The manufacture of steel pipe dates from the early 1800’s. Initially, pipe was manufactured by hand – by heating, bending, lapping, and hammering the edges together. The first automated pipe manufacturing process was introduced in 1812 in England. Manufacturing processes have continually improved since that time. Some popular pipe manufacturing techniques are described below.
If you are looking for more details, kindly visit erw pipe manufacturing process.
The use of lap welding to manufacture pipe was introduced in the early 1920’s. Although the method is no longer employed, some pipe that was manufactured using the lap welding process is still in use today.
In the lap welding process, steel was heated in a furnace and then rolled into the shape of a cylinder. The edges of the steel plate were then “scarfed”. Scarfing involves overlaying the inner edge of the steel plate, and the tapered edge of the opposite side of the plate. The seam was then welded using a welding ball, and the heated pipe was passed between rollers which forced the seam together to create a bond.
The welds produced by lap welding are not as reliable as those created using more modern methods. The American Society of Mechanical Engineers (ASME) has developed an equation for calculating the allowable operating pressure of pipe, based on the type of manufacturing process. This equation includes a variable known as a “joint factor”, which is based on the type of weld used to create the seam of the pipe. Seamless pipes have a joint factor of 1.0. Lap welded pipe has a joint factor of .6.
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. Initially this manufacturing process used low frequency A.C. current to heat the edges. This low frequency process was used from the 1920’s until 1970. In 1970, the low frequency process was superseded by a high frequency ERW process which produced a higher quality weld.
Over time, the welds of low frequency ERW pipe was found to be susceptible to selective seam corrosion, hook cracks, and inadequate bonding of the seams, so low frequency ERW is no longer used to manufacture pipe. The high frequency process is still being used to manufacture pipe for use in new pipeline construction.
Electric flash welded pipe was manufactured beginning in 1927. Flash welding was accomplished by forming a steel sheet into a cylindrical shape. The edges were heated until semi-molten, then forced together until molten steel was forced out of the joint and formed a bead. Like low frequency ERW pipe, the seams of flash welded pipe are susceptible to corrosion and hook cracks, but to a lesser extent than ERW pipe. This type of pipe is also susceptible to failures due to hard spots in the plate steel. Because the majority of flash welded pipe was produced by a single manufacturer, it is believed these hard spots occurred due to accidental quenching of the steel during the manufacturing process used by that particular manufacturer. Flash welding is no longer used to manufacture pipe.
Similar to other pipe manufacturing processes, the manufacture of Double Submerged Arc Welded Pipe involves first forming steel plates into cylindrical shapes. The edges of the rolled plate are formed so that V-shaped grooves are formed on the interior and exterior surfaces at the location of the seam. The pipe seam is then welded by a single pass of an arc welder on the interior and exterior surfaces (hence double submerged). The welding arc is submerged under flux.
The advantage of this process is that welds penetrate 100% of the pipe wall and produce a very strong bond of the pipe material.
Seamless pipe has been manufactured since the 1800’s. While the process has evolved, certain elements have remained the same. Seamless pipe is manufactured by piercing a hot round steel billet with a mandrel. The hollowed steel is than rolled and stretched to achieve the desired length and diameter. The main advantage of seamless pipe is the elimination of seam-related defects; however, the cost of manufacture is greater.
Early seamless pipe was susceptible to defects caused by impurities in the steel. As steel-making techniques improved, these defects were reduced, but they have not been totally eliminated. While it seems that seamless pipe would be preferable to formed, seam-welded pipe, the ability to improve characteristics desirable in pipe is limited. For this reason, seamless pipe is currently available in lower grades and wall thicknesses than welded pipe.
Conclusion
Continual advances in materials and welding techniques have resulted in dramatic improvements in the reliability of pipes. As mentioned, however, there is still pipe in use that is susceptible to corrosion and seam-related defects. These defects are identified through integrity assessments and are repaired when found.
Pipe manufactured today is subject to non-destructive tests such as ultrasonic testing and x-ray, as well as pressure-testing. Each individual section of pipe must be pressure-tested by the manufacturer, and new pipelines are also pressure-tested during the actual construction process.
Date of Revision: 12012011
Pipes are some of the most widely-used construction materials. They need to be durable in order to withstand different environmental changes that may cause a drastic change in pressure or temperature. As such, many manufacturing techniques exist in order to achieve industrial-grade pipes. The process of creating ERW steel pipes is one of these techniques. Doubling down on the many properties of steel, ERW pipes offer high strength and durability for fluid transmission and other structural applications.
