data Report Forms must be completed.

Section II also has its roots in the original 1914 edition of the code. The original materials specifications were developed in a joint effort of ASME and ASTM for ferrous and nonferrous materials. In addition, joint specifications with the American Welding Society (AWS) have since been developed for welding rods, electrodes, and filler metals. Only those ASTM or AWS specifications required by ASME are addressed in Section II. The documentation of Section II is a four-part compendium of materials data: Part A—Ferrous Materials Specifications, Part B—Nonferrous Material Specifications, Part C—Specification for Welding Rods, Electrodes, and Filler Metals, and Part D—Properties. Part D lists material properties for all materials accepted by Sections I, III, and VIII. Not only are mechanical properties but also physical properties are contained in Part D. However, a major portion of the data contained in Part D are tables of stresses as functions of temperature.

Currently, certain advanced materials such as monolithic and composite advanced composites are not currently allowed materials in the ASME Boiler and Pressure Vessel Code. For a manufacturer wishing to implement CFCC materials in a code-certified power boiler design, several steps must be taken. First, the CFCC material of interest must receive a specification from ASTM, including materials analysis, physical properties, and mechanical properties. Second, the material must be accepted by the code as an allowable material. Third, the design-by-analysis approach used by the manufacturer must be shown to meet the minimum requirements of Section I. Fourth, the manufacturing process that includes the CFCC material must be certified as being acceptable under the code. Fifth, special nondestructive characterization procedures now being developed for CFCCs must be certified as under Section V Nondestructive Examination. Sixth, the system must be constructed using the approved methods and material, ultimately passing a pressurized proof test as per the code requirements before receiving official certification.

Military Handbook 17 Mil-Hdbk-17 is the outgrowth of a collaborative effort on the part of industry (i.e., defense contractors) and the U.S. Department of Defense to clarify and codify issues involving the use of polymer matrix composites (PMCs) in advanced designs. Mil-Hdbk-17 has been in existence in various forms since 1959 and has been relatively successful in creating common language, design philosophies, fabrication methods, maintenance approaches, and certification of advanced PMCs. Recent directives from the U.S. Department of Defense have established the format for developing offshoots of Mil-Hdbk-17 for other advanced composites, namely, metal matrix composites (MMCs) in 1993 and ceramic matrix composites (CMCs) in 1996. The organization of the Mil-Hdbk-17 effort for CMCs is shown in Fig. 12.8.

The vision of the Mil-Hdbk-17 effort for CMCs is as follows: Mil-Hdbk-17 is the primary and authoritative source for characterization, statistically based property, and performance data of current and emerging ceramic matrix composites. It reflects the best available data and methodologies for characterization, testing, analysis and design and usage guidelines in support of design methodologies for composites.

The objectives are:

• Development of a framework for the future, successful use of CMCs.

• Provide guidance to industry for the collection of statistically meaningful critical data that designers need to utilize CMCs.

FIGURE 12.8 Organization of Mil-Hdbk-17 CMC effort.

• Based on the requirements from the design community. Identify appropriate properties and broadly accepted testing procedures—including consideration of the designation of the precision level and prioritization of properties required.

• Provide guidelines and recommendations for the characterization, testing, design, and utilization of CMC materials and structures.

• Provide the primary and authoritative sources for characterization, property, and performance data of current and emerging CMC systems.

• Provide recommendations for the statistical analysis of materials data and structures relativity.

Data Review Any data generated for inclusion in Mil-Hdbk-17 must satisfy requirements for confidence bounds and statistical sample size within a batch and batch to batch. Because of the need to establish the CMC portion of the Mil-Hdbk-17 as quickly as possible, database generation has been simultaneous with establishing design rules and guidelines. Note also in Fig. 12.8 that while the testing activity is separate, it can actually be thought of as performing a service role to the other activities. Moreover, the stated mission of the testing activity is not to develop standards (this is best left to the standards-writing bodies already discussed), but instead to identify and recommend those existing standards that are appropriate. Where appropriate standards do not exist, the testing activity will assist standards-writing bodies in the development of the standards.

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