GB/T 18984 Seamless Steel Tubes for Low-temperature-service Piping

Standard: GB/T 18984
Equivalent Standard: ASTM A333/A333M, JIS G3460, JIS G3464, ISO 9329-3
Material: 16MnDG

Chemistry Composition

C, %	Mn, %	P, %	S, %
0.30 max	0.40-1.06	0.025 max	0.025 max

Mechanical Properties

Tensile Strength , MPa	Yield Strength, MPa	Elongation, %	Hardness, HB
380 min	205 min	35 min	163 max

Outside Diameter & Tolerance

Hot rolled	Outside Diameter, mm	Tolerance, mm
	OD≤101.6	+0.4/-0.8
	101.6＜OD≤190.5	+0.4/-1.2
	190.5＜OD≤228.6	+0.4/-1.6
Cold Drawn	Outside Diameter , mm	Tolerance, mm
	OD＜25.4	±0.10
	25.4≤OD≤38.1	±0.15
	38.1＜OD＜50.8	±0.20
	50.8≤OD＜63.5	±0.25
	63.5≤OD＜76.2	±0.30
	76.2≤OD≤101.6	±0.38
	101.6＜OD≤190.5	+0.38/-0.64
	190.5＜OD≤228.6	+0.38/-1.14

Wall thickness & Tolerance

Hot rolled	Outside Diameter , mm	Tolerance, %
	OD≤101.6, WT≤2.4	+40/-0
	OD≤101.6, 2.4＜WT≤3.8	+35/-0
	OD≤101.6, 3.8＜WT≤4.6	+33/-0
	OD≤101.6, WT>4.6	+28/-0
	OD>101.6, 2.4＜WT≤3.8	+35/-0
	OD>101.6, 3.8＜WT≤4.6	+33/-0
	OD>101.6, WT>4.6	+28/-0
Cold Drawn	Outside Diameter , mm	Tolerance, %
	OD≤38.1	+20/-0
	OD>38.1	+22/-0

GB/T 18984 specifies the classification, code, order content, size, shape, weight, technical requirements, test methods, inspection rules, packaging, marking and quality certificate of seamless steel pipes for low temperature pipelines. GB/T 18984 is applicable to seamless steel pipes for low-temperature pressure vessel pipes and low-temperature heat exchanger pipes with working temperature -45°C level to -196°C level.

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.