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Pipes play a vital role in several process-based businesses. From transportation services to extraction and acting as channels of distribution, different materials are used in their manufacture. Typically, they fit into two construction types - seamless and welded. Although the function they perform is the same, the method of construction differs.

Welded v/s seamless

Welded Pipes

A welded pipe would have a longitudinal seam on the length of its body, whereas a seamless one, as the name indicates - is constructed minus the seam. Therefore, the processes used to manufacture them vary. For instance, the assembly of welded pipes is via welding using procedures such as Electric resistance welded or ERW, Laser Welding or LW, Continuous Welding or CW, and lastly, Submerged Arc Welding or SAW. Welded constructions, though cheaper than a seamless product, tend to be weaker. Furthermore, the surface has a distinct seam line. Which through, extra processing can become lesser to some extent.

Pipes that belong to the seamless variety, on the other hand, are produced via a round billet using several processes. The surface of these components is smoother, homogeneous, and more even, unlike its welded counterpart. Also, they are much more robust and have superior corrosion resistance properties. The lack of seam eliminates the risk of intergranular corrosion, which is the case in welded products. Moreover, the seamless variety is less vulnerable to failure due to the absence of a seam. And the pressure handling capacity is approximately 20% more than that of a welded kind, making them excellent addition in high-pressure applications.

Manufacturing process of seamless pipes

Though the manufacturing method of this product is possible in a variety of schedules and sizes, there is a restriction. This restriction pertains to the production of large-sized products.
There are four methods that manufacturers use in their production - Mandrel Mill, Mannesmann Plug Mill, forging process as well as the Extrusion method.

Mandrel Mill

In this process, the steel billet in a rotary furnace will undergo heating at an elevated temperature. A rotary piercer in conjunction with a set of rollers - is what aids in the production of a mother or cylindrical hollow. The arrangement of the roller set ensures that the piercer remains at the center of the billet. The inner diameter or ID of the finished product is equivalent to the outer diameter or OD of the piercer. The thickness and outer diameter are an attribute of a secondary set of roller arrangement. Reheating the mandrel mill shell in a furnace completes the final rolling process. It is a manner wherein the final product also attains its distinct dimensions as well as certain micro-structural qualities. The exit process includes descaling by high-pressure water, which eliminates the iron oxide scale accumulated on its surface during reheating in the furnace. A clean and scale-free surface is critical for superior surface features. The reduction of a shell takes place in a stretch mill, keeping following the specification, after which they require trimming to the prescribed expansion.

Mannesmann Plug Mill

A German engineer named Mannesmann invented this method. Similar to the fore-mentioned process, the only difference is that in the Mandrel mill process, it is possible to achieve the inside diameter in a single pass. Whereas in the Mannesmann Plug Mill Process, a multi-stage reduction is a possibility.

Extrusion

This method includes the placement of a billet inside the die. The billet is heated. In this method, a hydraulic ram will push the billet against the piercing mandrel, which causes the material to flow from the cylindrical cavity connecting the die as well as the mandrel. This operation creates the pipe from the billet. Hence, the construction of this manufactured product is with a high thickness. This thickness is known as the mother hollow. In many instances, the production of secondary pipes makes use of this mother depression to fabricate pipes with diverse dimensions.

Forging

The forging method involves placing a hot billet inside a forging die. The diameter of the die is inappreciably larger than the finished pipe, and the creation of a cylindrical forging is when a hydraulic press of the hammer matches the inside diameter.

The completion of forging is followed by machining to accomplish the pipe's conclusive dimension. This manufacturing method is in use when the conventional techniques to produce large diameter pipes are not feasible.

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