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ASME PTB-8-2014 pdf download

4.1 SA-20, General Requirements for Steel Plates for Pressure Vessels SA-20 includes general requirements for pressure vessel plate specifications that are listed in the Scope. That includes requirements for terminology, ordering information, materials and manufacture, heat treatment, chemical composition, metallurgical structure, quality, test methods, tension tests, notch toughness tests, identification of plates, permissible variations in dimensions or mass, inspection and testing, retests, retreatment, rejection, test reports, and packaging, marking, and loading for shipment. The following are comments on several of these requirements: (a) Manufacture – Practically all steel in modern steel mills is now produced by strand casting. However, ingots are still used for producing thick plates. Strand cast slabs are limited to about 10 to 12 inches maximum thickness, which limits the final plate thickness to about 4 inches after reduction. SA-20 contains alternative rules that may be used to produce plate using strand cast slabs in thicknesses to about 6 inches. (b) Heat Treatment – The heat treatment (normalizing, quenching and tempering, thermomechanical processing) is specified in the general product specification. ASTM and ASME specifications do not consider “normalized rolling” (permitted by the European (EN) specifications for pressure vessel plates) to be an acceptable substitute for “normalizing”. (c) Chemical Composition – In addition to the elements specified in the applicable product specification, SA-20 requires determination of the content of the following elements: carbon, manganese, phosphorus, sulfur, silicon, nickel, chromium, molybdenum, copper, vanadium, columbium, and in some cases aluminum or other austenitic grain refining element. The chemical composition may include other unspecified elements that may not be listed in the chemical composition tables of the product specification but, if present in excessive amounts can increase hardenability or decrease weldability. SA-20 imposes maximum limits (SA-20 specifications, Table 1) for certain elements (copper, nickel, chromium, molybdenum, vanadium, columbium, titanium, and boron) that may be present but are not listed in the product specification. Excessive amounts of these elements can cause martensitic hardening in heat affected zones during postweld heat treatment with a corresponding loss of notch toughness and can lead to an increased risk of hydrogen-delayed cracking. (d) Tension and Impact Testing – SA-20 includes detailed requirements for tension testing and impact testing most of which is referenced in the product specifications and is referred to the general requirements specification for testing requirements. (e) Quality – SA-20 includes specific requirements for defects and states that plates shall be free of injurious defects. It goes on to state that injurious surface imperfections shall be removed by the manufacturer or processor. Unfortunately, SA-20 does not define “injurious defects”, however it is generally understood that a plate with an “injurious defects” is not suitable for the intended service. Code users may want to consider adding a definition of injurious surface imperfections to their material specifications if it is critical to their application. SA-20 also includes acceptance criteria for edge defects. (f) Repair by Welding – SA-20 includes specific requirements for repair welding. Repair welding is not permitted unless approved the purchaser. (g) Identification of Plates – SA-20 includes requirements for marking of plates. Heat treated plates shall be marked with the letters “MT” and “green” plates (to be heat treated by others) be marked with the letter “G”. SA-20 also specifies the types of required marking and location of markings. (h) Test Reports – The manufacturer or processor shall report the results of all tests required by the applicable product specification, the applicable supplementary requirements, and the purchase order. The test report shall clearly identify the organization submitting the test report. Copies of the original manufacturer’s test report shall be included with any subsequent test report. Test reports may be provided in electronic form.

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