Section 4 Ferritic steel pressure pipes for low temperature service

4.1.1 Provision is made in this Section for carbon, carbon-manganese and nickel pipes intended for use in the piping arrangements for liquefied gases where the design temperature is less than 0°C. These requirements are also applicable for other types of pressure piping systems where the use of steels with guaranteed impact properties at low temperatures is required.

4.2.1 Carbon and carbon-manganese steel pipes are to be manufactured by a seamless, electric resistance or induction welding process.

4.2.2 Nickel steel pipes are to be manufactured by a seamless process.

4.2.3 Seamless pipes may be hot finished or cold finished. Welded pipes may be as-welded, hot finished or cold finished. The terms `hot finished', `cold finished' and `as-welded' apply to the condition of the pipes before final heat treatment.

4.2.4 The method of deoxidation and the chemical composition of ladle samples are to comply with the appropriate requirements given in Table 6.4.1 Chemical composition.

4.3.1 Pipes are to be supplied in the condition given in Table 6.4.3 Heat treatment.

4.4.1 All pipes are to be presented for test in batches as defined in Ch 6, 1 General requirements for Class 1 pressure piping systems, but in addition the material in each batch is to be from the same cast.

4.4.2 At least two per cent of the number of lengths in each batch is to be selected at random for the preparation of tests.

4.4.3 Each pressure pipe selected for test is to be subjected to tensile, flattening or bend test at room temperature and, where the wall thickness is 6 mm or greater, an impact test at the test temperature specified in Table 6.4.2 Mechanical properties for acceptance purposes.

4.4.4 The impact tests are to consist of a set of three Charpy V-notch test specimens cut in the longitudinal direction with the notch perpendicular to the original surface of the pipe. The dimensions of the test specimens are to be in accordance with the requirements of Ch 2 Testing Procedures for Metallic Materials.

4.4.5 The results of all tensile, impact (when applicable), flattening and bend tests are to comply with the appropriate values in Table 6.4.2 Mechanical properties for acceptance purposes. See Ch 2, 1.4 Re-testing procedures for re-testing procedures.

Table 6.4.1 Chemical composition

Type of steel	Grade	Method of deoxidation	Chemical composition of ladle sample %
			C max.	Si	Mn	P max.	S max.	Ni	Alsol see Note	Residual elements
Carbon	360	Fully killed	0,17	0,10—0,35	0,40—1,00	0,030	0,025	—	0,015 min.	Cr	0,25
										Cu	0,30
										Mo	0,10
										Ni	0,30
Carbon- manganese	410 and 460		0,20	0,10—0,35	0,60—1,40	0,030	0,025	—	0,015 min.	Total	0,70
3 Ni	440		0,15	0,15—0,35	0,30—0,90	0,025	0,020	3,25—3,75	—	Cr	0,25
										Cu	0,30
										Mo	0,10
9Ni	690		0,13	0,15—0,30	0,30—0,90	0,025	0,020	8,50—9,50	—	Total	0,60
Note Where a minimum Alsol of 0,015% is specified, the determination of the total aluminium is acceptable provided that the result is not less than 0,020%.

Table 6.4.2 Mechanical properties for acceptance purposes

Type of steel	Grade	Yield stress N/mm2	Tensile strength N/mm2	Elongation on 5,65% minimum	Flattening test constant C	Bend test diameter of former (t = thickness)	Charpy V-notch impact tests
							Test temperature °C	Average energy J minimum
Carbon	360	210	360—480	24	0,10	4t	-60 (see Note)	27
Carbon- manganese	410	235	410—530	22	0,08	4t		27
	460	260	460—580	21	0,07
3½Ni	440	245	440—590	16	0,08	4t	–95	34
9Ni	690	510	690—840	15	0,08	4t	–196	41
Note The test temperature for carbon-manganese steels may be 5°C below the design temperature if the latter is above -55°C, with a maximum test temperature of -20°C.