ERW steel pipes means Electric Resistance Welded Pipes. ERW steel pipes and tubes are used. ERW steel pipes and tubes are used in various engineering purposes, fencing, scaffolding, line pipes etc. ERW steel pipes and tube are available in various qualities, wall thicknesses, and diameters of the finished pipes.
Manufacturing Process of ERW Pipe
Electric resistance welded (ERW) pipe is manufactured by cold-forming a sheet of steel into a cylindrical shape. Current is then passed between the two edges of the steel to heat the steel to a point at which the edges are forced together to form a bond without the use of welding filler material.

TYPICAL ERW PIPE MANUFACTURING PROCESS

Our manufacturing process generally involves the following stages in a step by step procedure.

SLITTING

HR Coils are slitted to pre-determined widths for each and every size of pipes

Round forming

UNCOILING, END SHEARING AND WELDING

The slitted coil is uncoiled at the entry of ERW mill and the ends are sheared and welded one after another. This results in a single endless strip.

FORMING

The slitted coils are initially formed into U shape and after that into a cylindrical shape with open edges utilizing a series of forming rolls.

Welding

WELDING

In this stage, the open edges are heated to the forging temperature through high-frequency, low-voltage, high current and press welded by forge rolls making perfect and strong but weld without filler materials.

 

Seam Annealing

DE BEADING

In this stage, the weld flash on top and inside (if required) is trimmed out using the carbide tools.

SEAM ANNEALING

If required, the welding portion and heat affected zone is put to normalizing and then are cooled down in a air cooling bed.

SIZING

After water quenching, slight reduction is applied to pipes with sizing rolls.

This results in producing desired accurate outside diameter.

 

Pipe beveling

Pipe cutting

CUTTING

In cutting stage, the pipes are cut to required lengths by flying cut off disc/saw cutter.

END FACING AND BEVELLING

This is usually stage, where the pipes ends are faced and bevelled by the end facer.

All these processes are continuous with automatic arrangements. These plain ended tubes further go for processing as per the customer requirements such as galvanizing, threading, black varnishing and more.

ERW steel pipes and tube are available in various qualities, wall thicknesses, and diameters of the finished pipes.

ERW pipe technical requirements

ERW steel pipes and tubes are used in various engineering purposes, fencing, scaffolding, line pipes etc.

• 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).

ERW pipe welding process

Pipes in industrial production and civilian sectors have a wide range of applications, for water, oil, gas and other fluid transported using the pipeline has a convenient, fast and low cost several advantages, especially in long-distance transport process, which can show it advantages in the long course of the inner wall of the pipe is formed on the deposition or dirt.

If the pipeline will form scale or private dirt, will form the inner wall of the pipeline grease or wax accumulated in the industrial gas pipeline will also form coke coke and other dirt. The dirt deposited in the pipeline fluid greatly increases the resistance during transport not only the transmission efficiency and the power consumption required for transporting fluids also increased significantly. Dirt will cause corrosion on the pipe material and cause serious damage to pipe rupture, transmission fluid leakage losses, and even cause shutdown. Pipeline corrosion is often caused by contaminated pipeline transportation Economically, the main safety significant harm. With the increase in pipe and pressure pipe increased age increased, run run, drip, scaling, corrosion, plugging and explosion emerging pipeline not only will these failures appear normal production and life will be adversely affected to people’s lives and property caused irreparable damage, so the need for regular cleaning of the pipeline. Clean pipes according to the specific circumstances of different scaling using a variety of methods, such as using acid, alkali or surfactant aqueous solution of chemicals closed loop pipeline cleaning, you can also use ultrasound, water jet, or other physical means to dirt peeled and removed from the wall but lighter in the early stages of pipe scale adoption Erw pipe welding process may be a simple, low cost but good effect method. Erw pipe welding process in the industry, also known as Erw pipe welding process.

Pigging is a special polyurethane material shaped like a bullet of materials, shrink resistance, high strength. Erw pipe welding process technology to remove pipe scale, sediment or foreign body for the purpose of a technology. Its working principle is put into Pig launchers after launching the forward direction of the media in Pig pressure difference, the formation of forward thrust, the Pig advancing along the pipeline, during operation, Pig slightly deformed. Pig itself or its attachments in the customs fouling constantly in contact with the wall, squeezing against fouling, scrapers, erosion, vibration broken, remove the pipe structure, sediment and foreign matter. At the same time, the medium in the tube wall through said cooking Pig gap formed annulus is formed when the high speed jet, its role in the front region is formed like a vacuum, is conducive to the operation of Pig, and the scraped The impact of fouling slag, stirred and timely discharge tube, effectively prevents dirt accumulation of residue in the tube to avoid the clogging phenomenon.

