A welded steel pipe is constructed from a flat steel plate or a flat steel strip, and the manufacturing process results in a seam on the pipe’s surface. For welded steel pipes, the steel plate or strip must be bent and then welded into either a circular, traditional pipe shape or a square shape as part of the manufacturing process. There are three types of welded steel pipes: LSAW pipe, SSAW pipe, and ERW pipe. Each type is categorized based on the way in which the pipe is welded. There are two types of welding techniques used in pipes, LSAW and SSAW. LSAW pipes are longitudinally welded, while SSAW pipes are spirally welded. ERW pipes are electric resistance welded, which results in a seam that runs parallel to the pipe body.

There are many types of welded steel pipe, but all of them are quick and easy to produce. Moreover, they tend to be cheaper than their alternatives, such as seamless steel pipe, which occupies more space and costs you more money. Overall, welded stainless steel pipe is an affordable, adaptable material that can be used for a wide variety of projects.

As the name suggests, welded pipe (i.e. pipe that is manufactured with a weld) is a tubular product that is manufactured from flat plates called skelps, which are formed, bent and prepared for welding, with a longitudinal seam weld being the most common method for large diameter pipes.

A spiral welding process is an alternative method for making pipe with large diameters from narrower plates or skelps, as well as using spiral welding as a construction method. As with longitudinally welded SAW pipe, spiral welded pipe joint may also experience defects associated with the SAW weld. This defect is similar to the defects experienced by longitudinally welded SAW pipe in its nature.

A high frequency induction (HFI) is a welding process that produces electrical resistance weld (ERW) and high frequency induction (ERW) pipe. Originally, this type of pipe was manufactured by resistance heating to make the longitudinal weld (ERW), which is composed of a solid phase butt weld. Although the majority of pipe mills now use high frequency induction heating (HFI) in order to improve quality control and consistency, the product is still commonly referred to as ERW pipe, even though the weld may have been produced using the HFI/HFW (High Frequency Welded Pipe) method.

During the manufacturing process of welding pipes, a plate or coil is either rolled in a circular section using a plate bending machine or by a roller in case of the continuous process process. This is done with the help of the plate bending machine. It is possible to weld the circular section of the pipe with or without filler material once the circular section has been rolled from the plate. This type of pipe can be manufactured in large diameters without any upper limit on size. A welded pipe filled with filler material can be used for the manufacture of long radius bends and elbows with a wide radius. Compared to rolled and welded pipes, welded pipes are cheaper than seamless pipe, but they are also weaker than seam welded pipe since they have a weld joint at each end. A welded pipeline can be manufactured in large sizes without any restriction on their size.

Properties of Welded Steel Pipe

As well as offering many of the properties associated with steel, it also offers a number of other benefits that can be used to the advantage of buried pipelines in addition to its properties. The following are the desirable characteristics of buried, pressurized pipe. Welded steel pipe can meet these criteria.

• Strength – 

The steel pipe has a high level of strength and stiffness (modulus of elasticity).

• Ease of installation – 

The lightweight and toughness of steel pipe make it ideal for transportation and installation, as it can withstand forces, deformations, and impacts that would otherwise fracture brittle materials.

• High-flow capacity – 

Steel pipes have a relatively low frictional resistance to flow.

• Leak resistance – 

There is a requirement that all underground pipes must be designed, whether it is the pipe itself or the soil embedment. Welded joints are leak-proof. Gasketed joints are designed to be leak-proof and bottle-tight within the recommended limits of pressure and angles between the adjacent pipe sections.

• Long service life – 

There are buried pipes in our civil engineering infrastructure that are the “guts” of our growing demand for supply services. Steel pipes will be an important part of the world’s infrastructure in the coming decades. The service life of steel pipe is greatly influenced by the rate at which it becomes corroded externally and abraded internally.

• Reliability and versatility – 

In addition to its strength (ductility), steel pipes are very versatile due to their ductility and their ease of cutting and welding processes. They can be tailored to meet virtually any requirement due to their ductility and their flexibility. There are virtually no limits to the size or strength of steel pipes.

• Economy – 

The final cost of buried pipe includes: the pipe, embedding, transportation, installation, operation, maintenance, repair, modification and risk. Over its design life, steel pipe is cost effective. A steel pipe is transportable and lightweight because of its thin wall and light weight, so it is relatively cost efficient, especially when it has a large diameter. (Requirements for blocks and stulls are minimal.) Due to its lightweight, steel pipe can be installed quickly. In the event of damage to steel pipes, they can often be repaired on site in the case of damage to the pipes. The longer the pipe section, the less welds there will be (or the fewer bell and spigot joints that will require gasketing and stabbing). Welded steel pipe sections are generally able to hold together in the event of a massive soil washout and minimize the disaster caused by a break in a pipeline during a massive soil washout.

Joints

There are many types of joints for joining steel pipe lengths in the field. The most commonly used joints include:

• Rubber gaskets on bell and spigot joints –

Suitable for working pressures up to 250 psi (1,723.7 kPa) and pipe diameters up to 72 inches (1.82 meters), and wall thicknesses up to 3/8-inch (9.52 mm), these valves can be used. There is some angular deflection (flexibility) at the joint with this type of joint, and it is the easiest to install. A supplemental restraint or anchoring must be considered at all points of longitudinal thrust when using this type of joint. This type of joint is covered by the AWWA C200 Standard.

