There exists two large categories of pipe construction: seamless steel pipe and welded steel pipe. There also exists an ongoing debate as to which construction method yields a better product. I will tell you now that it really depends on your application. Nonetheless, let’s take a closer look.
Seamless Steel Pipe
As the name implies, seamless steel does not have a weld seam. That is why it is seamless. It does not show the joint where two pipes are connected. To make a seamless pipe, the mill starts with a solid cylinder of steel called a billet. The billet is super-heated in the mill furnace, just to the point where it is about to lose shape. From the furnace, the billet is transferred and pierced. So, when the billet is red hot, the center of the billet is pushed out, creating a hollow cylinder. The hollow cylinder is then massaged over a series of rollers and dies to achieve the desired size. The result is a continuous steel cylinder of uniform strength. Unlike almost any other material in the world, seamless pipe is not manufactured to a specific length. Rather, a mill will make either “single random lengths” (SRLs) or “double random lengths (DRLs). An SRL ranges from about 18ft to 24ft and a DRL ranges from 35ft to 44ft. This range of lengths is a by-product of the manufacturing process. Specifying the minimum required length needed for a project or application becomes very important. Simply put, the process damages the ends of the pipe and as a finishing step the mill cuts off the damage. The damage is not uniform, so neither is the resulting pipe length. A great deal of variety exists between the different pipes. The drawback of seamless steel pipe is its concentricity. The wall thickness of seamless pipe will vary as you go down the pipe, sometimes starting larger and becoming smaller. This is due to the floating die used in the manufacturing process.
Seamless steel pipe is found in some of the more serious and important areas of our lives. Plumbers and HVAC companies use seamless pipe for houses, while businesses that deal with oil and gas use the pipe to transport their materials. Electric companies use the steel for rigid, durable structures and for the towers that support electrical lines. Rail companies and the shipping industry all use seamless steel pipe too because of the tremendous stress. That same reason is why wells dug for water also use seamless pipe. The depth of the holes and necessary reliability make seamless an obvious choice.
Is Seamless Steel Pipe Better Than Welded?
It really depends on your application or project, because different specs and grades of steel pipe have unique characteristics. One or the other may or may not be suitable for what you are doing. Weld pipe is used to move things like water in a yard sprinkling system or steam and gas. You would also find welded pipe is used for yard fences and more critical applications like structures. It is always recommended that you consult an engineer when designing a piping system. Seamless steel pipes might naturally be more durable and reliable because there is no seam, but that level of strength might not be needed for the project. One of the finer points of engineering is using the correct amount of materials without wasting more money than is necessary. Seamless steel pipes might then be necessary for machinery, as the stronger steel lasts longer and is less susceptible to failure. This comes at a cost though, as there might be a price difference. Welded pipes are often the cheaper of the two options. Keep in mind, though, that some evidence shows welded pipe might be stronger than seamless pipe, so carefully evaluating priorities and consulting with an engineer is a must.
There is also the aesthetic perspective to consider with seamless steel pipe. If the pipes will be exposed or featured in some way, the clean, finished look of seamless might be the best option. Welded pipes would obviously be perfectly acceptable if they are to remain permanently hidden in the walls of a building or underground. These parameters are obviously going to affect price, but one other factor does as well: supply.
The availability of seamless steel pipes is an important factor to consider. As with all things that relate to supply and demand, one variation might be more available than another and the price would adjust accordingly. Something that can really aid in the price and timeline of a project is checking ahead of time to see if either type of steel could work. Being dead set on one type over another would lead to problems if the preferred type is unavailable. Knowing in advance if both work would enable the buyer to take advantage of a low cost or abundance of one type. Again, checking to see if one is more necessary than another is absolutely important, but there are some circumstances that allow for either variation.
There are two major pipe construction categories available to people seeking pipes: seamless and welded. Surrounding the products these two construction methods create, there is a large ongoing debate as to which is better. The simple answer is that it varies depending on the individual construction project. Still, it is important to understand the details of each pipe.
Welded pipe has a weld seam running the longitudinal length of the pipe. Typically, welded pipe is manufactured from steel plate. A flat sheet of plate will be formed into a cylinder using force. Once the cylinder is formed the longitudinal seam is welded. Manufacturing welded pipe is less costly than seamless steel pipe. Often, welded pipe is sold in “dead lengths”. Unlike seamless that is sold in a range of lengths. Welded pipe has long been considered as inferior to seamless pipe due to its seam. Engineers consider the weld seam a weak point in the construction of the pipe. They are fearful that under stressful conditions the weld seam will burst. In recent years, this argument has been considered bogus. Scientific studies have shown that the weld seam is as strong, or stronger than the base material.
Is Welded Pipe better than Seamless?
Contacting an engineer about your specific project is your best option for answering this question because the answer depends on the pipes application. You also have to consider that fact that different specs and grades of steel pipe such as API 5L have unique characteristics. Take these differences into consideration when choosing which type of pipe to use.