What is DSAW steel pipe?

What is DSAW steel pipe?
DSAW steel pipe can be specified in very large diameter and to exact inside or outside dimensions.

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. 

electric resistance welding at a glance forge welding process diagram - What is DSAW steel pipe?

Welding advantages of double submerged arc welded straight seam steel pipe
Double submerged arc welded straight seam steel pipe is a new welding method invented in 1940, it is the same place and the front of the manual welding it or slag protection, but this residue is not the electrode coating, but melting out welding flux. Flux system consists of a funnel filled with flux transported through a pipeline to the front to be welded. The second difference is not electrode, wire, because the wire can be continuously sent to; electrode, we burn an electrode must have a welding rod head gave throw, and the operation is stopped, and then change electrode welding. After the wire is changed, with a means to send the wire and the wire for rent, gave continuous welding wire, welding wire is continuously fed, covered with a granular flux can be melted under the ignition of the arc, the welding wire, base material and part of the melting and evaporation of the flux constitute a cavity arc inside the cavity stable combustion, it called submerged arc welding. The arc is buried in the cavity inside. 
The advantages of the double submerged arc welded

  • First: it is completely automated.
  • Second: it is carried out under the submerged arc welding, the heat exchange and protection performance is relatively strong, relatively high welding quality;
  • Third: submerged arc welding arc buried under the flux, so it can be used high current, high welding efficiency, the ongoing West-East Gas Pipeline project in our country recently.

Pipe is a high-strength steel, this first prefabricated section of pipe at the factory inside, and then get on the site, field welding, the welding process is the use of this pipeline in the factory to make a submerged arc welding, submerged arc welding has developed into a double wire submerged arc welding, as well as multi-wire submerged arc welding, to further improve the efficiency.

DSAW steel pipe production process:

I. double submerged arc welding process, the plate deformation uniformly small, residual stress, surface does not produce scratches. Processing of pipe diameter and wall thickness of the pipe sizes range, greater flexibility, especially in the production of high-grade steel thick-walled steel pipe, large diameter thick wall pipe has the incomparable advantage of other technology, to meet the users in pipe size requirements;

Ⅱ. Presoldering outside welding (the fine welding) the process can be implemented in the best position welding, less prone to the wrong side of the welding partial and incomplete penetration defects such as welding quality, easy to control;

Ⅲ. Overall mechanical enlarged diameter, which can effectively improve the dimensional accuracy of a steel pipe, and improve the distribution state of the stresses in the steel pipe, thus avoiding the damage caused due to stress corrosion, is also conducive to the welded construction of the scene;

Ⅳ. 100% quality check on the steel, so that the whole process of pipe production are effective detection, monitored, to ensure the product quality of the SAW pipe;

Ⅴ. Entire production line equipment have networked with a computer data acquisition system to realize the real-time transmission of data, the quality of the technology in the production process parameters and quality indicators adopted by the central control room.

Based on strip coil as raw material and often warm extrusion using automatic double wire two-sided submerged arc welding process. Raw material has strip volume, the welding wire and flux. going through rigorous physical and chemical testing before input. Strip head and tail docking, using a single wire or twin-wire submerged arc welding and automatic submerged arc welding rolled into the steel pipe. Prior to molding, strip is through flattening, cutting, trimming, edge planing, transportation and to the curved side surface cleaning.

Double submerged arc welded pipe (DSAW) derives its name from the welding process wherein the welding arc is submerged in flux while the welding takes place. Both inside and outside welds are required and are usually accomplished in separate processes, hence the word “double.” These separate welds consume a portion of the other resulting in a single high quality weld nugget.
 DSAW pipe is produced in sizes from 18″ through 72″ 00 and wall thicknesses from .250″ through 1.5″.
Two different processes are used to manufacture DSAW pipe; the pyramid rolls method, and the U-O-E method. The difference in the processes is found only in the method of forming the cylinder. In the pyramid rolls process the cylinder is formed between 3 rolls arranged in a pyramidal fashion. As the name implies; the U-O-E method uses a “U” press, and “0” press for forming. Other parts of the process such as finishing and inspection are similar. Both processes use flat steel plate as the raw material. 
DSAW pipe mayor may not be cold expanded. Cold expansion is a process where the pipe is expanded (up to 1_5%) to obtain its final 00 dimension. In the process, a gain of yield strength results. Expansion is most often utilized in a U-O-E mill due to the need to recover the yield strength lost during forming in the “0 press, DSAW pipe is available in the following grades: 
ASTM A134, A139, A252, A671, A672, A690, A691, CSA (Canadian) – Z245.1 and custom specifications. API 2B, 5LB, 5LX-42 thru 5LX-80
DSAW pipe is normally produced in double random lengths with square ends or beveled for welding. It is usually furnished bare but varnish is also offered. A wide range of external coatings and internal linings are available with DSAW pipe. These include fushion bond epoxy (FBE) coatings and thin film epoxy linings. DSAW pipe is used in high pressure gas and oil transmission lines (both onshore and offshore), structural members and pipe piles. Major purchasers include liquid and gas transmission companies, hammer companies, construction contractors, platform fabricators, government agencies and pipe distributors.

