1. Scope

1.1 This specification covers double-normalized and tempered 9 % nickel steel plates intended particularly for welded pressure vessels for cryogenic service.

1.2 Plates produced under this specification are subject to impact testing at -320°F [-195°C] or at such other temperatures as are agreed upon.

1.3 The maximum thickness of plates is limited only by the capacity of the material to meet the specific mechanical property requirements.

1.4 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.

1.5 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.

1.6 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 that are heated for forming shall be heat treated after forming in accordance with 5.2.

5.2 Heat Treatment Procedure:

5.2.1 First Normalizing Treatment

Heat the plate to a uniform temperature of 1650 ± 25°F [900 ± 15°C], hold at that temperature for a minimum of 1 h/in. [2.4 min/mm] of thickness, but in no case less than 15 min, and cool in air.

5.2.2 Second Normalizing Treatment

Reheat the plate to a uniform temperature of 1450 ± 25°F [790 ± 15°C], hold at that temperature for a minimum of 1 h/in. [2.4 min/mm] of thickness, but in no case less than 15 min, and cool in air.

5.2.3 Tempering Treatment

Reheat the plate to a uniform temperature within the range from 1050 to 1125°F [565 to 605°C], hold within that temperature range for a minimum of 1 h/in. [2.4 min/mm] of thickness, but in no case less than 15 min, and cool in air or water quench at a rate not less than 300°F/h [165°C/h].

5.2.4 Hot Forming Consideration

If hot forming is performed after heating to a temperature within the range from 1650 to 1750°F [900 to 955°C] the first normalizing treatment (5.2.1) may be omitted.

5.2.5 Fabricator Responsibility

When the plates are heat treated by the fabricator, it shall be the fabricator's responsibility to apply the proper heat treatment and conduct tests it deems necessary to ensure that the specified properties are attained.

6. Chemical Requirements

6.1 The steel shall conform to the chemical composition 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

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

7.1.1 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.

7.1.2 For nominal plate thicknesses of ¾ in. [20 mm] and under, the ½-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.

7.1.3 One tension test shall be taken from each plate as heat treated.

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].

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. Keywords

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