Pigging is characterized because it is composed of polyurethane foam with good flexibility so that, in the conduit line of the elbow, tee fittings and small pipe section can be bent easily through and has good wear resistance, it is possible to walk long distances in the pipeline. In cleaning up to several kilometers and the shape of complex mechanical cleaning pipes or jet cleaning has difficulty using Erw pipe welding process can often better to complete cleaning tasks.

Electric resistance welding at a glance

PROCESS, POWER SUPPLY, AND WELD ROLL BASICS

Several electric resistance welding (ERW) processes are available for tube and pipe production. While each process has different characteristics, all ERW processes have one thing in common–all of them produce a forged weld.
A forged weld is created by applying a combination of heat and pressure, or forging force, to the weld zone. A successful forged weld uses the optimum amount of heat, which is normally slightly less than the melting point of the material, and a nearly simultaneous application of circumferential pressure to the section, which forces the heated edges together (see Figure 1).
As the name implies, the heat generated by the weld power is a result of the material’s resistance to the flow of electrical current. The pressure comes from rolls that squeeze the tube into its finished shape.
The two main types of ERW are high-frequency (HF) and rotary contact wheel.

THE BASICS OF HF WELDING

The two main aspects of HF welding are processes and power supplies. Each of these can be broken down further into subcategories. Processes. The two HF welding processes are HF contact and HF induction. In both processes, the equipment that provides the electrical current is independent from the equipment that supplies the forge pressure. Also, both HF methods can employ impeders, which are soft magnetic components located inside the tube that help to focus the weld current in the strip edges.

HF Induction Welding. In the case of HF induction welding, the weld current is transmitted to the material through a work coil in front of the weld point (see Figure 2). The work coil does not contact the tube–the electrical current is induced into the material through magnetic fields that surround the tube. HF induction welding eliminates contact marks and reduces the setup required when changing tube size. It also requires less maintenance than contact welding.
It is estimated that 90 percent of tube mills in North America use HF induction welding.
HF Contact Welding. HF contact welding transfers weld current to the material through contacts that ride on the strip (see Figure 3). The weld power is applied directly to the tube, which makes this process more electrically efficient than HF induction welding. Because it is more efficient, it is well-suited to heavy-wall and large-diameter tube production.
Power Supplies. HF welding machines also are classified by how they generate power. The two types are vacuum tube and solid-state. The vacuum tube type is the traditional power supply. Since their introduction in the early ’90s, however, solid-state units have quickly gained prominence in the industry. It is estimated that between 500 and 600 of each type are operating in North America.

THE BASICS OF ROTARY CONTACT WHEEL WELDING

In rotary contact wheel welding, the electrical current is transmitted through a contact wheel at the weld point. The contact wheel also applies some of the forge pressure necessary for the welding process.
The three main types of rotary contact wheel welders are AC, DC, and square wave. In all three power supplies, electrical current is transferred by brush assemblies that engage slip rings attached to a rotating shaft that supports the contact wheels. These contact wheels transfer the current to the strip edges.
AC Rotary Contact Wheel Welding. In an AC rotary contact wheel welding machine, the current is transferred through the brushes to the rotating shaft, which has a transformer mounted on it. The transformer reduces the voltage and increases the current, making it suitable for welding. The two legs of the transformer’s output circuit are connected to the two halves of the rotating contact wheel, which are insulated from each other. The strip completes the circuit by acting as a conductor between the two halves of the wheel.
Traditional rotary contact wheel welders used 60-hertz AC, or common line current. A drawback to this system is that the current–and therefore the weld heat–rises and falls, limiting the speed at which the tube can be welded. An AC sine wave reaches its maximum amplitude briefly, producing weld heat that varies just as the sine wave does (see Figure 4).

To help even out the heat variation, motor generator sets were introduced to create AC at higher frequencies. Some of the frequencies used were 180, 360, 480, and 960 Hz. A few solid-state units also were produced to generate higher-frequency currents. An AC sine wave at 960 Hz reaches its maximum amplitude 1,920 times per second, as opposed to 120 times per second with a 60-Hz signal. The 960-Hz sine wave produces heat with a much more consistent temperature.

DC Rotary Contact Wheel Welding. The next step in rotary contact wheel welding was the DC power supply. The power produced has a nearly constant amplitude. Although this solves the problem of varying heat, a major drawback is that higher maintenance costs are associated with this type of welding machine.

