Section 4 Steels for boilers and pressure vessels

4.1.1 Provision is made in this Section for carbon, carbon-manganese and alloy steels intended for use in the construction of boilers and pressure vessels. In addition to specifying mechanical properties at ambient temperature for the purposes of acceptance testing, these requirements also give details of appropriate mechanical properties at elevated temperatures which may be used for design purposes.

4.1.2 Where it is proposed to use a carbon or carbon-manganese steel with a specified minimum tensile strength intermediate to those given in this Section, corresponding minimum values for the yield stress, elongation and mechanical properties at elevated temperatures may be obtained by interpolation.

4.1.3 Carbon and carbon-manganese steels with a specified minimum tensile strength of greater than 490 N/mm² but not exceeding 520 N/mm² may be accepted, provided that details of the proposed specification are submitted for approval.

4.1.4 Where it is proposed to use alloy steels other than as given in this Section, details of the specification are to be submitted for approval. In such cases the specified minimum tensile strength is not to exceed 600 N/mm².

4.1.5 Materials intended for use in the construction of the cargo tanks and process pressure vessels storage tanks for liquefied gases and for other low temperature applications are to comply with the requirements of Ch 3, 6 Carbon–manganese and nickel alloy steels for low temperature service or Ch 3, 7 Austenitic and duplex stainless steels, as appropriate.

4.2.1 The method of deoxidation and the chemical composition of ladle samples are to comply with the appropriate requirements of Table 3.4.1 Chemical composition and deoxidation practice.

4.2.2 For plate supplied from coil, the chemical analysis may be transposed from the certificate of the coil manufacture onto the re-processor’s certificate.

4.3.1 All materials are to be supplied in a condition complying with the requirements given in Table 3.4.2 Condition of supply except that, when agreed, material intended for hot forming may be supplied in the as-rolled condition.

4.4.1 For plates, a tensile test specimen is to be taken from one end of each piece when the mass does not exceed 5 tonnes and the length does not exceed 15 m. When either of these limits is exceeded, tensile test specimens are to be taken from both ends of each piece. A piece is to be regarded as the rolled product from a single slab or from a single ingot if this is rolled directly into plates.

4.4.2 For strip, tensile test specimens are to be taken from both ends of each coil.

4.4.3 Sections and bars are to be presented for acceptance test in batches containing not more than 50 lengths, as supplied. The material in each batch is to be of the same section size, from the same cast and in the same condition of supply. One tensile test specimen is to be taken from material representative of each batch, except that additional tests are to be taken when the mass of a batch exceeds 10 tonnes.

4.4.4 Where plates are required for hot forming and it has been agreed that the heat treatment will be carried out by the fabricator, the tests at the steelworks are to be made on material which has been cut from the plates and given a normalising and tempering heat treatment in a manner simulating the treatment which will be applied to the plates.

4.4.5 If required by the Surveyors or by the fabricator, 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 accepted.

4.4.6 The results of all tensile tests are to comply with the appropriate requirements given in Table 3.4.3 Mechanical properties for acceptance purposes: carbon and carbon-manganese steels - As-rolled to Table 3.4.5 Mechanical properties for acceptance purposes: alloy steels - Normalised and tempered.

Table 3.4.4 Mechanical properties for acceptance purposes: carbon and carbon-manganese steels - Normalised or normalised rolled

Grade of steel	Thickness mm (see Note)	Yield stress N/mm2 minimum	Tensile strength N/mm2	Elongation on 5,65 % minimum
360	>3≤16	205	360 – 480	26
	>16≤40	195		26
	>40≤63	185		25
410	>3≤16	235	410 – 530	24
	>16≤40	225		24
	>40≤63	215		23
460	>3≤16	285	460 – 580	22
	>16≤40	255		22
	>40≤63	245		21
490	>3≤16	305	490 – 610	21
	>16≤40	275		21
	>40≤63	265		20
360 FG	>3≤16	235	360 – 480	26
	>16≤40	215		26
	>40≤63	195		25
410 FG	>3≤16	265	410 – 530	24
	>16≤40	245		24
	>40≤63	235		23
460 FG	>3≤16	295	460 – 580	22
	>16≤40	285		22
	>40≤63	275		21
490 FG	>3≤16	315	490 – 610	21
	>16≤40	315		21
	>40≤63	305		21
510 FG	>3≤16	355	510 – 650	21
	>16≤40	345
	>40≤63	335
Note For thicknesses greater than 63 mm, the minimum values for yield stress may be reduced by 1% for each 5 mm increment in thickness over 63 mm. The minimum elongation values may also be reduced one unit, for all thicknesses over 63 mm. For thicknesses over 100 mm, the above values are to be agreed.

