What is a HFW steel pipe?

What is a HFW steel pipe?

High frequency welded pipe is based on solid resistance heat energy. Resistor thermal welding, using high-frequency current is generated in the workpiece so that the surface of the workpiece weld zone is heated to the melting or close to the plastic state, then applied (or not applied) upsetting force is achieved for such a steel pipe of the metal combination. HFW steel pipe production rate, welding speed of up to 30m/min. It is mainly used for the manufacture of pipes welded longitudinal seam or spiral seam. The welded pipe used high-frequency welding process of welding is mainly used for water, oil, natural gas, such as pressurized fluid delivery.

Sizes: 

  • Out Diameter:1/2″-24″
  • Wall Thickness: 1.65-20mm
  • Length: 3m-12m

Standard:

  • ASTM 5L
  • ASTM A53
  • ASTM A178
  • ASTM A500/501
  • ASTM A691
  • ASTM A252
  • ASTM A672
  • EN 10217

Advantage of HFW pipe

and In the welding process, HFW steel pipes do not need to add filling meta. So it has fast welding speed and high efficiency in production. HFW pipe is widely used in the fields of oil and gas transportation, oil well pipeline, building structure and various kinds of mechanical pipe. However, HFW steel pipe quality is affected by many factors, such as raw material and process. And the production quality control become difficult. So the yield and welding process still need to be improved continuously.

Diameter

Small diameter HFW steel pipe

Out diameter Sch 5 Sch 10 Sch 40
Inch mm Thickness Kg/mtr Thickness Kg/mtr Thickness Kg/mtr
1/2″ 21.3 1.65 0.81 2.11 1.01 2.77 1.29
3/4″ 26.7 1.65 1.03 2.11 1.30 2.87 1.71
1″ 33.4 1.65 1.31 2.77 2.12 3.38 2.54
1 1/4″ 42.2 1.65 1.93 2.77 3.15 3.68 4.11
1 1/2″ 48.3 1.65 1.93 2.77 3.15 3.68 4.11
2″ 60.3 1.65 2.42 2.77 3.98 4.81 5.31
3″ 88.9 2.11 4.58 3.05 6.54 5.49 11.45
3 1/2″ 101.6 2.11 5.25 3.05 7.52 5.74 13.77
4″ 114.3 2.11 5.25 3.05 7.52 5.74 13.77
5″ 141.3 2.77 9.50 3.40 11.74 6.55 22.10
6″ 168.3 2.77 11.47 3.40 14.04 7.11 28.68
8″ 219.1 2.77 14.99 3.76 20.25 8.18 43.16

Large diameter HFW steel pipe

OD WT
Inch mm 8 5/8″ 219.1mm 10 3/4″ 273.1mm 12 3/4″ 325.0mm 14″ 355.6mm
0.157 4.0
0.197 5.0
0.236 6.0
0.276 7.0
0.315 8.0
0.354 9.0
0.394 10.0
0.133 11.0
0.492 12.5
0.551 14.0
0.630 16.0
0.689 17.5
0.748 19.0
0.787 20.0

High frequency welding

HIGH-FREQUENCY WELDING is a welding process in which the heat source used to melt the joining surfaces is obtained from high-frequency (HF) alternating current (ac) resistance heating.

Steel weld gap control
Adjusting the amount of pressing the squeeze roll is maintained across the weld flush with the opening angle of 7 degrees or less, the gap control between 1-3 mm. Weld control is too large, it may appear poor welding, weld cracking produce incomplete fusion or weld control is too small, due to the excessive heat, weld likely to cause burning, molten metal splash, build-up is too large, affecting the quality of welding. (Splatter reasons: melt extrusion tube side, the internal pressure is greater than the surface of the weld steam pressure) 
Regulation of high-frequency induction loop position
Induction coil placement should be in the same center line pipe, induction loop front roll center line distance from the squeeze, squeeze rollers under the premise does not burn , depending on pipe size as close, too far away when the heat affected zone width, weld strength will decrease. Coupled induction coil more tightly as possible, the selection of a single circle, should be equal to the width of the induction coil pipe diameter. Optional lap or two laps great impact on high frequency oscillation frequency and output efficiency. 
Impedance (also known as magnet) position control
Impedance is a group or a special magnet whose cross-sectional area of 70% attributable to the inner diameter of the steel pipe section. Its role is to strengthen the electromagnetic induction, eddy currents concentrate the heat weld edges. Sometimes add some magnets outside the weld, can also play a supporting role. Magnet permeability on temperature is large, the lower the temperature the higher the permeability. Magnet should be placed in the heating section V-zone, squeezing front roll center position, the position of the magnet and the magnetic permeability of welded directly affect the efficiency and weld quality. 
Heat output control
High-frequency power input to the heat pipe weld area called the input of heat, lack of heat input welding speed is too fast, can not reach the edge of the pipe welding temperature, the formation of incomplete fusion or penetration of the crack but excessive heat input when welding speed is too slow, too prone to burning, so that the weld breakdown, causing metal splash, the formation of pores. By adjusting the speed of the high-frequency voltage or welding method, the size of the control input of heat, the steel pipe weld neither appear nor appear incomplete penetration welding wear phenomenon, reaching the welding quality requirements.

