Electric Resistance/ Fusion Welded (ERW and EFW)

Electric resistance welding (ERW) refers to a group of welding processes such as spot and seam welding that produce coalescence of faying surfaces where heat to form the weld is generated by the electrical resistance of material combined with the time and the force used to hold the materials together during welding

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ERW

ERW steel pipe is manufactured through low or high frequency resistances Electric Resistance. Welding seam is in longitudinal. During the ERW pipe welding processes, the electric current will make the heat when flow through the contact surface of the welding area. It will heat the 2 edges of the steel to a point that the edges can form a bond. Meanwhile with the combined pressure, the edge of the pipe billet steel melted and extruded together.

ERW steel pipe used for transporting gas and liquid objects such as oil and gas, could meet the low and high pressure requirement. In recent years, with the development of ERW technology, more and more ERW steel pipe used in the oil and gas fields, automobile industry and so on.

ERW pipe manufacturing process includes HFW. ERW have low, medium, high frequency welding processes, and HFW is especially for high-frequency electric resistance welding. The differences between ERW and HFW steel pipe, is EFW is a type of ERW process for ordinary and thin-wall thickness steel pipes.

HFW

High frequency welding (HFW) steel pipe is that ERW pipe produced with a welding current frequency equal to or greater than 70 kHZ. Through high-frequency current welding resistance, the heat generated in the contact objects, so the objected surface are heated to the plastic state, then with or without forging to achieve a combination of steels. HFW is a solid resistance heat energy. The high frequency current pass through the metal conductor, will produce two peculiar effects, skin effect and proximity effect. And HFW process is to use the skin effect to concentrated on steel object surface, use proximity effects to control the position and the power of the high-frequency electric current flow path. Since the speed is very high, the contacted plate edge could be heated and melted in shore time, then extruded through docking process.

EFW

Electric Fusion Welding (EFW) steel pipe refers to an electron beam welding, the use of high-speed movement of the electron beam directed impact kinetic energy is converted to heat the workpiece so that the workpiece leaving the melt, the formation of the weld. It is mainly used for welding dissimilar steel welding sheet or which high power density, metal weldment can rapidly heated to high temperatures, which can melt any refractory metals and alloys. Deep penetration welding fast, heat-affected zone is extremely small, so small performance impact on the joints, the joint almost no distortion. But it has a requirement on a special welding room because welding using X-rays.

Highlights of the ERW/ EFW Pipe

Specification

• ASME 36.10, ASME 36.19 are the key specifications covering the standardization of dimensions of welded and seamless wrought steel pipe. ASME B16.25 covers the preparation of butt weld connections between pipes and ASME B16.49 covers the marking details.

Advantage

• Customize size that meet exact design requirement (Diameter, Thickness, Length).

• Greater strength, double welded seam has the effect of a spiral band around the pipe.

• Greater pressure resistant, Stress, and Friction. The spiral band has the effect of adding greater structural strength, 25% higher pressures than longitudinally welded pipes and ERW Pipes.

Disadvantage

• Spiral pipe is harder to weld

• Spiral pipe have a longer weld and are therefore prone to more failures

• Spiral pipe are more exposed to propagating cracks

• Spiral pipe have problems in pigging operations

Length of Pipes

• Piping lengths from the factory not exactly cut to length but are normally delivered as:

○ Single random length has a length of around 5-7 meter

○ Double random length has a length of around 11-13 meter

Shorter and longer lengths are available, but for a calculation, it is wise, to use this standard lengths; other sizes are probably more expensive.

Ends of Pipes

• For the ends of pipes are 3 standard versions available.

○ Plain Ends (PE)

○ Threaded Ends (TE)

○ Beveled Ends (BE)

The PE pipes will generally be used for the smaller diameters pipe systems and in combination with Slip On flanges and Socket Weld fittings and flanges.

The TE implementation speaks for itself, this performance will generally used for small diameters pipe systems, and the connections will be made with threaded flanges and threaded fittings.

