Section 7 Forgings for boilers, pressure vessels and piping systems

7.1.1 Provision is made in this Section for carbon-manganese and low alloy steel forgings intended for use in the construction of boilers, pressure vessels and piping systems where the design temperature is not lower than 0°C.

7.1.2 In addition to specifying mechanical properties at ambient temperature for the purposes of acceptance testing, these requirements give details of appropriate mechanical properties at elevated temperatures to be used for design purposes.

7.1.3 Forgings used in the construction of equipment for the containment of liquefied gases are to comply with the requirements of Ch 5, 8 Ferritic steel forgings for low temperature service, except for those used in piping systems, where the design temperature is not lower than 0°C. Forgings for other pressure vessels and piping systems, where the use of steels with guaranteed impact properties at low temperatures is required, are also to comply with Ch 5, 8 Ferritic steel forgings for low temperature service.

7.2.1 The chemical composition of ladle samples is to comply with the appropriate requirements of Table 5.7.1 Chemical composition.

7.3.1 Carbon-manganese steel forgings are to be normalised, normalised and tempered or quenched and tempered.

7.3.2 Alloy steel forgings are to be normalised and tempered or quenched and tempered.

7.3.3 No forging is to be fully heat treated more than twice.

7.4.1 Except as provided in Ch 5, 7.4 Mechanical tests 7.4.2 and Ch 5, 7.4 Mechanical tests 7.4.4, at least one tensile test is to be taken from each forging and, where the dimensions and shape allow, the test specimen is to be cut in the longitudinal direction.

7.4.2 On seamless drums and headers which are initially forged with open ends, test material is to be provided at each end of each forging. Where forged with one solid end, test material is to be provided at the open end only. Except where the ends are to be subsequently closed by forging, the test material is not to be removed until heat treatment has been completed. Where the ends are to be closed, rings of test material are to be cut off prior to the closing operation and are to be heat treated with the finished forging. In all cases, the test specimens are to be cut in the circumferential direction.

7.4.3 Unless otherwise agreed, tensile test specimens are to be taken with their axis at approximately 12,5 mm below the surface of the forging.

7.4.4 Small forgings may be batch tested in accordance with Ch 5, 1.6 Test material 1.6.4 provided that hardness tests are carried out on each forging. In such cases, the mass of each forging is not to exceed 1 tonne and that of the batch is not to exceed 10 tonnes and the hardness values are to accord with Table 5.7.2 Mechanical properties for acceptance purposes.

7.4.5 If required by the Surveyors or by the Fabricators, test material may be given a simulated stress relieving heat treatment prior to the preparation of the test specimens. This has to be stated on the order, together with agreed details of the simulated heat treatment and the mechanical properties which can be expected.

7.4.6 Except as provided in Ch 5, 7.4 Mechanical tests 7.4.7, the results of all tensile tests are to comply with the requirements given in Table 5.7.2 Mechanical properties for acceptance purposes appropriate to the specified minimum tensile strength.

7.4.7 Where tests are taken at a depth greater than 12,5 mm from the surface or where they are taken in a transverse direction, the mechanical properties which can be expected are to be agreed.

7.4.8 On seamless drums and headers where tests are taken from each end, the variation in tensile strength is not to exceed 70 N/mm².

7.4.9 For small batch-tested forgings, the hardness values are to comply with the requirements of Table 5.7.2 Mechanical properties for acceptance purposes appropriate to the specified minimum tensile strength. If forgings of more than one thickness are to be supplied from one cast, then the test is to be made on the thickest forging.

7.5.1 Non-destructive testing is to be carried out in accordance with the requirements of the approved forging drawing and specification, or as otherwise agreed between the manufacturer, purchaser and Surveyor.

7.6.1 Where applicable, pressure tests are to be carried out in accordance with the requirements of the relevant Rules.

7.7.1 Nominal values for the minimum lower yield or 0,2 per cent proof stress at temperatures of 50°C and higher are given in Table 5.7.3 Mechanical properties for design purposes. These values are intended for design purposes only, and verification is not required except for materials complying with National or proprietary specifications where the elevated temperature properties used for design purposes are higher than those given in Table 5.7.3 Mechanical properties for design purposes.

Table 5.7.2 Mechanical properties for acceptance purposes

Type of steel	Diameter or equivalent thickness	Yield stress N/mm2	Tensile strength N/mm2	Elongation on % minimum	Hardness Brinell
Carbon-manganese not specifically fine grained	≤100	215	410 – 530	20	110 – 155
	>100 ≤500	205
	≤100	245	460 – 580	18	130 – 170
	>100	235
	≤100	265	490 – 610	16	140 – 180
	>100	255
Carbon-manganese, fine grained	≤100	235	410 – 530	20	110 – 155
	>100 ≤250	220
	≤100	275	460 – 580	18	130 – 170
	>100 ≤250	255
	≤100	305	490 – 610	16	140 – 180
	>100 ≤250	280
Alloy steel
1Cr 1/2Mo	—	275	440 – 590	19	110 – 160
2 1/4Cr1Mo	—	275	490 – 640	18	140 – 185

7.7.2 Where verification is required, at least one tensile test at the proposed design or other agreed temperature is to be made on each forging or each batch of forgings. The test specimen is to be taken from material adjacent to that used for tests at ambient temperature, and the test procedure is to be in accordance with the requirements of Ch 2 Testing Procedures for Metallic Materials. The results of all tests are to comply with the requirements of the National or proprietary specification.

7.7.3 Values for the estimated average stress to rupture in 100 000 hours are given in Table 5.7.4 Mechanical properties for design purposes: estimated average values for stress to rupture in 100 000 hours (units N/mm²) and may be used for design purposes.