The high-frequency welding for carbon steel welded pipe production has been 40 years of history. Having a large power supply power, high-frequency welding of different material, diameter and wall thickness of a steel pipe can reach a higher welding speed (highest ratio TIG welding speed is more than l0 times higher). Therefore, the production of general-purpose high-frequency welding pipe has higher productivity because of the high-speed high-frequency welding difficult, given to the the burr removal of welded pipe within, which is the current high-frequency welded steel pipe is not yet for the chemical industry, nuclear industry accepted one of the reasons. From the welding material, high-frequency welding can weld all types of steel pipes.

High frequency welded pipe typical process

HFW steel pipe production process depends mainly on product variety, the need to go through a series of processes from raw material to finished product, complete these processes require various machinery and equipment and welding, electrical control, detection devices, equipment and apparatus in accordance with different process The process requires a variety of reasonable layout, high frequency welded pipe typical process: uncoiler – strip leveler – head and tail the shear – strip butt – Looper hopper – molding – welding – Clear glitch – Sizing – Testing – fly cut – the first test – pipe straightening – pipe sections processing – hydrostatic testing – flaw detection – printing and coating – finished.

Weld Joint quality factor of HFW pipe

As there is no need to add filler metal during the welding process of HFW steel pipe, it has the advantage of high welding speed and high production efficiency, and it is widely used in oil and gas transport, oil pipelines, structures and various mechanical pipe and other fields. But HFW steel pipe can be affected by the quality of raw materials and processes, and many other factors, it is difficult to control the production quality, the yield and the welding process still needs to continuously improve.

The impact of raw materials for welding quality is listed as below:

1. Materials smelting method

Using the traditional method of production, for converter steel, N-containing is high, impurity elements is more, cold brittleness is big and sensitivity increases, which makes the welding quality degraded; for boiling steel, deoxidation incompletely, O-containing is high, S and P and other impurities are unevenly distributed, local content will be exceeded, aging sensitivity and cold crisp sensitivity become larger, hot cracking tendency also increases. So now the general pipe materials are smelted by the blowing alkaline converter or electric furnace and processed by vacuum degassing and Ca treated killed steel, and require non-metallic inclusions in steel should generally be less than 2.0, no ribbon fiber structure and no significant segregation.

2. Chemical composition of raw materials

Reducing C, S and P content and increasing the ratio of Mn/Si can improve the weldability the strip materials effectively. High C content is too easy to form segregation and banded structure, and reducing the C content can improve the toughness and resistance to HIC (HIC) performance. S is extremely harmful elements in steel, which can significantly undermine the weldability of steel, causing high temperature cracking, and weld porosity and loose phenomenon. With high content of the sulfide, the S inclusions increase and it easily leads to HIC and SSC (Sulfide Stress cracking). And improve the ratio of Mn\si can reduce weld cracking tendency and improve the quality of welded steel pipe.

3. Carbon equivalent (Ceq) of steel

The carbon equivalent of steel refers to convert the the content of alloying elements which will affect the hardness, cold cracking and brittleness into the equivalent content of carbon. By the estimation of carbon equivalent steel and cold cracking sensitivity index, it can palay an important guiding role in judging the welding performance of steel.

HFW steel pipe defects in production

HFW welded steel pipes are widely preferred in Oil, Natural Gas, Water and other liquids transportation and distribution lines, heating, cooling, ventilation piping and steel structures for construction and other general purposes by means of precise production tolerances and high capacity manufacturing method.

High Frequency Welded pipe - What is a HFW steel pipe?

  • High frequency welding influence on welding quality of steel pipe
  • ERW Pipe Manufacturing Processes
  • Welded Tube and Pipe Manufacturing Processes
  • Electric resistance welding at a glance

Finishing Operations: Plain-End, Square Cut or bevelled.