• Welded lap joints – 

The valves can be used for all diameter pipes up to a working pressure of 400 psi (2,757.9 kPa) and sometimes even higher. A joint of this type allows for some angular deflection during construction, as well as having the ability to be assembled rapidly in the field, saving considerable amounts of money compared to butt-welded joints, as the joint can be welded only on the outside or, if the size can safely be entered, on the inside. There are some special circumstances in which it will be desirable to weld both inside and outside the joint, as well as to perform an air test on the joint. There is an AWWA C200 standard which covers requirements for welding this type of joint, and an AWWA C206 standard which covers welding this type of joint in the field.

• Welded butt joints – 

There are many types of joints that are suggested when working pressures exceed 400 pounds per square inch (2,757.9 kPa) as these joints are not suitable for angular deflection except for miter cuts made on both pipes ends, so they can only be used for working pressures over 400 pounds per square foot. A pipe can be deflected by up to 5 degrees if one end of the pipe is mitered and up to 10 degrees when both ends are equally mitered. This type of joint is difficult to fit, so it is typically made easier by using line-up clamps or welded to one end of the pipe for the line-up. A For this joint, a full-penetration groove weld is required. The AWWA C200 Standard addresses the requirements for this type of joint, and the AWWA C206 Standard addresses the requirements for field welding in this type of joint.

• Butt-strap joints – 

This strap is used for closing or regulating the temperature in butt-welded lines. The strap can either be shipped loose in one or two sections that require a longitudinal field weld or it can be welded to the end of one pipe by a shop welder. It should, however, be welded inside and out in certain conditions. If so, tapped holes can be provided to allow for an air test according to the AWWA C206 Standard.

• Mechanical couplings – 

The AWWA C219 Standard covers sleeve-type couplings for pipelines of all diameters and pressures. There has been a thorough technical description of the requirements for sleeve-type couplings published in that standard. Mechanical couplings are extremely flexible and strong. A pipeline is relieved of expansion and contraction forces by these structures, providing enough flexibility for the pipe to be laid over long radius curves and grades without the need for special equipment. There are rubber gaskets that are firmly held between the coupling parts and the pipe, and these gaskets ensure that they are held securely against any internal pressure conditions, including vacuum conditions, during the assembly. There is no risk of damage or decay to the rubber gaskets, as they are completely enclosed. The use of these joints has been successful since 1891 when they were first introduced. In durable, flexible, solid-sleeve couplings, an acceptable amount of axial movement is 3/8-inch (9.52 mm) which is a result of shear displacement of the rubber gaskets rather than sliding off the gaskets on the mating surface of the pipe and is derived from the shear displacement of the rubber gaskets. Rather than using mechanical couplings for a longer distance, it would be best if they could be replaced with true expansion joints. It is important to note that unrestrained mechanical couplings transmit only minor tension or shear stresses across pipe joints, and when used alone, they cannot allow differential settlement at these joints if the coupling is not used. Nevertheless, there is the possibility for flexibility when another flexible joint is adjacent to it.

• Split-sleeve couplings – 

Couplings made of a solid sleeve are often used in place of solid sleeve couplings. As a result of split-sleeve couplings, the pipe can be out of round (barrel deflection), joints can be restrained completely, the pipe can expand and contract beyond 3/8 inch (9.52 mm), and many other common (or rare) field conditions can be accommodated. As specified by the American Water Works Association, AWWA C227 is the standard governing the quality of materials and performance of split-sleeve couplings.

• Flanged joints –

 Flanged joints are commonly used for connecting valves or other appurtenances. It is not common to use flanges on large-diameter pipes, since they are difficult to install, due to their large diameter high cost, and lack of flexibility. Standard flanges have advantages, however, for special connections, such as bridge crossings, long spans, or other rigid joints.

Welded Steel Pipe Applications

As we have shared with you in our introduction, welded steel pipe has many applications. In the following paragraphs, we have listed a few of the most common applications for this kind of steel pipe.

• Water and Gas Transport

Besides being an excellent transporter of water, other fluids, and natural gas, welded steel pipe is also an excellent choice when it comes to large-scale projects because of its cost-effectiveness.

• Pipe Casing

It is usually necessary during the construction of drill shafts to make use of pipe casing for support while the drilling is taking place, which can be made out of welded steel pipe. A temporary or permanent pipe casing can withstand the type of operation being undertaken.

• Bearing Piles

When used as a bearing pile, larger, heavy structures are able to be supported and carried by welded steel pipe driven deep into the ground as bearing piles. To reinforce the piles, welded steel pipes can be filled with concrete to increase their strength.

• Combi Walls

It is possible to use welded steel pipe in the construction of combi walls, which are used as retaining structures and in several cases are utilized along with steel sheet piles to create a sturdy, long-lasting structure that is able to support massive loads. The pipe can be used in conjunction with steel sheet piles to create strong and durable structures.

• Underground Utilities

Underground utilities can be installed with bore and jack-welded steel pipe. In this process, hydraulic jacks are used to drive sections of steel pipe between excavations, which are then joined with other sections of spliced pipe. The pipe structure is cleared and cleaned out once it has been constructed so utility work can be conducted in a safe environment.

• Structural Sections

It is possible to create large, open structures using welded steel pipe, such as cofferdams, when it is used in conjunction with other materials. By using it in this way, it is capable of offering equal bending resistance in every direction, which means that when substantial loads are being supported over substantial lengths, it will remain resilient to buckling.

In terms of cost-efficiency as well as overall efficiency, you may find that you use welded steel pipe in a variety of applications. As a result, welded steel pipe is an excellent and reliable choice in terms of both cost-effectiveness and overall efficiency.