How Are Pipes Made? The Fabrication Process

Seamless or welded steel pipes

Steel pipes play a critical role in the oil and gas industry, serving as vessels for storing and transporting hydrocarbons in various sizes. These pipes come in two main types: seamless, crafted by heating and piercing a steel billet, and welded, formed by curving long flat steel pieces into a tube shape and sealing them along the seam. Both kinds undergo a three-step process: initial transformation of raw steel into a more manageable form, fabrication on a production line within a pipe mill, and finally, customization according to customer specifications.

Blooms and slabs

The journey begins with the melting of iron ore and coke, forming raw steel ingots that are then processed into "blooms" and "slabs." Blooms eventually transform into the billets used for creating seamless pipes, while slabs are destined to become welded pipes.

ERW MS Pipe Making Machine

Welded pipe

For welded pipes, the steel slabs undergo further treatment involving heating, coating, descaling, and rolling, resulting in the formation of narrow strips called skelp. These skelp strips are coiled and forwarded for the production of welded pipes.

Electric Resistance Welding (ERW):

In the ERW process, the steel skelp is unwound, heated, and guided through grooved rollers, causing its ends to curl up and take on the shape of a pipe. The unwelded pipe then moves through welding electrodes, where the metal's resistance to the current generates heat and molten pools at the edges, resulting in the formation of the weld.

High-Frequency Induction Welding (HFI):

Similar to ERW, HFI welding utilizes an induction coil to generate the current. HFI-welded pipes are preferred in the oil and gas industry due to the process yielding a stronger and higher-quality weld, particularly suitable for pipes operating under high fatigue and stress conditions.

Longitudinal Submerged Arc Welding (LSAW):

In LSAW, the weld and the arc zone are submerged beneath a layer of fusible flux. Unlike pipes made from coils, LSAW pipes are formed from steel plates and are utilized for larger diameters exceeding 24 inches or pipes requiring notably high wall thickness.

Seamless pipe

Seamless pipe is made when square steel billets are heated and moulded into cylinder shapes called “rounds”. The round is heated to white-hot in a furnace and rolled under high pressure. As the billet stretches out a hole forms in the centre and a bullet-shaped piercer point is pushed through. Pipes with larger diameters undergo the mandrel mill process, wherein the pierced pipe shell is rolled through a mandrel mill containing internal mandrel bars. This method ensures a more uniform outside diameter (OD) and regulates the wall thickness (WT) of the pipe. On the other hand, smaller diameter pipes are manufactured using the plug mill process.

Oil and gas industry usage

Various types of pipes are extensively utilized across the oil and gas industry. Seamless pipes, favored for their absence of seams leading to fewer stress points and enhanced mechanical strength, can be shaped into more precise and predictable forms. However, their production is notably pricier compared to welded pipes and involves extended lead times due to limited manufacturing facilities. Despite welded pipes having seams that might imply potential weak points, ongoing advancements in welding technology have substantially enhanced their quality. Welded pipes offer more uniform wall thickness and shorter lead times in production compared to seamless pipes.