Surface Condition

  • Black self-colored / uncoated
  • Mill protective coating (varnish) on outside surface
  • Three Layer Extruded Polyethylene – Polypropylene coating (plus rough coating)
  • Fusion Bond Epoxy Single – Dual Layer coating
  • Liquid Epoxy coating

HFW steel pipe defects in production

Technical requirements For oil and gas transport For low pressure fluid conveying 
Material Gr.b Gr.b
Pipe body diameter D<508mm, ±0.75%; D≥508mm, ±0.75% D≤168.3, ±1.0%;  168.3<D≤508,±0.75%;  
Wall thickness D<508mm,+15.0%,-12.5%; D≥508mm, +17.5%,-10% ±12.5%
Bending ≤0.2% ≤0.2%
Ovality D≥508mm,≤±1% ≤±0.75%
Bevel ≤1.59mm ≤5mm
Hydrostatic testing  100%  100% 
Nondestructive testing 100% non-destructive weld inspection Ultrasonic flaw detection is 100%
  • Yield strength of the N80 is higher than the J55 up to 173 ~ 206 MPa.
  • On the same area of the sample, the elongation of N80 is higher than J55.
  • Under the same size, the same sample orientation, the same minimum sample size, J55 grade couplings, coupling stock, coupling material, semi-finished and coupling attachment material can absorb lower than N80 steel grade.
  • The nondestructive testing methods of seamless pipe,coupling stock, welded tube with J55 and N80 is differeent.
  • J55 and N80 steel grade is not the same color: length greater than or equal 1.8m, J55 painted a bright green, N80 painted a red;
  • J55 chosen by the manufacturer, or organize according to the order specified length normalized (N), normalizing and tempering (N & T) or quenching and tempering (Q & T). N80 is a whole, full-length heat treatment is mandatory. By the manufacturer selected for normalizing (N) or normalizing and tempering (N & T) + quenching (Q).

Application Areas

HFW welded steel pipes are widely preferred in Oil, Natural Gas, Water and other liquids transportation and distribution lines, heating, cooling, ventilation piping and steel structures for construction and other general purposes by means of precise production tolerances and high capacity manufacturing method.

Pipe Length

Yaang is able to manufacture and supply high frequency welded pipes up to 16 m. in unit length.

Pipe Coating

Coating mills apply pipe coatings to protect the line pipe from corrosion. Often, the coating mill is located adjacent to the pipe mill, so line pipe moves directly from the pipe manufacturer to the coating facility.

Resource:

  • testing facilities for fracture mechanics studies
  • corrosion & metallurgical test equipment
  • non-destructive testing
  • process advice & troubleshooting
  • tailored training courses

Differences between ERW and HFW steel pipe

First is to know the differences of the ERW, HFW welding processes.
ERW welding process refers the heat generated by the resistance to current flow that pass through the jointed metals. So a large current is needed to electrify the whole surface of the steel plate or coil to the length of welding. In the ERW welding process, the electric current that pass through the entire conductor is at 50/60 Hz.
HFW welding process is not the same case with the high-frequency process, since it’s only a section of the steel metals is heated by the induction of electric coil. High-frequency is generated by either AC or DC current. In these cases, the constant current welding generator and constant voltage high-frequency welding generator are used.
Constant current welding machine generates power in 100-800 kHz. In the elder processes, the conversion of 60 Hz, AC current to HF was done by using triode and tank circuits. New welding machine uses metal oxide silicon, filed-effect transistors, usually associated with parallel resonant circuit. The constant voltage version generators use insulated gate bipolar transistors designed to power about 2000 kW with frequency rages of 100-600 KHz.

There are two distinct features of HF current than 60 Hz line current:

While the 60 Hz line frequency current flow through the whole conductor but HF current flow only on the surface of the conductor, so it is “skin effect”.
While two conductors carrying HF current are placed close to one another an the current concentrates on the two adjacent surfaces of the conductors, it is “proximity efect”.
HFW current distribution: The current flows in the surface of the metal or the conductor. Both conductors are placed in close proximity with most of the HF current flowing on the adjacent sides of the conductors.

HFW is required in API 5L PSL2 ERW steel pipe

According the API 5L and ISO 3183 specification, for PSL 2 pipes in welded process the HFW welding is a mandatory requirements for ERW steel pipes. As it is an improvement from the inherent problems of hardness, lack of fusion and susceptibility of stress corrosion cracking (SCC).

