There are two common types of stainless steel tubing used in manufacturing and fabrication. The first is seamless tubing. The second is welded tubing, which is one of the most versatile metal alloys available to manufacturers. A person’s decision on whether to use seamless or welded tubing is usually determined by the product’s application requirements. In choosing between the two keep in mind that first the tubing must be compliant with your project specifications, and secondly, it must meet the conditions for which it will ultimately be used.During the manufacturing process, seamless meaning steel pipes are manufactured by rolling the round steel billet through hot and cold rolling processes, as well as cold drawing, without a seam appearing on the body of the pipe.
Steel pipes are manufactured from flat steel plate, and the seams of the pipe are welded onto the body of the pipe. ERW pipes, LSAW pipes, and SSAW pipes all belong to this category.
In Octal, you can learn about the differences between seamless and welded pipes in terms of raw materials, manufacturing processes, performances, appearances, sizes, applications, and costs.
Historical perspectives and use cases for welded vs. seamless steel pipe
Generally, welded pipe was considered inherently weaker because it included a weld seam. Seam pipe, on the other hand, lacked this perceived structural flaw and was considered safer as a result. However, welded pipes are not considered weaker than steel pipe due to their seams, but manufacturing techniques have improved and quality assurance programs have been implemented so that as long as the tolerances of the pipe are not exceeded, welded pipe will perform as intended. As much as seamless piping may appear to have a distinct advantage, there is no doubt that it does have some limitations in its performance due to the rolling and stretching process, which produces inconsistencies in the wall thickness as opposed to steel sheets that are destined for welding.
There is still a lingering perception that these perceptions influenced the standards for ERW and seamless steel pipe manufacturing and specification. In the oil and gas, power generation, and pharmaceutical industries, seamless piping is required for many high-pressure, high-temperature applications. It is generally believed that plastic piping (which is generally more cost-effective and more widely available) should be specified across all industries, provided that the temperature, pressure, and other conditions are within the parameters noted in the applicable standards.
While ERW and seamless steel pipes are both able to be specified interchangeably, it makes no sense to specify seamless pipe when cheaper welded pipe is equally good for structural applications. So, it doesn’t make sense to specify seamless pipe when cheaper welded pipe is also equally good for structural applications.
How is Seamless steel pipe made?
Using a perforated tube as a raw material, API 5L and ASTM Seamless Steel Pipe can be produced by hot rolling, cold rolling, or cold drawing. Steel ingots or solid tubes are used as raw materials. It is possible to form hot rolled seamless steel pipes using billet forging, perforating, rolling, shaping, and other processes. Cold-drawn seamless pipes are formed through the process of cold-drawn forming. They can be made for large diameter pipes and thick walled seamless pipes. Small diameter and thin wall seamless pipes are usually made in this way because of their relatively low material strength as well as their smooth appearance and internal control surface. It is usually made from carbon steel, low alloy steel, alloy steel and stainless steel. The seamless steel pipes can be rolled with carbon steel, low alloy steel, alloy steel, and stainless steel. There are many industries in which seamless steel pipes can be used: Pipelines, thermal services, mechanical industries, chemical industry, etc.
Manufacturing seamless pipe
In order for seamless piping to be made, a solid cylindrical piece of steel called a billet is used. As soon as billets are still hot, they are pierced through the center with a mandrel, and then rolled and stretched to shape. In order for the billet to meet the specifications specified by the customer order, it is precisely rolled and stretched so it meets the dimensions, diameters, and wall thickness specified by the customer.
There are some seamless process types that harden during manufacturing and therefore do not require heat treatment after they are manufactured. But there are others that do require heat treatment after they are manufactured. For more information, consult the specification of the seamless pipe type you’re considering. Seamless definition means a solid round shape known as “billets” which are then heated and cast over a form such as a piercing rod to create a hollow tube or shell.
Stainless steel tubes are formed by rolling strips or sheets into tube shapes, then welding the seam longitudinally. Hot forming tubing is better than cold forming tubing in terms of smoothness and tolerances. Cold forming produces stronger tubes with a smoother finish. However, both methods produce steel tubes that are strong, durable, and corrosion-resistant. Cold rolling and forging can be used to further process the seam. Similarly to seamless tubing, welded tubes can also be drawn in a similar way to the seamless tube in order to produce a better surface finish and tighter tolerances as well as a finer weld seam.
How is Welded steel pipe made
Pipes made from API 5L or ASTM welded steel include pipe made from LSAW, pipe made from SSAW, and pipe made from ERW. There are several manufacturing processes involved in making welded steel pipes. The first step is to bend the steel plate, then a welding process is used to form circular, square, and other shapes. Welded steel pipes have high production efficiency, low costs and the ability to save materials. With excellent corrosion resistance in acidic environments, it has been widely applied in aviation, aerospace, energy, electronics, automobiles, light industries and other industries.
Manufacturing welded pipe
As the name suggests, the process of welding pipe begins with the skelp, which is a long, coiled ribbon of steel that is cut to the length that is desired. In the end, the width of that sheet’s short ends can be used to calculate the pipe’s eventual outside diameter as the length of the sheet’s shorter ends is used to determine the pipe’s exterior circumference.
ERW manufacturing is a method that involves feeding rectangular sheets into a rolling machine so that the longer sides are rolled up toward each other, creating a cylinder. A high-frequency electrical current is passed between the edges to melt and fuse them together in a continuous process.With ERW, there is no fusion metal used at the time of the welding process, and the weld tube hot cannot be seen or felt as it happens with double submerged arc welding (DSAW). This leaves behind an obvious weld bead that has to be removed depending on the application in order to obtain the correct end product.
