Low temperature steel pipe is medium carbon structural steel, cold and hot plus low temperature steel pipe can be good, good mechanical properties, and low price, wide source, so it is widely used. Its biggest weakness is low hardenability, large section size and relatively high requirements of the workpiece should not be used.
Brief introduction
Low temperature steel pipes are used in industries where extremely cold conditions are present, such as oil and gas production, refrigeration systems, and cryogenic applications.
Low temperature steel pipes are generally made of carbon steel or alloyed steel and have a higher nickel content to improve their resistance to low-temperature embrittlement.
The most commonly used grades for low temperature steel pipes are ASTM A333 Grade 6 and ASTM A420 Grade WPL6. These materials offer good strength and toughness, even at very low temperatures.
Low temperature steel pipes are subject to specific requirements for impact testing and stress relaxation at low temperatures. This is to ensure that the pipes can withstand the stresses and strains induced by cold temperatures without fracturing or suffering from brittle failure.
In summary, low temperature steel pipes are specialized pipes designed to operate in extremely cold conditions, and they are made of materials that can withstand the stresses and strains induced by low temperatures without fracturing or suffering from brittle failure.
Seamless steel pipes for cryogenic piping
Spot specification:8-1240×1-200mm<1/8″-48″×SCH5S-SCH160,STD,XS,XXS>
product material:10MnDG,09DG,09Mn2VDG,06Ni3MoDG,ASTM A333-Grade1,Grade3,Grade4,Grade6,Grade7,Grade8,Grade9,Grade10,Grade11
Application: It is suitable for seamless steel pipes of -45℃~-195℃ cryogenic pressure vessel pipes and cryogenic heat exchanger pipes
Production process: cold drawing and hot rolling
Weight calculation formula :(outer diameter – wall thickness)* wall thickness *0.02466/1000= m/ton
Heat treating regime
| Low temperature steel pipe standard | material mark | Heat treatment system of cryogenic steel tubes | Mechanical properties of cryogenic steel tubes | ||||||
| σb /MPa | σs /MPa≥ | δ5 /%≥ | HB | HC | impulse test | ||||
| /°C | /J≥ | ||||||||
| GB6479 | 10 | normalizing | 335~490 | 205 | 24 | — | — | -20 | 18 |
| GB6479 | 20 | normalizing | 410~550 | 245 | 24 | — | — | -20 | 18 |
| GB6479 | 16Mn | normalizing | 490~670 | 320 | 21 | — | — | -40 | 21 |
| GB5310 | 20G | Normalizing, hot rolled pipe temperature is not less than 900°C can replace normalizing | 410~550 | 245 | 24 | — | — | -20 | 18 |
| GB150-1998 · Appendix A-A3 | 09MnD | normalizing | 400~540 | 240 | 26 | — | — | -50 Documents’10×10 7.5×10 5×10 | — 21 18 14 |
| GB13296 GB/T14976 | All austenitic stainless steel seamless and welded tubes | — | — | — | — | — | — | -196 | 18 |
| Standard number and main purpose | Low temperature steel pipe | Heat treatment system of cryogenic steel tubes | thickness/mm | Tensile test of cryogenic steel tubes | impulse test | hardness | ||||
| σb /MPa | σs /MPa ≥ | δ5 /% ≥ | Φ /% ≥ | temperature /°C | Akv /J ≥ | HB≤ | ||||
| ASME Seamless and welded nominal tubes for low temperature | SA333Gr.1 | ≥845°C Normalizing, air cooling | — | ≥380 | 205 | 35 | — | -45 | 18 | — |
| SA333Gr.3 | ≥845°C Normalizing, air cooling | — | ≥450 | 240 | 30 | — | -100 | 18 | — | |
| SA333Gr.6 | ≥845°C Normalizing, air cooling | — | ≥415 | 240 | 30 | — | -45 | 18 | — | |
| SA333Gr.7 | ≥845°C Normalizing, air cooling | — | ≥450 | 240 | 30 | — | -75 | 18 | — | |
| SA333Gr.8 | First time : Normalizing, air cooling:quench(800°C±15°C)+temper(565~605°C) Second Time :(900°C±15°C)air cooling+(790°C±15°C)air cooling+(565~605°C)air cooling or water quenching | — | ≥690 | 515 | 22 | — | -195 | — | — | |
| SA333Gr.9 | ≥845°C Normalizing, air cooling | — | ≥435 | 315 | 28 | — | -75 | 18 | — | |