Because it is not possible to change the voltage of DC with a transformer, it is necessary to transmit the high-amperage, low-voltage weld current into the shaft through a large number of brushes (92 for DC versus 8 for AC) with a high current density. Transmitting high-amperage, low-voltage current produces excess (waste) heat that causes heavy wear, resulting in the high maintenance costs mentioned previously.

Square Wave Rotary Contact Wheel Welding. The latest step in the evolution of rotary contact wheel welding is the square wave power supply. This method combines the consistent weld heat of DC with the lower maintenance associated with AC units (see Figure 5). While rotary contact weld methods preceded the more commonly used HF welding processes, they still have a vital role in specialty welding applications. Rotary contact welding is useful for applications that cannot accommodate an impeder on the ID of the tube. Examples of this are small-diameter refrigeration-grade tube and tube that is painted on the ID immediately after the welding process.

HOW MANY ROLL UNITS ARE NEEDED?

The types of weld pressure rolls, or squeeze boxes as they sometimes are called, that apply the pressure required for the weld are as varied as the welding units used to supply the heat. Squeeze boxes for rotary contact wheel welding typically have two or three roll units, with the contact wheel serving as one of the rolls.
The number of rolls in the weld squeeze box is proportionate to the size and shape of the product being welded. There are no hard and fast rules; however, common guidelines for round tube or pipe size ranges are as follows:

• 3/8 to 2 in. uses two-roll units.
• 1/2 to 3 1/2 in. uses three-roll units.
• 2 to 10 in. uses four-roll units.
• Larger than 10 in. uses five or more rolls.

Today, much more so than in the past, many shapes–square, rectangular, hexagonal–are welded in the finished shape rather than being reshaped after being welded round. The weld boxes used for the shapes are custom-designed for each application and usually have no more than five rolls.

ERW PIPE ISSUES AND DEFECTS

ERW pipe issues and defects is related to raw materials, production methods, process conditions, equipment status and personnel. Product defects that appear in the production process by the above factors and constraints. This product defects can be divided into roughly two categories: one for product defects, that defects production of the product itself exist inconsistent sets of product standards; a class of defects generated during the production process defects, it do not form the product requirements of the standard items, but also an issue of product quality, and its trend of development will inevitably lead to product defects. Therefore, this defect is not allowed in the production process.
Process defects 
No burr: burr welds. Outer burr is generally better when the watertight test water pressure. But for Ling, bending, flattening test, weld most cracking. 
Peach tip: weld at no glitches, and recessed within the wall, forming the tip shape of peaches, try water pressure when water-tight. But bending, flattening test, weld multiple cracking. Within the burr unilateral: watertight seam burr for the side extrusion test water pressure. Bending, flattening test, sometimes cracking. 
Burnt: the outer surface of small pits in the weld, welding sparks a lot of splash, the microstructure observed small holes watertight when the test water pressure, bending, flattening test, most will not crack, but the impact on the intensity of use and life expectancy.
Weld defects 
Opening: straight weld plate edge face melting traces or melting traces without welding, crack two tip along the weld direction, expansion, penetrate the inner surface of the test water pressure, leaking. 
Crack: micro-crack crack; the outer surface of the visible appearance of fine lines, the inner surface of intact, no leakage in the test water pressure, but when crushed or cold-formed crack. 
Lap welding: two edge dislocation in the welding, scraping, except burrs can still see the obvious one side higher and exceed the wall thickness of the negative deviation.
Surface defects 
Scratch: the general was the axis of the straight channels and scratches, deeper than the wall thickness of the negative deviation of scrap defects in the weld on both sides of a continuous nail-shaped scratch. Super wall thickness of the negative deviation. Waste big flaw. 
Correction hurt: the leveler spiral crushed obviously feel more than the wall thickness of the negative bias of – waste defect. 
Pockmarked face: the tube surface successful piece punctate small pits with a diameter of about 1mm. 

Warp: the pipe surface warping the separation of the part and the metal substrate into pieces, not continuous, spalling can not afford.

