In the industrial and civil infrastructure world, the fluid transport backbone and structural support is often a strong and solid piping. Some of the most common and basic ones include Large Diameter Mild Steel (MS) Pipes. These, as the name implies, consist of pipes manufactured of mild steel, a low-carbon steel that is strong, ductile, and welds readily, but has a large diameter that allows it to transfer large amounts of liquids, gases, and solids.
Usually, large diameter pipes are those whose outer diameter (OD) is 10 inches or larger. But in large infrastructural work it is common to find pipes between 24 inches to more than 120 inches. The main strength of them lies in their capability of carrying huge volumes with exceptional structural integrity that they cannot be ignored in a large number of heavy-duty uses.
The scale of these pipes dictates their use in critical, large-scale projects:
Water Transmission and Sewage Systems: They constitute the primary water mains of municipal water, raw water and large-diameter sewer mains.
Oil and Gas Pipelines: Large diameter ERW (Electric Resistance Welded) or DSAW (Double Submerged Arc Welded) pipes are very important in transporting crude oil, natural gas and other products of petrochemicals over long distances.
Civil Engineering and Piling: In construction, large diameter MS pipes are driven into the ground to serve as foundational piles, providing immense load-bearing capacity for bridges, high-rise buildings, and retaining walls.
Infrastructure Projects: Used in tunnels, culverts, and as casings for utility lines beneath roads and railways.
Industrial Use: Acting as ducts for high-volume air handling in power plants, dust collection systems, and as structural columns in large industrial sheds and warehouses.
The large diameter MS pipes have a significant impact in the manufacturing process that directly affects their strength, dimensional tolerances, and the applicability to a particular pressure and loads.
It is done by rolling out a flat piece of steel (skelp) into a cylinder shape and then welding longitudinal seam with high frequency electric current. The heat which is generated by the electrical resistance of the steel itself forms the weld. ERW pipes have a smooth, consistent weld seam and are known for their dimensional accuracy. They are generally more cost-effective for medium-pressure applications. Typical size range is usually up to 24 inches. Some of its common applications include water lines, plumbing, structural applications, and lower-pressure oil and gas services.
The SAW process is used in those cases when the diameter and pressure of the material exceed the range of ERW. It is the shaping of the plate of steel followed by welding the seam with the help of an arc that is struck with a layer of granular flux. This approach is further divided into two categories:
Longitudinal (LSAW): The weld is made in a single straight line along the length of the pipe. LSAW pipes are known for their superior strength in high-pressure applications.
Helical or Spiral (HSAW/SSAW): The pipe is made by helical winding of steel coils to make the steel coil a spiral seam. Such a technique permits the creation of far greater diameters out of a thin steel plate. This provides brilliant hoop strength; however, the spiral weld may be an issue with ultra-high-pressure services.
SAW pipes are thicker, heavier, and capable of withstanding much higher pressures and loads compared to ERW pipes. Its size ranges from 20 inches to over 100 inches. Common uses include long-distance high-pressure oil and gas transmission, piling, and major water transmission mains.
While less common in the very largest diameters due to manufacturing constraints, seamless pipes are created by piercing a solid steel billet to form a hollow shell without any seam. They are the strongest of all pipe types.
Their uniformity in strength and structure is due to the absence of a weld seam and they are ideal in extreme pressures, temperatures, and corrosive environments. Usually available to a maximum of 24 inches, although this point is expensive and difficult to produce, especially beyond that. Mostly, it is employed in high-pressure boiler tubes, oil and gas well casing, and critical process industry applications.
When selecting a large diameter MS pipe, several specifications are critical:
Material Properties: Specify the steel grade (e.g., ASTM A36, A53, A106, A500 or IS 1239, IS 3589) along with its yield strength, tensile strength, and chemical composition, as these determine the material’s strength, ductility, and weldability.
Dimension & Tolerance: Determine nominal pipe size (NPS), actual outside diameter and wall thickness, required length of the pipe and required pipe to be uniform in thickness and round.
Manufacturing Process: Pipes can be seamless or welded—ERW for low to medium pressure and SAW (LSAW or HSAW) for large diameter, high-pressure, or structural uses.
End Connections: Pipe ends can be plain for welding or couplings, bevelled for butt-welding, threaded for smaller sizes, or flanged for bolted connections to other equipment.
To sum up, large diameter MS pipes are the workhorses of modern infrastructure. Knowledge on the difference between the ERW, LSAW and the HSAW type, as well as the main specifications such as diameter, schedule and steel grade is vital to engineers, project managers and procurement specialists to be able to select the correct type of pipe to use in a given job as this helps in achieving safety, efficiency, and long life.