What is ERW?
ERW stands for electric resistance welding and it is primarily used to describe a specific method in pipe manufacturing. In this process, two uncoiled rolls of steel sheets are joined together without the need for a welding filler wire or metal. Instead, the sheets are combined through the passage of an electrical current and a constant applied force. Unlike what you may notice across other methods of pipe fabrication, ERW pipe-making does not start out with a billet that is rolled before being further refined by a piercer point. Continue reading to learn more.
Contact us to discuss your requirements of ss pipe welding machine. Our experienced sales team can help you identify the options that best suit your needs.
Cold-forming is a method of working or forging a metal specimen — in this case, steel — usually in a room temperature environment. This means that the forging takes place below the steel’s recrystallization temperature, helping to remove the impurities from the material. When this occurs, the grain structuring of steel is transformed to become finer and less-coarse, therefore resulting in a hardened material with very little waste found in the machining process.
This is one of the main stages in the creation of ERW pipes. A sheet of steel is cold-rolled or formed into a cylindrical shape. With the absence of further heat-processing techniques, cold-forming is much faster and is suitable for high-speed production. The permanent hardening of the cold-forming process already results in a much stronger steel specimen before the welding stage takes place.
ERW pipe forming is an ongoing process that takes place in a constantly-moving machine. Though this is the case, the many stages that comprise it can still be identified and defined. After the cold-forming process, there is a passage of electrical current between the resulting edges of the cylindrical steel. They are gradually joined together through the current with the help of an induction coil, and a smooth pressure roll to maintain the cylindrical shaping.
The use of an induction coil creates a non-contact method of heating the material. It is typically installed around the steel specimen which is subject to the induction. To control the amount of electrical current that’s distributed throughout the material, an impeder is also added to the ERW machining process. This means that the energy is refocused towards welding the joints of the steel.
Forming is another process that takes place in ERW manufacturing. The steel coils that pass through the ERW-making machine, as mentioned before, result in cylindrical-shaped sheets that need to be welded by way of electrical current. To better illustrate this, the sheets first appear to be U-shape in appearance, that have several open welded joints, or edges, as they’re called.
All throughout the process, the machine ensures that the resulting U-shaped steel retains this formation in order to avoid defects and irregularities in the fabrication of the ERW pipe. The steel sheet first passes through rolling components before being subject to gage forming, resulting in a uniformed U-shaped cross-section.
If you’ve ever encountered seamless and non-seamless pipes before, then it’s easy to spot where the manufacturing techniques begin to differ, once they’re compared with ERW pipes. Seamless pipes may appear to be similar in appearance with ERW pipes, but the latter makes use of a non-contact electrical current. No welding takes place in seamless pipes — hence resulting in a continuously-smooth surface that has no visible edges or joints. Seamed pipes, on the other hand, may either make use of a welding filler — something that is not found in the ERW welding process.
Pipe manufacturers always ensure that the welded pipes they’ve made can be suitable for a wide range of uses, such as HVAC systems or petrochemical plants. Despite stringent quality control, it is possible for instances of uneven welding pressure to occur in seamed pipes. Some problems that may take place include pipe leakage or damage that is ultimately far less common across ERW pipes because of their uniform pressure and strength distribution.
After welding the U-shaped joints together, an ERW pipe can now be subject to post-processing techniques to further enhance the properties of the material, as well as its usability.
It’s sized and cut according to specific dimensions, depending on the type of application. With this in mind, ERW pipes can be cut in a wide variety of pipe sizing and lengths that may exhibit differences in the thickness, diameter, or length. To accommodate different fittings, it may also be possible for the pipe ends to be further shaped with an end-facing machine.
The process of creating ERW steel pipes are distinct, in that it makes use of an electrical current to weld the joints in place. In this technique, instead of having to use a welding filler to join the edges together, a non-contact induction coil is used with the help of an impeder to concentrate the current to the edges of the pipe.
ERW pipes are far more durable and stronger compared to welded pipes, largely due to the smoother finish. This creates an even distribution of pressure and temperature, especially for HVAC applications, or may also lead to a more consistent transmission of fluids, preventing instances of bursting or leakages.
Share this Blog
Are you interested in learning more about ss tube mill machine? Contact us today to secure an expert consultation!