Advantages of DSAW Pipe
DSAW pipe is made of steel plate as raw material, and is often extruded by automatic double-wire double-sided submerged arc welding process. DSAW pipe is simple, high efficiency and low cost. In the steel pipe forming steel plate deformation evenly, the residual stress is small, does not appear to scratch the surface of the phenomenon. In the diameter and thickness of the steel pipe size specifications can be used flexibly in the production of large diameter thick seam steel pipe advantage is more obvious. In the production process can be pre-welded after welding inside and outside, to ensure that welding does not appear wrong side, welding bias and not penetration and other defects, the quality of welding control easier.
Advantages of dsaw pipe is more obvious. In the production process can be pre-welded after welding inside and outside, to ensure that welding does not appear wrong side, welding bias and not penetration and other defects, the quality of welding control easier.
Details advantages of dsaw pipe:
The first advantage is the full realization of automation;
The second advantage, it is under the submerged arc welding, so its heat exchange and protection performance is relatively strong, welding quality is relatively high;
The third advantage, due to submerged arc welding in the arc buried under the welding, so it can use high current, welding efficiency is relatively high, recently our country is ongoing West-East Pipeline project.
Into the welding wire, with the welding device and the wire, continuous feeding to the welding wire, this welding method is continuous feeding of the wire, in the melting of the granular flux covered by the arc, so that welding wire, and a part of the flux melting and evaporation constitute a cavity, the arc is stable inside the cavity burning, so it is called submerged arc welding. 
Inside the cavity. Pipeline is a high-strength steel, this pipe in the factory first pre-made into a section, and then get the site, in the field of welding, this pipe factory in the welding process is the use of submerged arc welding, submerged arc welding has developed into a double wire submerged arc welding, as well as multi-wire submerged arc welding, the efficiency is further improved.
Difference between ERW and DSAW pipes

Difference between ERW and DSAW pipes 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 pipe banner - What is DSAW steel pipe?
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.

Difference between HFW and DSAW

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

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.

erw pipe banner - What is DSAW steel pipe?
ERW pipes means Electric Resistance Welded Pipes.

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 DSAW 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.

Kind for welding pipe
Welded pipe is generally divided into straight seam welded pipe and spiral welded pipe two types.
Welding process
From the welding process, Welding method of the spiral welded pipe and straight seam steel pipe is consistent, but the straight seam welded pipe will inevitably have a lot of t-shaped weld, so the probability of weld defects is also greatly improved, and the t-shaped seam welding residual stress is larger, the stress state of the weld metal are often in a three-way increases the possibility of a crack.And, according to the regulations of submerged arc welding process, each weld shall have arc and arc in, but every straight seam welded pipe when weld girth, can not meet the conditions, thus there may be more at arc welding defects.

  • ERW pipes- A plate rolled to become a pipe and welded using Electric Resistance Welding process.
  • (HFI) High frequency welded pipe- 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.
  • (EFW) Electric Fusion Welded Pipe- The EFW pipe divison consists of a JCO forming press, helical / spiral mill, inside and outside welding system, heat treatment furnace and testing facilities.
  • (LSAW) Long-Submerge-arc Welded – 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.
  • (DSAW) Double Submerged Arc Welded- is available in straight and spiral welded formats and used in a variety of applications.
  • (UOE) Uing and Oing forming pipe- the formed pipes are welded inside by five internal welding stations with three wires for each weld,and welded outside by four external welding stations with three wires for each weld.
  • (JCOE) J-ing, C-ing and O-ing- process with characteristics of high forming accuracy and efficiency as well as balanced distribution of forming stress.
  • (SSAW) Spiral submerged-arc welding- is its forward direction and forming tube centerline hose reel molding angle (adjustable), side molding edge welding and weld them into a spiral.
  • (SAW) Submerged arc welding pipe- is a common arc welding process.

Strength characteristics
When the pressure in the pipe withstand, usually two main stress on the wall, that the radial and axial stress stress δ. Synthetic weld stress δ, where α is the helix angle of the spiral weld pipe. Spiral welded seam degree helix angle is generally so synthetic, and spiral weld Longitudinal stress is the main stress. Under the same operating pressure, spiral pipe of the same diameter than the Longitudinal wall thickness can be reduced.
Hydrostatic burst strength
By the relevant comparison test to verify the spiral welded pipe and Longitudinal yield pressure and burst pressure measured and theoretical values match, the deviation closer. But whether it is the yield stress or burst pressure, were lower than the Longitudinal spiral welded. Burst test also shows that the rate of deformation ring spiral welded pipe bursting Longitudinal significantly greater than the mouth. Thus confirmed that the spiral welded plastic deformation capability than Longitudinal, blasting mouth generally confined to a pitch, which is the extension of the spiral weld to rip from a strong binding effect due.
Toughness and fatigue strength
The trend of the development of the pipeline is of large diameter and high strength. With the increase of the diameter of the pipe and the steel grade increases, the greater the ductile fracture tip steady expansion trend. Although spiral welded pipe and straight seam welded pipe has the same level, spiral welded pipe is with high impact toughness. Transmission pipelines due to the amount of change in the actual operation, the pipe is subjected to random alternating load effect.

Source: China Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.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@steeljrv.com

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References:

  • https://www.yaang.com

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