ERW Steel Pipe Vs Seamless Steel Pipe
1. Comparison of wall thickness tolerance between erw steel pipe and seamless steel pipe
ERW steel pipe: hot-rolled coil is used as raw material, the thickness limit of modern hot-joining can be controlled within 0.05mm, and the seamless steel pipe is produced by round steel perforation, the wall thickness deviation is large, and the subsequent hot rolling can partially eliminate the wall. Thickness unevenness, but the current advanced unit can only be controlled within ±5~10%t, corresponding to the thickness of 8.94mm steel pipe.
Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.
2. ERW steel pipe and seamless steel pipe compared with outer diameter tolerance
ERW steel pipe: adopts cold-bending forming, and the sizing is completed by 0.6% reduction. The process temperature is basically constant at room temperature, so the outer diameter control is accurate and the fluctuation range is small, which is good for eliminating black leather buckle;
Seamless steel pipe: It adopts hot-rolling forming process, and its sizing is completed at 8000C. The raw material composition, cooling conditions and cooling state of the steel pipe have a great influence on the outer diameter, so the outer diameter control is difficult to be accurate and fluctuates. The range is large.
3. Comparative tensile test of erw steel pipe and seamless steel pipe
The tensile performance indexes of seamless steel tubes and erw steel tubes are in line with API standards, but the strength of seamless steel tubes is generally at the upper limit and the plasticity is at the lower limit. In comparison, the strength index of erw steel tubes is in an excellent state, and the plasticity index is higher than the standard 33.3%. The reason is that the performance of the raw material of the erw steel pipe-hot rolled coil is guaranteed by means of microalloying smelting, refining outside the furnace and controlled cooling and rolling; the seamless steel pipe mainly relies on the means of increasing the carbon content, and it is difficult to ensure the strength and plasticity. Reasonable match.
4. ERW steel pipe and seamless steel pipe compared ovality
ERW steel pipe: cold-formed, so the outer diameter control is accurate and the fluctuation range is small.
Seamless steel pipe: The hot rolling forming process, the raw material composition of the steel pipe, the cooling condition and the cooling state of the roll have a great influence on the outer diameter, so the outer diameter control is difficult to be accurate and the fluctuation range is large.

EFW pipe vs ERW pipe

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.

Electric Resistance Welding (ERW steel pipe): welding member combination is applying pressure through the electrodes, the use of current through the joint area of the contact surface and the adjacent heat generating resistance welding process method, Also known as contact welding. It has excellent toughness and dynamic load strength, welding deformation. 

Commonly used spot welding, seam welding and butt three.

Difference between ERW and DSAW pipe

Difference between ERW and DSAW pipe is generated in the carbon steel smelting defect smelting and casting process, such as segregation, non-metallic inclusions, porosity, shrinkage and cracks.

Double Submerged Arc Welded (DSAW) steel pipe

Double Submerged Arc Welded (DSAW) steel pipe is available in straight and spiral welded formats and used in a variety of applications. The submerged welding process protects the steel from contamination of impurities in the air. Both inside and outside welds are performed.

SEGREGATION

Segregation is the uneven distribution of chemical composition in the steel, in particular harmful elements such as sulfur, phosphorus enrichment in the ingot.

NON-METALLIC INCLUSIONS

Non-metallic inclusions refers to non-metallic inclusions in steel containing impurities such as sulfides and oxides.

STOMATA

Stomata refers iron and carbon monoxide gas effect generated in the pouring can not fully escape and stay in the tiny pores in the ingot.

SHRINKAGE

Shrinkage is due to the liquid steel ingot mold from outside to inside, the volume contraction during solidification bottom-up, because the level drops, the final solidification of liquid steel parts can not be added to form. 

CRACK

Solidification of liquid steel in the order due to different causes stress, tension cracks may appear larger parts.

High frequency straight seam welding (ERW) method is divided into two forms of induction welding and contact welding, hot-rolled wide volume as raw material, pre-curved, continuous molding, welding, heat treatment, sizing, straightening, cutting, etc. process, compared with the spiral weld short, high dimensional accuracy, uniform thickness, surface quality, pressure advantages, but the drawback is that only the production of small and medium-caliber thin-walled tube, weld easy to produce gray leaf spot, not fusion ditch-like corrosion defects. Wider application areas of city gas, crude oil transportation.

Spiral submerged arc welding (SSAW)

Spiral submerged arc welding as raw material is often warm extrusion molding, automatic double -sided wire submerged arc welding process.

The process is normally limited to the flat or horizontal-fillet welding positions (although horizontal groove position welds have been done with a special arrangement to support the flux).

