ASTM A178 ERW Tubes

Resistance welding is a process of welding by applying pressure through an electrode after the weldments have been assembled, using the resistance heat generated by the passage of electric current through the contact surfaces of the joints and the neighbouring areas.

• Standards: ASTM a178 (ASME Sa178)

Grade: Grade A Grade C Grade D

Size: OD 1/2in-5in(12.7-127mm)

Wall thickness:0.035in-0.360in(0.9-9.1mm)

• Chemical Composition of ASTM A178

Element %	ASTM A178 Gr A / SA178A	ASTM A178 Gr C / SA178C	ASTM A178 Gr D / SA178D
	Low carbon steel	Medium Carbon Steel	Manganess Steel
C	0.06-0.18	0.35 Max	0.27 Max
Mn	0.27-0.63	0.80 Max	1.00-1.50
P	0.035	0.035	0.030
S	0.035	0.035	0.015
Si	...	...	0.10 Min.

• Mechanical Property of ASTM A178

Item	ASTM A178 Gr A / SA178A	ASTM A178 Gr C / SA178C	ASTM A178 Gr D / SA178D
Tensile strength, min, ksi [MPa]	47[325]	60[415]	70[485]
Yield strength, min, ksi [MPa]	26[180]	37[255]	40[275]
Elongation in 2 in. or 50mm, min, %	35	30	30
For longitudinal strip tests a deduction for	1.50A	1.50A	1.50A
Each1⁄32-in[0.8mm] decrease in wall thickness below 5⁄16in. [8mm]
From the basic minimum elongation of the following percentage points shall be made

• Outside diameter and Wall Thickness Tolerance of ASTM A178 tubes

Outside Diameter tol		Wall thickness tol
OD < 50	±0.05mm	S < 4mm	±12.5%
OD > 50	±1%	4--20mm	+15/-12.5%
		S≧20mm	±12.5%

Types of resistance welding

1. Spot welding
Spot welding is assembled into a lap joint, and pressed between the two electrodes, the use of resistance heat to melt the base metal, the formation of welded joints resistance welding method. Spot welding should be used for thin plate welding.
Spot welding process:
(1) pre-pressure, to ensure good contact with the workpiece.
(2) power, so that the formation of welded nuclei and plastic ring.
(3) breakpoint forging, so that the molten core in the pressure under the continuous action of cooling crystallisation, the formation of dense tissue, no shrinkage, cracks in the welded joints.
2. Seam welding
Seam welding is assembled into a lap or butt joints, and placed between the two roller electrodes, the roller pressurised weldments and rotating, continuous or intermittent power supply, forming a continuous weld resistance welding method.
Seam welding should be used to weld a more regular seam, the requirements of the structure of the seal, plate thickness of the same in the following 3mm.
3. Butt welding
Butt welding is to make the weldment along the whole contact surface welding resistance welding method.
(1) resistance butt welding
Resistance butt welding is to assemble the weldment into a butt joint, so that the end face is in close contact with the use of resistance heat heated to a plastic state, and then the section and quickly apply the top forging force to complete the welding method.
Resistance butt welding should be used for simple cross-section, diameter or side length less than 20mm and strength requirements are not too high.
(2) flash butt welding
Flash butt welding is assembled into butt joints, connecting the power supply, so that its end face gradually close to achieve local contact, the use of resistance heat to heat these contact points, under the action of high current, resulting in flash, so that the end metal melting until the end of a certain depth within the scope of a predetermined temperature, power off and quickly apply the top of the forging force to complete the welding method.
Flash welding joint quality is better than resistance welding, the mechanical properties of the weld and the base material is comparable, and do not need to clean up the joint before welding the pre-welded surface.
Flash butt welding is commonly used in the welding of important weldments. Can be welded with the same metal, can also be welded dissimilar metals; can be welded 0.01mm wire, can also be welded 20000mm of metal rods and profiles.

A178 ERW Steel Pipe

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