4.4.7 Where plate is supplied from coil, the tensile tests are to be taken from the de-coiled plate in accordance with the frequency specified for the Grade as required by this Section.

Table 3.4.5 Mechanical properties for acceptance purposes: alloy steels - Normalised and tempered

Grade of steel	Thickness mm (see Note)	Yield stress N/mm2 minimum	Tensile strength N/mm2	Elongation on 5,65 % minimum
13Cr Mo45	≤63	305	470-620	20
11Cr Mo910	≤16	275	480-630	18
11Cr Mo910	>16≤63	265	480-630	18
Note For thicknesses greater than 63 mm, the minimum values for yield stress may be reduced by 1% for each 5 mm increment in thickness over 63 mm. The minimum elongation values may also be reduced one unit, e.g. for all thicknesses over 63 mm. For thicknesses over 100 mm, the above values are to be agreed.

4.4.8 All test specimens are to be taken in the transverse direction unless otherwise agreed.

4.4.9 When material will be subject to strains in a through thickness direction, it is recommended that it should have specified through thickness properties in accordance with the requirements of Ch 3, 8 Plates with specified through thickness properties.

4.5.1 The particulars detailed in Ch 3, 1.12 Identification of materials are to be marked on all materials which have been accepted.

4.6.1 At least two copies of each test certificate are to be provided. They are to be of the type and to give the information detailed in Ch 3, 1.13 Certification of materials and, additionally, are to state the specified maximum carbon equivalent. As a minimum, chemical composition is to include the content of any grain refining elements used and of the residual elements, as detailed in Table 3.4.1 Chemical composition and deoxidation practice.

4.7.1 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 3.4.6 Mechanical properties for design purposes (see 4.7.1) : carbon and carbon-manganese steels - As-rolled to Table 3.4.8 Mechanical properties for design purposes (see 4.7.1): alloy steels - Normalised and tempered .

4.7.2 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 given in Table 3.4.6 Mechanical properties for design purposes (see 4.7.1) : carbon and carbon-manganese steels - As-rolled to Table 3.4.8 Mechanical properties for design purposes (see 4.7.1): alloy steels - Normalised and tempered .

4.7.3 In such cases, at least one tensile test at the proposed design or other agreed temperature is to be made on material from each cast. Where materials of more than one thickness are supplied from one cast, the thickest material is to be tested. The test specimens are to be prepared from material adjacent to that used for tests at ambient temperature. The axis of the test specimens is to be between mid and quarter thickness of the material and the test specimens are to be machined to dimensions in accordance with the requirements of Ch 2 Testing Procedures for Metallic Materials. The test procedure is also to be as detailed in Ch 2 Testing Procedures for Metallic Materials, and the results are to comply with the requirements of the National or proprietary specifications.

4.7.4 As an alternative to Ch 3, 4.7 Mechanical properties for design purposes 4.7.3, a manufacturer may carry out an agreed comprehensive test program for a stated grade of steel to demonstrate that the specified minimum mechanical properties at elevated temperatures can be consistently obtained. This test program is to be carried out under supervision of the Surveyors, and the results submitted for assessment and approval. When a manufacturer is approved on this basis, tensile tests at elevated temperatures are not required for acceptance purposes but, at the discretion of the Surveyors, occasional check tests of this type may be requested.

4.7.5 Values for the estimated average stress to rupture in 100 000 hours are given in Table 3.4.9 Mechanical properties for design purposes (see 4.7.5): estimated average values for stress to rupture in 100 000 hours (units N/mm²) and may be used for design purposes.