Gr. 6 seamless steel pipe for low temperature

Abstract Base on ASTM A 333 /A333m standaid and user requirements he G r 6 level low tmperauiee seam less steel tube was developed and produced-
Keywords low tempeiauiie ; seam less steel tube ; perfomance

Low-temperature seamless steel pipes are mainly used in ultra-low temperature cold storage, pipelines and pipe parts for transporting ultra-low temperature liquefied gas , Its production and acceptance adopt the standard STAM A 333/ A 33 M of the American Society for Materials . Seamless steel pipes for low temperature require good mechanical properties , process properties and low temperature impact properties . In order to broaden the product structure of Guangzhou Iron and Steel Seamless Steel Tube Factory ( hereinafter referred to as the seamless factory ) , improve market competitiveness , Through in-depth research on ASTM A 333 A 333 M standards, combined with user requirements , Utilize the existing equipment and process conditions of the seamless factory to trial-manufacture and trial-produce seamless steel pipes for low temperature for users .
1 Comparative Analysis of Standard Requirements
1 . 1 chemical composition

• 1 for the chemical composition requirements of STAM A 333/ A 333 M Gr 6 Grade "Seamless Steel Tubes for Low Temperature " .
• Note : When the carbon content is lower than 0.30 % , the manganese content can be at 1.06 % for every reduction of 0.01 % . The above increases by 0.05 %, until the maximum permissible manganese content is 1.35 % .
• The steel grades currently used by the seamless factory are: 10 , 20 , 45 ,

20CMo > 30CiMo < Q345 etc. The grade with chemical composition close to Gr 6 steel grade is Q345, and its chemical composition requirements are shown in Table 2
Table 2 Q345 chemical composition %

C	Mn	P	S	Si	V	Nb	Ti
<0 20	1.00-1.60	<0 040	<0 040	<0 55	-	-	-

Since the carbon content of Q345 is not more than 0.020 %, the manganese content is 100 % ~ 160 %, and the sulfur and phosphorus contents are not more than 0.040 % . In the case of controlling the content of carbon, manganese, sulfur and phosphorus, it can be replaced by Q345 . Therefore, the material can be selected from the Q345 grade to organize production by selecting a furnace number with a carbon content of 0.16 % to 0.20% , a manganese content of 1.30% to 1.35% , and a phosphorus and sulfur content of not more than 0.025% .
1 2 Mechanical properties
(1) STAM A 333/ A 333 M Gr 6 " Seamless Steel Tubes for Low Temperature Use " standard , the requirements for tensile properties are : the longitudinal tensile properties of steel tubes delivered under heat treatment ( annealing or normalizing ) should meet the requirements .

(2) According to GB/T8163-2008 " Seamless Steel Tubes for Conveying Fluids " , the longitudinal tensile properties of Q345 steel tubes delivered under heat treatment ( annealing or normalizing ) should meet the requirements in Table 4 .

Table 4 Mechanical properties of Q345 steel pipe
level	Longitudinal Tensile Properties
	Tensile strength RmMPa Yield strength Re ] MPa Elongation after fracture A %
Q 345	$470 ~ 630	$240 $20
1 3	Impact test

1 ) STAM A333/A333M Gr 6 Grade "Seamless steel pipe for low temperature use: Standard, Gr 6 grade steel pipes are subjected to impact tests at -45C .
(2) GB / T 8163-2008 " Seamless steel pipes for conveying fluids " standard, the minimum impact test temperature of Q345 steel pipes is -40C .
Q345B steel produced by Hunan Iron and Steel Co. , Ltd. and the tube billet with furnace number 09105580 were selected , and the composition analysis was carried out . The results are shown in Table 5 .
Table 5 Chemical Composition % of Q345B Tube Billet of Xiangshan Iron and Steel

Grade	C	Mn	P	S	Si	V	Mo	As
Q 345 B	0 . 16	1 . 34	0 . 013	0 . 002	0 . 31	0 . 001	0 . 001	0 . 005

2 steel pipe trial production
2- 1 Production process route
The production process route is as follows :
Tube blank 1 ► heating f piercing 1 ► rolling pipe f head 1 ► cooling head cold drawing v— pickling ◄ — weighing ◄ — inspection and batch annealing f finishing— ►inspection— ►flaw detection , spray inspection and storage
Table 8 Mechanical and process performance test results of finished pipe

serial number	Specification /nm	Rm / MPa	Re l / MPa	A /%	V -shaped impact energy /j・cm 2	Flattening test
1	48 3X3 7X6100	605/645	460/550	27/26	34/31/27	qualified
2	42 2X3 6X6100	540/560	400/410	31 5/31 5	33/33/30	qualified
3	33 3X3 4X6100	545/565	360/370	32 5/27	33/31/28	-
4	26 7X2 9X6100	565/560	395/400	33/30 5	9/9/8	-
5	21 3X2 8X6100	560/555	420/410	37/37	6/6/5	-
6	10 3X2 4X6100	510/505	345/350	31/31	5/4/4	-

The impact test samples numbered 4, 5, and 6 in the table are non-standard sizes (5. 0X1. 4X55, 5. 0X1. 9X55, 5. 0X2. 4X55), and the test results are for reference only.

The above inspection results show that the chemical composition , mechanical properties , process properties and heat treatment system of the trial-produced steel pipes are all in line with ASTM A 333 Gr 6 grade steel pipe standards and user requirements .

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