The BE implementation is applied to all diameters of buttweld flanges or buttweld fittings, and will be directly welded (with a small gap 3-4 mm) to each other or to the pipe. Ends are mostly be beveled to angle 30° (+ 5°/ -0°) with a root face of 1.6 mm (± 0.8 mm).

Other Properties

• An effective pre and post weld heat treatment is vital. The use of pre heat together with a carefully selected surface preparation and the use of low hydrogen, hydrogen tolerant consumable wire eliminate the risk of hydrogen cracking during welding. Post weld heat treatment is used to control the more significant problem of the transformation of the substrate to un-tempered martensitic structure during the process.

Materials

• ASTM A53 (Gr. A, B)

• API 5L Welded -Grades (B, X42, X46, X52, X56, X60, X65 and X70) PSL 1, PSL 2 (PSL2 shall be in HFW process)

• ASTM A252

• ASTM A134

• ASTM A135

• EN 10219 (S275, S355)

• A671 (CC60, CC65)

• A672 (CC60, CC65)

• ASTM A691

• API 5L Grades X80

• ASTM A312 (TP304/304L, TP316/316L, TP321, TP321H, TP347, TP347H)

• ASTM A790

• ASTM A358 (TP304/304L, TP316/316L, TP321, TP321H, TP347, TP347H)

• ASTM A928 (UNS S31803, UNS S32750, UNS S32760)

Standard

ASME 36.10, ASME 36.19 are the key specifications covering the standardization of dimensions of welded and seamless wrought steel pipe. ASME B16.25 covers the preparation of butt weld connections between pipes and ASME B16.49 covers the marking details.

ASME 36.10

This standard covers the standardization of dimensions of welded and seamless wrought steel pipe for high or low temperatures and pressures. Pipe NPS 12 (DN 300) and smaller have outside diameters numerically larger than corresponding sizes. In contrast, the outside diameters of tubes are numerically identical to the size number for all sizes.

The size of all pipe is identified by the nominal pipe size. The manufacture of pipe NPS ⅛ (DN 6) to NPS 12 (DN 300), inclusive, is based on a standardized outside diameter (O.D.). This O.D. was originally selected so that pipe with a standard O.D. and having a wall thickness that was typical of the period would have an inside diameter (I.D.) approximately equal to the nominal size. Although there is no such relation between the existing standard thickness - O.D. and nominal size - these nominal sizes and standard O.D.s continue in use as "standard." The manufacture of pipe NPS 14 (DN 350) and larger proceeds on the basis of an O.D. corresponding to the nominal size.

ASME 36.19

This Standard covers the standardization of dimensions of welded and seamless wrought stainless steel pipe for high or low temperatures and pressures.

Pipes NPS 12 (DN 300) and smaller have outside diameters numerically larger than their corresponding sizes. In contrast, the outside diameters of tubes are numerically identical to the size number for all sizes. The wall thicknesses for NPS 14 through 22, inclusive (DN 350-550, inclusive), of Schedule 10S; NPS 12 (DN 300) of Schedule 40S; and NPS 10 and 12 (DN 250 and 300) of Schedule 80S are not the same as those of ASME B36.10M. The suffix S in the schedule number is used to differentiate B36.19M pipe from B36.10M pipe. ASME B36.10M includes other pipe thicknesses that are also commercially available with stainless steel material.

API 5L

ANSI / API 5L specifies the manufacture of two product levels (PSL1 and PSL2) of seamless and welded steel pipe for the use of a pipeline in the transportation of petroleum and natural gas. For material use in a sour service application, refer to Annex H; for offshore service application, refer to Annex J of API 5L 45th Edition.

Grades covered by this specification are A25, A, B and "X" Grades X42, X46, X52, X56, X60, X65, X70, and X80. The two digit number following the "X" indicates the Minimum Yield Strength (in 000's psi) of pipe produced to this grade.