Based on the method of manufacturing, pipes are classified as either seamless or Welded pipes, according to the way they are constructed. A seamless pipe is formed at one point during the rolling process, while a seamed pipe has to undergo a welding process after it has been rolled. In accordance with the geometry of the seam, seamed pipes can be classified into two categories in terms of their seam geometry: spiral welding and straight welding. While there is debate over whether seamless steel pipes are better than seamed steel pipes, either seamless or welded steel pipe manufacturers are able to produce steel pipes that can provide high quality, reliability, and corrosion resistance. A major factor that should be considered when deciding which pipe type to use is the specification of the application and the cost implications.
Seamless PipesAll You Need to Know About Stainless Steel 304 Welded Pipes
It is generally the case that seamless pipes are made in a number of complex steps, beginning with drilling hollows from billets, followed by cold drawing and cold rolling processes. There is a great deal of difficulty in controlling the outside diameter and wall thickness of seamless-type tubes compared to welded tubes, so cold work can improve the mechanical properties and tolerances of the tubes. I believe that one of the greatest advantages of seamless pipes is that they can be produced in heavy and thick wall thicknesses, which is one of their biggest advantages. Having no weld seam allows them to be considered as having better mechanical properties and corrosion resistance than seamed pipes because of the fact that they have no weld seam. Seamless pipes are also expected to have a better ovality or roundness in comparison with conventional pipes. As a general rule, they are preferred to be used under extreme environmental conditions, such as high loading, high pressure, and highly corrosive conditions.
In order to form a welded steel pipe, a steel plate is rolled into a tubular shape through the use of a seam or spiral seam to form the shape of the pipe. Welded pipes can be manufactured in a number of ways, depending on the outer dimension, the wall thickness, and the application they will be used for. A hot steel billet or a flat strip is used for each method, which is then used to make a pipe, which is made by stretching the hot steel billet, forcing the edges to come together, and then welding them together. The wall thickness of welded pipes is thinner than that of seamless pipes due to tighter tolerances, as compared with seamless pipes. Seamed pipes are also considered to be more cost-effective and may be more convenient to use than seamless pipes due to their shorter lead time and lower cost. Although the weld seam may be a sensitive area that can facilitate crack propagation and cause the pipe to fracture, it is important to control the surface finishing of the outside and inside of the pipe during production.
It is important to emphasize that both manufacturing methods involve the raw steel first being cast into a form that allows it to be easily worked (hot billets or flat strips). The hot steel billet is then stretched out into a seamless pipe or the edges of the flat steel strip are forced together and sealed with a weld to essentially form a pipe out of the steel billet.
Welded Pipe Manufacturing
In order to manufacture seamless pipes, plates, coils, or strips of metal can be used. In order to manufacture a seamed pipe, the first plate or coil is rolled into the circular section of the pipe using a plate bending machine or a roller if the process is continuous in order to create a circular section. The circular section can be either welded with or without filler material when it is rolled from the plate and then attached to the pipe. The pipe can be welded in a variety of different ways by using different welding methods.
Electric Resistance Welding Process (ERW)
A flat sheet of steel is cold-formed into a cylindrical shape using the electric resistance welding process. A current is then passed through the edges of the steel cylinder to heat up the steel and form a bond between the edges of the cylinder at a point where they are forced to meet in order for the bond to form. There are also times when filler materials may be used during ERW processes. High-frequency welding is one type of electric resistance welding, and rotary contact wheel welding is the other type.
High-frequency welding is becoming increasingly necessary due to the fact that low-frequency welding products are prone to selective seam corrosion, hook cracks, and inadequate seam bonding, which has led to the need for high-frequency welding products. It is therefore no longer possible to manufacture pipes using low-frequency ERW technology. Pipes are still being manufactured using the high-frequency ERW process in the pipe manufacturing industry. As far as high-frequency ERW processes are concerned, there are two types to choose from. One type of high-frequency welding is high-frequency induction welding, while the other type is high-frequency contact welding. The high-frequency induction welding process involves a coil that transmits the weld current from the welder to the material to be welded. In this case, the coil does not come into contact with the pipe. As a result of magnetic fields surrounding the pipe material, an electrical current is induced into it, causing it to conduct electricity. Contact welding involves the transmission of current to the material by means of contacts that ride on the strip as the current passes through it. Since the welding power is applied directly to the pipe, it makes the welding process more efficient, since it directs the power to the pipe, which produces a more efficient welding process. In general, this method is preferred for producing pipes with a large diameter and a high wall thickness.
This type of welding process is also referred to as electric resistance welding, and it is a type of rotary contact wheel welding. In this process, an electrical current is transmitted through the weld point through a contact wheel that transmits the current. The contact wheel is also responsible for applying the necessary pressure for the welding process to take place. When an impeder cannot be accommodated inside of the pipe, rotary contact welding is generally used for applications where an impeder cannot be used.
Electric Fusion Welding Process (EFW)
A steel plate can be welded by an electron beam welding process using the high-speed movement of the electron beam. During the welding process, the high kinetic energy of the electron beam is converted into heat to produce the weld seam on the workpiece. Heat treatment can also be applied to the welding zone in order to make the weld invisible in order to make the weld as invisible as possible. In general, welded tubes have tighter dimensional tolerances than seamless tubes, and they are more cost-effective if they are manufactured in the same quantity as seamless tubes. As a metal welding process, it is mostly used for welding dissimilar steel sheets together or for welding parts with high power density. With this process, metal welding parts can be heated to high temperatures quickly, melting refractory metals and alloys.