| ASME Carbon steel and alloy steel tubes, seamless and welded, for low temperature use | SA333Gr.1 | ≥845°C Normalizing, air cooling | — | 380≥ | 205 | 35 | — | -45 | 18 | — |
| SA333Gr.3 | ≥845°C Normalizing, air cooling | — | ≥450 | 240 | 30 | — | -100 | 18 | — | |
| SA333Gr.6 | ≥845°C Normalizing, air cooling | — | ≥415 | 240 | 30 | — | -45 | 18 | — | |
| SA333Gr.7 | ≥845°C Normalizing, air cooling | — | ≥450 | 240 | 30 | — | -75 | 18 | — | |
| SA333Gr.8 | First time : Normalizing, air cooling:quench(800°C±15°C)+temper(565~605°C) Second Time :(900°C±15°C)air cooling+(790°C±15°C)air cooling+(565~605°C)air cooling or water quenching | — | ≥690 | 520 | 22 | — | -195 | 18 | — | |
Impact temperature:
| Grade | Minimum impact test temperature | |
| ℉ | ℃ | |
| 16MnDG | — | -45 |
| 10MnDG | — | -45 |
| 09DG | — | -45 |
| 09Mn2VDG | — | -70 |
| 06Ni3MoDG | — | -100 |
| A333 Grade1 | -50 | -45 |
| A333 Grade3 | -150 | -100 |
| A333 Grade4 | -150 | -100 |
| A333 Grade6 | -50 | -45 |
| A333 Grade7 | -100 | -75 |
| A333 Grade8 | -320 | -195 |
| A333 Grade9 | -100 | -75 |
| A333 Grade10 | -75 | -60 |
| A333 Grade11 | — | — |
Mechanical Properties:
| standard | mark | · Tensile Strength (Mpa) | yield strength(Mpa) | Elongation (%) | |
| lengthways | crosswise | ||||
| GB/T1898 -2003 | 16MnDG | 490-665 | ≥325 | ≥30 | — |
| 10MnDG | ≥400 | ≥240 | ≥35 | — | |
| 09DG | ≥385 | ≥210 | ≥35 | — | |
| 09Mn2VDG | ≥450 | ≥300 | ≥30 | — | |
| 06Ni3MoDG | ≥455 | ≥250 | ≥30 | — | |
| ASTM A333 | Grade1 | ≥380 | ≥205 | ≥35 | ≥25 |
| Grade3 | ≥450 | ≥240 | ≥30 | ≥20 | |
| Grade4 | ≥415 | ≥240 | ≥30 | ≥16.5 | |
| Grade6 | ≥415 | ≥240 | ≥30 | ≥16.5 | |
| Grade7 | ≥450 | ≥240 | ≥30 | ≥22 | |
| Grade8 | ≥690 | ≥515 | ≥22 | — | |
| Grade9 | ≥435 | ≥315 | ≥28 | — | |
| Grade10 | ≥550 | ≥450 | ≥22 | — | |
| Grade11 | ≥450 | ≥240 | ≥18 | — |
Chemical component:
| standard | mark | chemical component(%) | ||||||||||
| C | Si | Mn | P | S | Cr | Ni | Cu | Mo | V | Al | ||
| GB/T18984 -2003 | 16MnDG | 0.12-0.20 | 0.20-0.55 | 1.20-1.60 | ≤0.025 | ≤0.025 | — | — | — | — | — | — |
| 10MnDG | ≤0.13 | 0.17-0.37 | ≤1.35 | ≤0.025 | ≤0.025 | — | — | — | — | ≤0.07 | — | |
| 09DG | ≤0.12 | 0.17-0.37 | ≤0.95 | ≤0.025 | ≤0.025 | — | — | — | — | ≤0.07 | — | |
| 09Mn2VDG | ≤0.12 | 0.17-0.37 | ≤1.85 | ≤0.025 | ≤0.025 | — | — | — | — | ≤0.12 | — | |
| 06Ni3MoDG | ≤0.08 | 0.17-0.37 | ≤0.85 | ≤0.025 | ≤0.025 | — | 2.5-3.7 | — | 0.15-0.30 | ≤0.05 | — | |
| ASTM A333 | Grade1 | ≤0.30 | — | 0.40-1.06 | ≤0.025 | ≤0.025 | — | — | — | — | — | — |
| Grade3 | ≤0.19 | 0.18-0.37 | 0.31-0.64 | ≤0.025 | ≤0.025 | — | 3.18-3.82 | — | — | — | — | |
| Grade4 | ≤0.12 | 0.18-0.37 | 0.50-1.05 | ≤0.025 | ≤0.025 | 0.44-1.01 | 0.47-0.98 | 0.40-0.75 | — | — | 0.04-0.30 | |
| Grade6 | ≤0.30 | ≥0.10 | 0.29-1.06 | ≤0.025 | ≤0.025 | — | — | — | — | — | — | |
| Grade7 | ≤0.19 | 0.13-0.32 | ≤0.90 | ≤0.025 | ≤0.025 | — | 2.03-2.57 | — | — | — | — | |
| Grade8 | ≤0.13 | 0.13-0.32 | ≤0.90 | ≤0.025 | ≤0.025 | — | 8.40-9.60 | — | — | — | — | |
| Grade9 | ≤0.20 | — | 0.40-1.06 | ≤0.025 | ≤0.025 | — | 1.60-2.24 | 0.75-1.25 | — | — | — | |
| Grade10 | ≤0.20 | 0.10-0.35 | 1.15-1.50 | ≤0.030 | ≤0.015 | ≤0.15 | ≤0.25 | ≤0.015 | ≤0.50 | ≤0.12 | ≤0.06 | |
| Grade11 | ≤0.10 | ≤0.035 | ≤0.60 | ≤0.025 | ≤0.025 | ≤0.50 | 35.0-37.0 | — | ≤0.50 | — | — |
Welding of steel pipes at low temperature
We usually refer to steel applied at -10~-196°C as “low-temperature steel “, and “ultra-low temperature steel” used less than -196°C.” Low-temperature steel is required to have sufficient strength, plasticity and toughness in low-temperature working conditions, and good processing performance at the same time, mainly used for energy, petrochemical, offshore and other industries to manufacture welding structures operating at -20~-253°C low temperature, such as storing and transporting all kinds of liquefied gas containers.
