Friday, June 10, 2011

MATERIAL SPECIFICATIONS

It's been a busy day in the factory and I'm not too health either, but I have to post for Piping & Fabrication first and today it's about Material Specifications. The American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE) have devised a standardized numbering system for the various classes of carbon and alloy steels that has gained widespread acceptance in North America.

This system employs a four-digit number for carbon and low-alloy steels, and a three-digit number for stainless steels. Regarding the former, the first two digits represents the major alloying elements of the grade. The final two digits represent the nominal carbon content of each alloy, in hundreds of weight percent. For example, 10XX represents simple carbon steels, and 41XX stands for steels with chromium-molybdenum as the major alloying elements. In both classes, a specific grade possessing a nominal carbon content of 0.20 percent would be, respectively, 1020 and 4120. In this fashion the many possible alloy steels can be systematically identified.

Table A3.4 lists the carbon and alloy steel grades categories recognized by AISI and SAE.

TABLE A3.4 Carbon and Alloy Steel Grade Categories: AISI, SAE, UNS


TABLE A3.5 Selected Piping System Materials—ASME Specifications
TABLE A3.6 Cross-Reference for ASME to UNS Selected Pipe and Tubing Specifications
TABLE A3.7 Nominal Compositions of Wrought Copper Material

The stainless steels are assigned a three-digit code by AISI. Those austenitic stainless steels composed of chromium, nickel, and manganese are the 2XX series. Chromium-nickel austenitic stainless steels are 3XX; ferritic and martensitic stainless steels are 4XX. In the case of stainless steels, the last two digits represent a unique overall composition rather than the level of carbon.

Due to increasing international technical community involvement and cooperation, and with each country possessing its own alloy numbering system, a worldwide universal system of material identification was needed. The Unified Numbering System (UNS) was the result. In this system a letter is followed by a five-digit number which, taken together, uniquely defines each particular composition. Many of the conventions adopted in the AISI/SAE system were incorporated into the UNS numbers, as shown on Table A3.4.

The AISI and SAE specifications for alloys controls only material composition. Addition control over minimum properties, heat treatment, and other inspections was necessary to assure reproducibility and reliability of the materials for their intended purpose. The American Society for Testing and Materials (ASTM), the American Society of Mechanical Engineers (ASME), and the American Petroleum Institute (API) have generated a series of comprehensive material specifications that extend this control. Table A3.5 lists the more common ASME specification and grade numbers for the common piping system materials of construction. Table A3.6 gives equivalencies between selected piping material grades in ASME with the Unified Numbering System (UNS).

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