SPIRAL SUBMERGED ARC WELDING PROCESS PERFORMANCE:

(1) raw materials that strip, wire, flux. Must go through rigorous testing before being put into the physical and chemical.
(2) strip head and tail docking, using single or double wire submerged arc welding, in rolled steel by automatic submerged arc welding.
(3) Before molding, the strip after flattening, cutting, trimming, planing, surface cleaning and transportation to the curved edge treatment. 
(4) the use of electrical contacts on both sides of the conveyor control the pressure cylinder pressure to ensure the smooth delivery of the strip. 
(5) the use of internal or external control roll forming. 
(6) the weld gap control device to ensure that the weld gap to meet the welding requirements, diameter, volume and the wrong side of the weld gap have been strictly controlled. 
(7) the welding and soldering are used outside the United States Lincoln welding machine for single or double wire submerged arc welding, to obtain stable welding specifications. 
(8) After welding the weld line continuous ultrasonic injury checked to ensure 100% coverage of non-destructive testing of spiral weld. If defective, automatic alarm and spraying tags, production workers so adjusting the process parameters, and remove defects. 
(9) the use of air plasma cutting machine to cut a single tube. 
(10) cut into a single pipe, the first three of each batch of steel to carry out strict inspection system, inspection of weld mechanical properties, chemical composition, fusion status, steel surface quality and after NDT inspection to ensure that the process pipe after passing to formally put into production. 
(11) there is a continuous sonic flaw marks the site of the weld, manual ultrasonic and X-ray review, if there are defects after repair again after destructive testing until confirmation defect has been eliminated. 
(12) strip on the spiral weld seam and intersects with D-type connector where the pipe all through the X -ray television or film examination. 
(13) each pipe hydrostatic test pressure radial seal. Test pressure steel pipe pressure and time by computer testing device strictly controlled. Test parameters are automatically printed record. 
(14) pipe end machining, so that the end vertical, blunt edge bevel and accurate control.

SSAW pipe is its forward direction and forming tube centerline hose reel molding angle (adjustable), side molding edge welding and weld them into a spiral.

Spiral submerged arc (SSAW) is its forward direction and forming tube centerline hose reel molding angle (adjustable), side molding edge welding and weld them into a spiral, the advantage of the same specification to produce a variety of diameter sizes steel pipe, raw materials to adapt to a wider range, the weld can avoid the main stress force better, the disadvantage is the poor geometry of the weld length compared to the long straight seam pipe, prone to cracking, porosity, slag, welding partial welding defects such as welding stress was tensile stress state. General Oil and Gas Pipeline design specification spiral submerged arc can only be used for Class 3, Class 4 regional. Raw materials instead will this process improvement abroad steel plate forming and welding separate pre-weld and lean and, after welding cold flaring near UOE pipe welding quality, currently no such process of plant improvement direction. “West-East” still is a traditional craft production, just expanded diameter of the pipe end. United States, Japan and Germany, the overall negative SSAW, think the mainline unfit for use SSAW; Canada and Italy part SSAW Russian small amount of SSAW, and have developed a very strict supplementary conditions, due to historical reasons, the majority of the domestic main trunk or use SSAW.

Longitudinally Submerged Arc Welded Steel pipes

Longitudinally Submerged Arc Welded Steel pipes list

Range of LSAW pipes applied in construction: Outer diameter: Ф350-1600mm, Wall thickness: 6-60mm, Unit length: 6-12m.

LSAW pipes are mainly used as long distance transportation pipeline for oil, gas, liquid coal etc. on land and offshore. 
And also can be applied as construction pipes on offshore platform, power station, petrochemistry and city construction etc.

LSAW in leaflets plate as raw material, the steel plate in the mold or molding machine pressure (volume) into using double-sided submerged arc welding and flaring from production. A wide range of the finished product specifications, weld toughness, ductility, uniformity and dense, with a large diameter, wall thickness, high pressure resistance, low-temperature corrosion resistance, etc.. Required steel pipe in the construction of high-strength, high toughness, high-quality long-distance oil and gas pipelines, mostly large diameter thick wall LSAW.

API standard provisions, in the large-scale oil and gas pipelines, when 1, Class 2 areas through the alpine zone, the bottom of the sea, the city densely populated area, LSAW only applied specifically casts. Molding can be divided into:

UOE: leaflets steel plate after the edge preflex, after U molding, O forming within welding, the outer welding, mechanical cold expanded diameter process;

JCOE: Press “JCOE” pre-welding, forming, welding after cold expanded diameter process;