For low temperature steel pipes (ASTM A333), commonly used welding methods are electrode arc welding, automatic submerged arc welding, tungsten argon arc welding, and gas fusion arc welding. The welding current should not be too large. At the same time, the temperature between the welding channels must be controlled. Welding should be performed with a small heat input and controlled below 20KJ / cm.
The energy of the welding line is also known as the welding heat input, which is the heat of the welding arc obtained per unit length of the weld.
Formula: E = U • I / v (joule / cm)
U: arc voltage (volts); I: welding current (amperes); V: welding speed (cm/min).
The energy of the welding line is an important factor affecting the mechanical properties of welded joints of low-temperature steel pipes. When the welding current and arc voltage increases, the energy of the welding line increases, as well as when the welding speed decreases. For low-temperature steel pipes, the energy of the welding line is too large, the toughness of the joint decreases rapidly, which makes the pressure vessel in low-temperature operation prone to instant damage. Therefore, welding current, arc voltage and welding speed must be strictly controlled.
Low-temperature steel pipe has a small tendency to hardening and a tendency to cold cracking due to its low carbon content and good weldability. However, too much energy from the welding line will cause the formation of a thick glass structure in the welding seam and heat-affected area and reduce the toughness at low temperature. Structural mutation and strong torques in manufacturing will cause high local stress and increase fragile equipment failure at low temperature. Therefore, the following tips should be taken into account in the welding process:
The energy of the small welding line can minimize overheating and prevent the appearance of thick fabric in the solder joint. Electrode arc welding generally adopts 12-15kj/cm, and submerged arc welding is usually 20KJ/cm. For this purpose, try to avoid 5 welding rods, submerged arc automatic welding plus choose 3.2 welding wire, welding rod arc welding each layer of about 2mm, automatic submerged arc welding about 2.5mm.
Straight step, multi-step quick press welding. It is to reduce overheating and the welding after front welding has the effect of tempering, so that grain refinement.
It is necessary to avoid the strong torque to avoid local stress concentration.
The welder should reduce the temperature between the layers between the weld bead as far as possible, avoid the weld bead in the high-temperature state for a long time, batch welding methods are appropriate.
Select the electrode and ultra-low hydrogen flow, before the solder dries according to the requirements, the welding electrode that has not been exhausted for more than 4 hours must be returned to the secondary storage for re-drying and use. In addition, the low-temperature steel welding rod for must be used according to the relevant standards for metal diffusion deposition of hydrogen reinspection, usually mercury method.
It should be properly preheated to at least 15 °C above. For winter construction or thick-walled steel pipe, for welding large-walled thick steel pipe, the preheating temperature is generally 50°C, and the temperature between channels is controlled between 50 150 and 150 °C.
The initiation of the arc shall be carried out by means of an initiation plate of the arc or in the groove, and shall not be carried out in non-welded parts. Heat treatment to relieve stress after welding steel pipes at low temperature can reduce the risk of brittle fracture of low-alloy steel welding products.
Commonly Used Low-Temperature Steel Pipe Welding Materials
16MnDR:
- J507GR, J507RH, ——E5015-G or E5016-G H10Mn2 SJ101 —— F5P4-H10Mn2 09MnNiDR:
- W707Ni, W807Ni —— E5515-N5 E7015-C1L, E7016-C1L F7P7-ENi2-Ni2
- H07MnNDR SJ603W —— F5P7-H07MnNiDR 08Ni3DR: For temperatures below -100°C, welding materials E7015-C2L and E7016-C2LF7P15-ENI3-NI3 are generally selected
SA-203 Gr. D is specified in ASME y-101 impact experiment experiment for E7016-C2L F7P15-ENi3-Ni3.
What is 09DG?
09DG is a type of low-carbon steel used mainly for manufacturing electrical appliances and machine parts in China.
The chemical composition of 09DG steel is as follows:
- Carbon (C): 0.07-0.12%
- Silicon (Si): 0.17-0.37%
- Manganese (Mn): 0.35-0.65%
- Phosphorus (P): <0.035%
- Sulfur (S): <0.035%
- Iron (Fe): balance
09DG steel has good weldability, bending performance, and surface quality. It is commonly used for automotive parts, electrical appliances, and other small machinery parts that require good formability, strength, and durability.
Overall, 09DG steel is a versatile and widely-used steel grade in China, particularly in the manufacturing of electrical and small machinery parts.