Section 5 Stainless steel pressure pipes

5.1.1 Provision is made in this Section for austenitic and duplex stainless steel pipes suitable for the construction of piping systems for ships.

5.1.2 Austenitic stainless steels forgings are suitable for applications where the design temperature is not lower than -165°C.

5.1.3 Austenitic stainless steels may be suitable for service at elevated temperatures. Where such applications are proposed, details of the chemical composition, heat treatment and mechanical properties are to be submitted for consideration and approval.

5.1.4 Duplex stainless steels are suitable for applications where the design temperature is not lower than -20°C.

5.2.1 Pipes are to be manufactured by a seamless or a continuous automatic electric fusion welding process.

5.2.2 Welding is to be in a longitudinal direction, with or without the addition of filler metal.

5.2.3 The chemical composition of the ladle samples is to comply with the appropriate requirements of Table 6.5.1 Chemical composition.

5.3.1 Pipes are generally to be supplied by the manufacturer in the solution treated condition over their full length.

5.3.2 Alternatively, seamless pipes may be direct quenched immediately after hot forming, while the temperature of the pipes is not less than the specified minimum solution treatment temperature.

5.4.1 All pipes are to be presented in batches as defined in Ch 6, 1 General requirements for Class I and II piping systems.

5.4.2 Each pipe selected for test is to be subjected to tensile and flattening or bend tests and, where the wall thickness is 6 mm or greater, Charpy impact tests shall be performed at the test temperatures specified in Table 6.5.2 Mechanical properties for acceptance purposes.

5.4.3 The results of all mechanical tests are to comply with the appropriate requirements given in Table 6.5.2 Mechanical properties for acceptance purposes.

5.5.1  For materials used for piping systems for chemicals, corrosion tests are to be carried out on one per cent of the number of pipes in each batch, with a minimum of one pipe. For austenitic stainless steels this should be an intercrystalline corrosion test (see Ch 2, 9.1 Intergranular corrosion test) and for duplex stainless steels this should be a pitting corrosion test (see Ch 2, 9.2 Pitting corrosion test ). For the latter, the test temperatures shall be 20°C for S31803 and 30°C for S32750.

5.5.2 For pipes with an outside diameter not exceeding 40 mm, the test specimens are to consist of a full cross-section. For larger pipes, the test specimens are to be cut as circumferential strips of full wall thickness and having a width of not less than 12,5 mm. In both cases, the total surface area is to be between 15 and 35 cm².

5.5.3 Unless otherwise agreed or required for a particular chemical cargo, the testing procedure is to be in accordance with Ch 2, 9 Corrosion tests for austenitic stainless steels and Ch 12, 3.3 Duplex stainless steels 3.3.3.(c) for duplex stainless steels.

5.5.4 After immersion, the full cross-section test specimens are to be subjected to a flattening test in accordance with the requirements of Ch 2 Testing Procedures for Metallic Materials. The strip test specimens are to be subjected to a bend test through 90° over a mandrel of diameter equal to twice the thickness of the test specimen.

5.6.1 Fabricated pipework is to be produced from material manufactured in accordance with Ch 6, 5.2 Manufacture and chemical composition, Ch 6, 5.3 Heat treatment, Ch 6, 5.4 Mechanical tests and Ch 6, 5.5 Corrosion tests.

5.6.2 Welding is to be carried out in accordance with an approved and qualified procedure by suitably qualified welders.

5.6.3 Fabricated pipework may be supplied in the as-welded condition without subsequent solution treatment provided that welding procedure tests have demonstrated satisfactory material properties including resistance to intercrystalline corrosion (austenitic stainless steel) or pitting corrosion (duplex stainless steel).

5.6.4 In addition, butt welds are to be subjected to 5 per cent radiographic examination for Class I, and 2 per cent for Class II pipes.

5.6.5 Fabricated pipework in the as-welded condition and intended for systems located on deck is to be protected by a suitable corrosion control coating.

5.7.1 Each test certificate is to be of the type and give the information detailed in Ch 1, 3.1 General together with general details of heat treatment and, where applicable, the results obtained from the appropriate corrosion tests. As a minimum, the chemical composition is to include the content of all the elements detailed in Table 6.5.1 Chemical composition.