Submerged Arc Welding Process (SAW)
It is a welding process in which an arc is formed between a wire electrode and the workpiece during submerged arc welding. For the generation of protective gases and slag, a flux is used as fuel. As the arc moves along the joint line, excess flux is removed through a hopper as the arc moves along it. The arc is usually not visible during welding as it is completely covered by the flux layer, which also makes it extremely low in terms of heat loss, as the arc is fully covered by the flux layer. Submerged arc welding processes are divided into longitudinal submerged arc welding and spiral submerged arc welding.
The longitudinal edge of a steel plate is first beveled with the aid of milling to form a U shape before it is submerged in arc welding. Afterward, the edges of the U-shaped plates are welded together. During the process of manufacturing pipes, they are subjected to an expanding operation, which is meant to relieve internal stresses and to achieve a perfect tolerance in the dimensions of the pipes.
In spiral submerged arc welding, the weld seams encircle the pipe in a helix-like pattern as the weld is being arc welded. There is no difference in the technology used for longitudinal and spiral welding as both methods utilize the same technology. The only difference between the two methods is the spiral shape of the seams in spiral welding. Rolling the steel strip, so that it is at an angle to the direction of the pipe center, forming the pipe, and welding it, so that the welding seam is in a spiral line, is the manufacturing process, which includes rolling the steel strip and making the rolling direction angle to the pipe center. The major disadvantage of this process is the poor physical dimensions of the pipes as well as the long seam lengths, which could easily result in a defect or crack forming as a result of the process.
In order to ensure that the steel pipe that is finished meets the specifications, a variety of measures are taken. The thickness of the steel is regulated with the help of x-ray gauges, for example. There are two x-rays that are used in the gauges in order to measure the density. There is a ray that is directed at a steel plate of known thickness that is in the beam. One is directed at the passing steel on the production line, while the other is directed at the passing steel. The gauge will automatically adjust the rollers to compensate for any variations between the two rays if there is any variance between the two. It is also important to note that pipes are inspected for defects at the end of the process as well. A special machine can be used to perform a pipe test in one of the ways, which is by using a special method. To see if the pipe can hold the pressure, this machine fills the pipe with water and then increases the pressure to see if it works. There is a recycling program that returns defective pipes for scrap metal.
When it comes to the way these materials are specified, and what they mean to the exact characteristics of the pipe, there can be some confusion. According to the American Society for Testing and Materials (ASTM), along with the American Society of Mechanical Engineers (ASME) and the American Petroleum Institute (API), the American Society for Testing and Materials is the most reputable organization to reference for pipe specifications in North America.
Nominal Pipe Size
The size of a pipe is often referred to as the “Nominal Pipe Size” or NPS. The origin of the NPS numbers for smaller pipes (< NPS 12) can be distinguished from the origin of the NPS numbers for pipes with larger diameters. The external or outer diameter (OD) of all pipes of a specific NPS number, however, is the same in terms of size. Depending on the thickness of the metal wall, the internal diameter of the metal will vary. As a result of this, all of the piping that has a particular NPS number can be supported by the same structural supports regardless of the thickness of the wall of the pipe.
It is used to describe the wall thickness of steel pipes through the use of steel pipe schedules. In order to ensure that it affects the strength of the pipe directly, since it is a significant parameter, it has to be controlled properly. A pipe schedule is a dimensionless number and it is calculated using a design formula based on the wall thickness of a pipe, given the design pressure and allowable stress, as well as the design temperature. There is a direct correlation between the thickness of the wall of the pipe and the schedule number. Therefore, the schedule number of a pipe defines the internal diameter, since the OD of a pipe is defined by the number of the NPS.
As a result of the NPS, which defines the outer diameter of the pipe, and the schedule, which specifies the thickness of the wall, it is possible to calculate the weight of a pipe. For determining the constant, the formula uses the theoretical weight of steel, which is 40.8 pounds per square foot per inch of thickness, which is based on the theoretical weight of steel. The weight of a pipe can be represented by the following formula, where t represents thickness, OD represents outer diameter, and W represents weight: W = 10.69 x t (OD – t)
Standard manufacturing standards for pipes require a series of tests to be performed on their chemical composition as well as a series of tests to be performed on their mechanical strength. As a result of being forged from the same cast ingot, all the pipe in heat has the same chemical composition since it was cast from the same ingot. As a result of mechanical testing, a lot of pipes may be involved, all of which have undergone the same heat treatment process and are all from the same furnace. This type of material is called traceable if it is supplied with the accompanying test reports. Occasionally, third-party verification of these tests may be required in critical applications. In this case, an independent lab will produce a certified material test report, and the material will be called certified this way.
The following are some examples of pipe standards or piping classes that are widely used:
- (Seamless carbon steel pipes for high-temperature service according to ASME SA106 Grade B)
- It is a seamless and welded austenitic stainless steel pipe that conforms to ASTM A312.
- In accordance with ASTM C76 (Concrete Pipes)
- The ASTM A36 standard specifies the use of carbon steel pipes for structural or low-pressure applications
- There is an ASTM A795 standard for steel pipe that is specifically designed for fire sprinkler systems.