There has been an improvement in welding techniques over the years. One of the most significant advances has been the switch to high-frequency electric currents for welding. Low-frequency ERW produced seams that were more likely to corrosion and fail than high-frequency ERW.Most welded pipe types require heat treatment after manufacture.
It is important to understand the distinction between welded and seamless tubing, as knowing that distinction will assist in determining which tubing is suitable for a particular application. There is no welded seam in seamless tubing, as defined by its name alone. Welded tubing is the tubing that is not welded together. In order to manufacture the tubing, it must be drawn from a solid billet of stainless steel, which is then extruded into a hollow shape and then sold to customers. As soon as the billets are heated, they are formed into an oblong circular mold that is hollowed out in an piercing mill in preparation for hollowing. Once the molds are hot, they are drawn through a mandrel rod and extended. As a result of the mandrel milling process, the molds have been increased by twenty times, giving them the appearance of seamless tubes. The tubing can also be shaped through pilgering, cold rolling, or cold drawing, depending on the shape of the application.
Choosing Between Welded and Seamless
In terms of choosing between welded and seamless tubing, there are both benefits and drawbacks to consider.
It is generally understood that seamless tubes are completely homogeneous tubes, allowing seamless tubes to be more strong, more corrosion resistant, and more able to withstand higher pressures than welded tubes because of their properties. It is a characteristic that makes them more suitable for critical applications in harsh environments, however, it also has a cost associated with it.
These benefits include:
- Superior corrosion resistance
- Higher pressure resistance
- Oil and gas control lines
- Chemical injection lines
- Below sea safety valves
- Steam and heat trace bundles that are used in chemical processing plants
- Fluid and gas transfer
Since welded tubing has a simpler manufacturing process than seamless tubing, it is generally less expensive than seamless tubing. In addition, it is readily available in long continuous lengths, as seamless tubing is. Both welded tubing sizes and seamless tubing sizes are both able to be manufactured in the same amount of time for a standard industrial tube and steel size. Seamless tubing has a higher cost than seamless tubing be offset in smaller manufacturing runs if less quantity is required. If you choose to go with seamless tubing that is not custom sized, you can have it produced and delivered more quickly, but the cost of this tubing is higher.
- Readily available in long lengths
- Fast lead times
- Architectural applications
- Hypodermic needles
- Automotive industry
- Food and beverage industry
- Marine industry
- Pharmaceutical industry
Costs of Welded vs Seamless
A seamless or welded tubing’s cost is also affected by the strength and durability it has. The ease with which welded tubing is manufactured makes it possible to produce tubing with larger diameters and thinner walls at less cost. Such properties can, however, be hard to achieve with seamless tubing. On the other hand, seamless tubing is more easily able to produce thick walls. For applications such as heavy wall tubing and applications which need to or can withstand high pressure or require performance in extreme environments, seamless tubing is often preferred over welded tubing.
Seamless vs welded steel pipe differences
1. Appearance difference
Steel pipe is produced using steel billets as their raw material. This billet, because of its inner surface defects, cannot be eliminated by hot rolling process, but can only be polished after the product has been finished. During wall reduction process, these defects can only be partially eliminated, which compromises the quality of the product.
The welded steel pipe is made from steel coils, which is one of the raw materials used to make these types of pipes. The surface quality of these coils are similar to that of the pipe, and it is easy to control.
Welded steel pipes have a much better surface quality than seamless steel pipes, so welding steel pipes are a better choice.
2. Molding process differences
As part of the rolling process, seamless steel pipes can be formed once during the process.
Generally speaking, welded steel pipes can either be manufactured from steel strip or steel plate, which is bent and then welded using different welding processes.
3. Performance and Usage
There is a considerable difference between seamless steel pipe and ERW welded steel pipe in terms of pressure capacity and strength. Therefore, seamless steel pipe is widely used in industries such as high pressure equipment, thermal heating, boiler.
There is generally a weak point in welding steel pipe, which is the welding seam. It is the quality of the welding seam that affects the performance of the pipe.
Due to the fact that welded steel pipes aren’t as reliable as seamless steel pipes, people are generally inclined to opt for seamless steel pipelines only because they can handle more pressure than welded steel pipes in terms of working pressure. As a matter of fact, Seamless steel pipes are used for industrial pipeline construction only because they are so reliable. Pipes are subjected to extreme heat, chemical, and mechanical loads. In aerospace, automobile, and electronics industries, where budgets are relatively low and work pressures are relatively low, welded pipes are more preferred.
4. Available Sizes differences
As far as most seamless steel pipe manufacturers in China are concerned, they usually produce original seamless pipe sizes with a maximum diameter of 20 inches, 508 millimeters. However, because of equipment limitations, the OD of seamless steel pipe is usually smaller than 16 inches, 406.4 millimeters. And if the client wishes to purchase seamless steel pipe in sizes larger than the above sizes, then hot expanding machining should be used. However, in general, these kinds of hot expanded seamless steel pipes are not of the same quality as the original seamless steel pipes.
In contrast, welded steel pipes don’t have these limitations, with sizes available from 1-1/2 inch 48.3mm to 100 inch 2540mm with a range of diameters from 1.25 to 1.75 inches.
5. Cost and prices
There are several reasons why seamless steel pipes are usually more expensive than welded steel pipes, including the raw material, the manufacturing process, and the equipment used to manufacture them. You should not hesitate to purchase seamless steel pipes for the same dimensions if you are faced with this situation when the price of welded pipe can be high due to market pressure.