20 #(Grade 20) seamless steel pipe
 
 
1. product introduction
20 # seamless steel pipe is widely used in petrochemical and other industries for its excellent performance and suitable price. 20 #. There are national standards such as seamless steel tubes for fluid transportation (GB / t8163-2008), seamless steel tubes for low and medium pressure boilers (gb3087-2008), seamless steel tubes for petroleum cracking (gb9948-2013) and seamless steel tubes for high pressure fertilizer equipment (gb6479-2013).
 
There are great differences in price and effect of 20 # seamless steel pipes of different standards. At present, the price of 20 # seamless steel pipes manufactured according to GB 6479-2013 is about 1000 yuan / ton higher than that manufactured according to GB / T 8163-2008.
 
 
What are the standards for 20 # seamless steel pipes?
 (1) GB / t8163-2008 seamless steel pipe for fluid transportation
 (2) gb3087-2008 seamless steel tubes for low and medium pressure boilers
 (3) seamless steel tubes for petroleum cracking (GB / T 9948-2013)
 (4) seamless pipe for high pressure fertilizer equipment (GB / T 6479-2013)
 (5) GB / T 5310-2017 seamless steel tubes for high pressure boilers (in the standard, the steel number is 20g; G refers to boiler steel tubes)
 
 
2. 20 # chemical composition
Table 1, Chemical Composition of 20 # Seamless Steel Pipe
 

Standard	Chemical composition
	C	Si	Mn	Cr	Mo	Ni	Cu	V	P	S
				≤
GB/T8163	0.17-0.23	0.17-0.37	0.35-0.65	0.25	--	0.30	0.25	--	0.035	0.035
GB/T 9948					0.15	0.25	0.20	0.08	0.025	0.015
GB/T 6479

 
It can be seen from table 1 that the content of main elements (such as C, Si, Mn) in the chemical composition of 20 × seamless steel pipe in each material standard is the same. The content of residual elements (such as Ni, CI, Cu, Mo, V) in steel in gb9948-2013 and GB 6479-2013 are the same, but there are slight differences between GB / T 8163-2008 and the above two standards. The main difference of chemical composition lies in the content of P and s.
 
 
3. 20 # mechanical properties (mechanical properties)
Table 2, Mechanical Properties of 20 # Seamless Steel Pipe
 

Standard	Mechanical Properties
	Tensile strength/MPa	Yield strength/MPa			Elongation		KV2/J
		S≤16mm	16-30mm	＞30mm	Portrait	Transverse	Portrait	Transverse
		≥					Test temperature/℃  0℃
GB/T8163	410-530	245	235	225	20		---
GB/T 9948	410-550	245			24	22	≥40	≥27
GB/T 6479	410-550	245	16-40mm	＞40mm	24	22	≥40	≥27
			235	225

It can be seen from table 2 that the tensile properties of 20 # seamless steel pipes in each material standard are basically the same, and the main difference is impact test.
 The 20 # seamless steel pipe manufactured in accordance with GB / t8163-2008 shall not be subject to impact test. Charpy V-notch impact test shall be carried out only when required by the demander, negotiated by the supplier and the demander, and specified in the contract.
 
For 20 # seamless steel pipes manufactured according to GB 9948-2013, room temperature impact test shall be conducted only for steel pipes with an external diameter of not less than 76mm and a wall thickness of not less than 14mm. Impact test for other steel pipes shall be negotiated by both parties and agreed in the contract.
 
For 20 # seamless steel pipes manufactured according to GB 6479-2013, the steel pipes with D ≥ 76mm and s ≥ 6.5mm shall be subject to 0 ℃ impact test.
 
Obviously, the requirements of mechanical properties of 20 # seamless steel pipe manufactured according to GB 6479-2013 are higher and stricter than those of other two standards.
 
 
4. 20 # material substitution
In the procurement stage or on-site construction process, the construction unit often raises the issue of material substitution to the design unit. In addition to the requirements for alternative use due to different pipe specifications, when steel pipes produced according to other standards are used instead, the designer shall pay attention to the differences between design conditions and standards so as to correctly sign for confirmation.
 
A) under the premise of the same specification, the 20 # seamless steel pipe produced according to the standards of GB 6479-2013 and GB 9948-2013 can replace the 20 # seamless steel pipe produced according to the standards of GB 3087-2008 and GB / T 8163-2008.
 
B) as the 20 # seamless steel pipe produced in accordance with GB 6479-2013 and GB 9948-2013 has excellent toughness, it is recommended to use the 20 # seamless steel pipe produced in accordance with GB 6479-2013 and GB 9948-2013 for the steel pipe at low temperature not lower than - 20 ℃.
 
C) the 20 # seamless steel pipe produced in accordance with GB / T 8163-2008 only uses fluid. Because the requirements of GB 3087-2008 standard are higher than that of GB / T 8163-2008 standard in terms of allowable wall thickness difference, bending test, low power inspection and surface quality, in addition, GB 3087-2008 standard also specifies the high temperature strength requirements, so under the condition that the maximum test pressure is not greater than lompa, the 20 # seamless steel pipe produced according to GB 3087-2008 standard can replace the 20 # seamless steel pipe produced according to GB / T 8163-2008 standard. Steel pipe. When the wall thickness of steel pipe is ≥ 15mm, pay attention to calculate the wall thickness of steel pipe when replacing.