SPECIFICATION FOR PRESSURE VESSEL PLATES, ALLOY STEEL, QUENCHED AND TEMPERED 7, 8, AND 9% NICKEL

1. Scope

1.1 This specification covers 7, 8, and 9 % nickel alloy steel plates for use in the water quenched and tempered condition intended for the fabrication of welded pressure vessels.

1.2 Material under this specification is available in three types having different chemical composition as follows:

1.3 Plates produced under this specification are subject to impact testing at -320°F [-195°C] for Type I or Type III, and -275°F [-170°C] for Type II; or at such other temperatures as are agreed upon.

1.4 The maximum thickness of plates is limited only by the capacity of the material to meet the specified mechanical property requirements; however, current mill practice normally limits this material to 2 in. [50 mm] max.

1.5 This material is susceptible to magnetization. Use of magnets in handling after heat treatment should be avoided if residual magnetism would be detrimental to subsequent fabrication or service.

1.6 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

2. Referenced Documents

2.1 ASTM Standards:

• A20/A20M Specification for General Requirements for Steel Plates for Pressure Vessels
• A435/A435M Specification for Straight-Beam Ultrasonic Examination of Steel Plates
• A577/A577M Specification for Ultrasonic Angle-Beam Examination of Steel Plates
• A578/A578M Specification for Straight-Beam Ultrasonic Examination of Rolled Steel Plates for Special Applications

3. General Requirements and Ordering Information

3.1 Material supplied to this material specification shall conform to Specification A20/A20M. These requirements outline the testing and retesting methods and procedures, permitted variations in dimensions, and mass, quality and repair of defects, marking, loading, and ordering information.

3.2 In addition to the basic requirements of this specification, certain supplementary requirements are available when additional control, testing, or examination is required to meet end use requirements. The purchaser is referred to the listed supplementary requirements in this specification and to the detailed requirements in Specification A20/A20M.

3.3 If the requirements of this specification are in conflict with the requirements of Specification A20/A20M, the requirements of this specification shall prevail.

4. Manufacture

4.1 Steelmaking Practice — The steel shall be killed and shall conform to the fine austenitic grain size requirement of Specification A20/A20M.

5. Heat Treatment

5.1 All plates shall be heat treated in accordance with 5.2. Shell plates and other parts, including heads and reinforcing pads, which are heated for forming, shall be heat treated after forming in accordance with 5.2.

5.2 Heat Treatment Procedure

Heat treat all plates by heating to a suitable temperature within the range from 1475 to 1700°F [800 to 925°C], holding for a sufficient time to obtain uniform temperature throughout the plate thickness and then quenching in water. Subsequently, temper the plates within the range from 1050 to 1175°F [565 to 635°C] for Type I and Type II, or from 1000 to 1125°F [540 to 615°C] for Type III, holding at this temperature for a minimum of 30 min per inch [1.2 min/mm] of thickness but not less than 15 min, and cool in air or water quench at a rate not less than 300°F/h [165°C/h].

5.2.1 Hardening

The plates shall be heated to a temperature within the range from 1475 to 1700°F [800 to 925°C], held at that temperature for a sufficient time to obtain uniform temperature throughout the plate thickness, and then quenched in a liquid media.

5.2.2 Tempering

The plates shall be tempered at a temperature within the range from 1050 to 1175°F [565 to 635°C] for Type I and Type II, or from 1000 to 1125°F [540 to 615°C] for Type III; being held at that temperature for a minimum of 30 min per inch [1.2 min/mm] of thickness, but in no case less than 15 min, and then cooled in air or liquid-quenched at a rate not less than 300°F/h [165°C/h].

5.2.2.1 Intermediate Heat Treatment (Optional)

Prior to the tempering treatment, the plates may be subjected to an intermediate heat treatment consisting of heating to a temperature in the range from 1165 to 1290°F [630 to 700°C] for Type I, or 1185 to 1310°F [640 to 710°C] for Type II, or 1205 to 1330°F [650 to 720°C] for Type III; holding at that temperature for a suitable time, but in no case less than 15 min, and then water-quenching to below 300°F [150°C] in the case of plate thicknesses of more than 5/8 in. [16 mm] or cooling in air or water-quenching to below 300°F [150°C] in the case of plate thicknesses of 5/8 in. [16 mm] and under.

Note: The intermediate heat treatment is for the purpose of enhancing elongation and notch-toughness and for reducing susceptibility to strain-aging embrittlement and temper embrittlement. It may be performed at the option of the material manufacturer or may be specified by the purchaser.

6. Chemical Requirements

6.1 The steel shall conform to the chemical requirements shown in Table 1 unless otherwise modified in accordance with Supplementary Requirement S17, Vacuum Carbon-Deoxidized Steel, in Specification A20/A20M.

7. Mechanical Requirements

7.1 Tension Test Requirements

7.1.1 The material as represented by tension-test specimens shall conform to the requirements specified in Table 2.

7.1.2 Upon agreement between the purchaser and the manufacturer, yield strength may be determined by the extension under load method, using 0.005 in./in. [0.005 mm/mm] total extension.

7.1.3 For nominal plate thicknesses of ¾ in. [20 mm] and under, the 1½ in. [40 mm] wide rectangular specimen may be used for the tension test and the elongation may be determined in a 2 in. [50 mm] gage length that includes the fracture and shows the greatest elongation.

7.2 Impact Test Requirements

7.2.1 Charpy V-notch impact tests shall be made in accordance with Specification A20/A20M.

7.2.2 The longitudinal axis of the test specimens shall be transverse to the final rolling direction of the plate.

7.2.3 Unless otherwise agreed, tests shall be conducted at -320°F [-195°C] for Type I or Type III, and at -275°F [-170°C] for Type II.

7.2.4 Each test specimen shall have a lateral expansion opposite the notch of not less than 0.015 in. [0.381 mm].

8. Finish

8.1 Because retained scale may mask surface imperfections, as well as mar the plate surface, plates shall be descaled by the producer after heat treatment. In the case of material to be heat-treated by the purchaser, the plates shall be descaled by the producer prior to shipment.

9. Marking

9.1 In addition to the marking required in Specification A20/A20M, each plate shall be legibly stamped or stenciled, depending upon the ordered thickness, with the letters QT, except as otherwise specified in 9.1.1.

9.1.1 When the optional heat treatment in 5.2.2.1 is performed, the plates shall be marked with the letters QTT instead of QT.

10. Keywords

10.1 alloy steel; alloy steel plate; pressure containing parts; pressure vessel steels; steel plates; steel plates for pressure vessel applications