The Application of ERW Steel Pipe in Oil and Chemical Industry
In recent years, there has been a trend in the world to replace high-cost seamless steel pipes with high-quality welded pipes. This is mainly due to the continuous breakthrough in the production technology of welded pipes, which is reflected in the following aspects:
(1) Advances in desulfurization technology have reduced the sulfur content of steel and improved the welding quality of steel pipes.
(2) The application of vacuum degassing technology improves the purity of the tube blank strip, reduces inclusions, and improves the quality of the weld.
(3) Due to the addition of special elements such as V, Ti, and Nb, the carbon equivalent is lowered, and the toughness and strength of the steel pipe are improved.
(4) The development of hot rolling technology has improved the dimensional accuracy of the strip and thus reduced the dimensional deviation of the welded pipe.
(5) Improvement of quality inspection methods, such as ultrasonic non-destructive testing, hydraulic testing machines and other equipment, to ensure the quality of the final product.
Steel pipes selected by petrochemical enterprises generally use seamless steel pipes for fluid transportation because they have to withstand certain pressures. In 1996, during the “National Ninth Five-Year Plan” key construction project “Maoming 300,000 t ethylene project”, the “Mushui Product Oil Pipeline Relocation Project” and the “Second Maoshui Product Oil Pipeline Project” long-distance transmission process part required 325mm× 8mm, 168mm × 7mm, 219mm × 7mm steel pipe, mainly used for the transportation of gasoline, diesel, kerosene, etc.
China’s erw steel pipe industry started in the 1950s and started late. The production process and technology are quite different from those in developed countries. Most of the enterprises have incomplete process and equipment, lack of necessary testing methods, and use short-band and narrow-band materials with poor quality as raw materials, resulting in small diameter of the welded pipe products, low pressure bearing capacity, unreasonable product structure, and 80% of the welded pipe production. It can be used as a low-pressure fluid conveying water gas pipe, and the proportion of various special pipes is low. This low level of welded pipe equipment and technical level makes the quality of the product unguaranteed. Therefore, long-term use of expensive seamless steel pipes such as pipeline pipes, oil casings and oil pipes causes huge waste.
Some technical performances of erw steel pipe are better than seamless steel pipes, but the price is much lower than that of seamless steel pipes, but it has not been widely used in the petrochemical industry. The main reasons are:
(1) The traditional concept that has been formed for a long time. When selecting materials, designers mainly consider whether the material is reliable and rarely consider the cost of materials. Therefore, it is not possible to boldly use erw steel pipes.
(2) The investment system of petrochemical enterprise construction projects restricts the initiative to select erw steel pipes and reduce costs. Investors mainly consider the project’s project establishment, funding sources, construction progress and other factors, and less demand for designers to reduce material costs.
(3) China’s straight seam electric resistance welded steel pipe developed late, and it is not yet possible to produce large diameter straight seam welded pipe larger than 508mm, thus objectively restricting the wide use of erw steel pipe.
Notes of ERW Steel Pipe When Testing Water Pressure
When the hydraulic test of the erw steel pipe is carried out, it is often found that the bursting opening is cracked from the weld of the erw steel pipe, which indicates that the strength of the welded portion is lower than that of the base metal. Through experimental analysis, it is found that if an internal scraping groove is formed on the inner surface of the steel pipe during the removal of the burr in the weld, the wall thickness of the sample at the weld bead is reduced, and the sample is easily broken from the tensile test. 
The water pressure test of the water supply pipeline is the means for the final quality assessment of the erw steel pipe laying. Generally, there are two main requirements for the hydraulic pressure test: one is that it can correctly reflect the leakage of the pipeline; the other is the pressure test. No problem, nor can the interface be damaged due to pressure test, but it will affect the quality of the project, or retry the work, resulting in waste, and can not cause personal safety accidents.
In addition, when the weld tensile test is carried out in accordance with APISPEC 5L, it is often the case that the remaining height of the weld is removed or retained, and the weld is often broken. This indicates that the strength of the weld of the erw steel pipe is lower than that of the base metal. There are two reasons for the analysis: one is that the strength of the weld portion of the erw steel pipe is lower than that of the base material; the other is the scraping on the inner surface of the steel pipe when the burr in the weld is removed. The groove or the residual burr causes the transition of the weld portion and the base material to be unreasonable, resulting in stress concentration, so that the overall structural strength of the weld portion is lower than that of the base material portion. Therefore, the transition shape of the weld portion of the ERW welded pipe and the base metal should be optimized to ensure the overall quality of the steel pipe. The hydraulic pressure test is not necessarily 1.5 times of the design pressure. For details, please refer to GB50235-2011 Industrial Metal Pipeline Construction Specification or TSG-D0001 Pressure Pipe Safety Technology Supervision Regulations – Pressure Pipeline Standard.

Source: China ERW 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.)