ERW steel pipe includes HFW steel pipe

ERW is general designation of resistance welded steel pipes. It can be sorted into two types: alternated current welding (AC) and direct current welding (DC). According to different frequency, AC welding can be divided into low frequency welding, intermediate frequency welding, ultra frequency welding and high frequency welding. The high frequency welding (HFW) is mainly used in ordinary or thin wall steel pipe. It includes contact welding and induction welding. Direct current welding is generally used for small caliber steel tubes. In general, HFW is one of ERW production methods, it adopts the high frequency welding process. So, ERW steel pipe includes HFW steel pipe.

The difference between double submerged arc welding(dsaw) and high frequency difference(HFW)

The difference between double submerged arc welding (dsaw) and high frequency difference (HFW) is mainly manifested in the appearance of the weld appearance, Double submerged arc welding steel pipe in appearance is with a slight indentation strip, mainly in steel interior. Straight seam submerged arc weld pipe is higher than the base material for the neat 1-3mm weld. In appearance frequency steel tube smooth, non-oxide adhesion. In the weld, high-frequency straight seam steel pipe weld high measure to squeeze flow resistance, the jagged serrate irregular weld, this weld is “scratch” before they go out, leaving a flat weld removal of trace.

High Frequency Welded pipe banner - What is a HFW steel pipe?
High Frequency Induction (HFI) Welded Pipe

In addition, two-sided submerged arc welding and high frequency difference is also reflected in the production process, the use of different raw materials, different molding process, the welding process is different from different production units, production of different scope. Sided submerged arc welding straight seam steel production process only with JCOE molding process molding process complex, forming efficiency relative to the low-frequency welded pipe, so the manufacturing cost is higher than the high-frequency straight seam welded steel pipeHigh-frequency straight seam welded steel pipe (ERW) production process is simple, a single specification. Double-sided submerged arc straight seam steel pipe forming process is JCOE cold forming, features that make the steel at 50mm gradually forming, J, C, O, E represents the image of straight seam steel submerged arc forming process. Frequency straight seam steel pipe forming process for the multi-pass rolls, squeeze both ends of the strip, and finally justified the strip cold molding process, the molding process is characterized by uninterrupted, continuous welding. Submerged arc welding process is characterized by using steel wire electric effect and melt together, as filler welding. Frequency straight seam steel pipe welding process is characterized by the use of high frequency current skin effect rapid warming strip ends in a short time under the action of external forces strip from melting together.

Double Submerged arc welded pipe banner - What is a HFW steel pipe?
Double Submerged Arc Welded (DSAW) steel pipe

Frequency straight pipe production unit for the same lines of uninterrupted production line efficiency, and submerged arc welding straight seam steel pipe has up to 15 intermittent production processes complete unit. Frequency straight seam steel pipe production specifications fewer production thinner.

Effect of Different Heat Treatment Processes on Groove Corrosion of HFW Welded Pipe

The potential difference between the weld seam of HFW welded pipe and the heat affected zone and the base metal is the main cause of groove corrosion; through effective heat treatment, the microstructure of the weld, heat affected zone and the base metal can be uniform and grain refinement can be significantly reduced. Groove corrosion sensitivity coefficient; different heat treatment conditions, anti-groove corrosion sensitive properties for the quenched and tempered heat treatment> (medium frequency induction, resistance furnace) heating + water cooling> welding state.
HFW welded pipe has been widely used in downhole casing and oil and gas gathering pipelines because of its advantages such as economical efficiency and high dimensional accuracy. However, due to the difference in electrochemical performance between the weld zone and the base metal zone, the HFW welded pipe is prone to weld-groove-like selective corrosion under the service environment. Therefore, it is of great significance to study the electrochemical behavior of the groove corrosion of the welded pipe, the relationship between the heat treatment process and the microstructure, and to obtain a method for reducing the corrosion sensitivity of the groove of the welded pipe. The author chooses HFW welded pipe as the research object to study the effect of different heat treatment processes on the corrosion of the welded pipe groove, and provides a reasonable basis for effectively controlling the corrosion resistance of the HFW welded pipe against trenches.
The average values of channel corrosion sensitivity coefficient α of HFW pipes under different heat treatment processes were 1.32, 1.21, 1.18, 1.14 and 1.12, respectively. The non-heat-treated specimen has the highest sensitivity to trench corrosion; the material is austenitized by heating at intermediate frequency and resistance furnace, and after the water-controlled cold and heat treatment, the trench sensitivity of the weld is reduced. 

Source: China HFW Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.ugsteelmill.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@ugsteelmill.com

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References:

  • https://www.yaang.com

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