Seamless Pipe Manufacturing Process

Mandrel Mill Process

The Mandrel Mill process begins with a solid round billet, which is heated in a rotating hearth furnace and then pierced using a piercer. The perforated billet or hollow shell is then rolled by a mandrel mill to reduce the outer diameter and wall thickness, resulting in the formation of a multiple-length mother tube.

• This method creates smaller diameters of seamless pipe, generally ranging from 1 to 6 inches (25 to 150 mm) in diameter.
• The steel ingot is perforated and heated to 2,370 °F (1,300 °C).
• A mandrel is inserted into the tube, and the assembly is rolled (mandrel) and milled.
• The mandrel mill, as opposed to the plug mill, continually decreases wall thickness with a sequence of pairs of curved rollers positioned at 90° angles.
• The pipe is reheated before being run through a multi-strand stretch-reducing mill to decrease the diameter to the final diameter.
• The pipe is cut to length before being heat-treated, straightened, inspected, and hydrostatically tested.

Mannesmann Plug Mill Pipe Manufacturing Process

In the plug mill process, a solid round billet is heated uniformly in a rotating hearth furnace before being pierced. The round billet is pierced using a cross-roll piercer, where the billet is pressed against a plug and rolled between the rollers and the plug. The resulting perforated billet or hollow tube is then rolled and reduced, either hot or cold.

• This method creates bigger diameters of seamless pipe, generally ranging from 6 to 16 inches (150 to 400 mm) in diameter.
• A steel ingot weighing up to two tonnes is heated to 2,370 degrees Fahrenheit (1,300 degrees Celsius) and perforated.
• A rotating elongator is used to widen the opening in the hollow shell, resulting in a short, thick-walled tube known as a bloom.
• The bloom is then pushed through with an internal stopper around the same diameter as the completed pipe diameter.
• The bloom holding the plug is subsequently run through the plug mill's rollers.
• Roll rotation decreases the wall thickness.
• To guarantee roundness, the tube is turned through 90° for each trip through the plug mill. 
• After that, the tube is sent through a reeling mill and a reduction mill to smooth the wall thickness and obtain the finishing dimensions.
• The tube is cut to length before being heat-treated, straightened, inspected, and hydrostatically tested.

Pilgering & Cold Drawing Process for Producing Smaller Size Seamless Tubes from Larger Size Pipes

The pilgering process is a commonly used method for producing small-sized Seamless Pipes and Tubes , particularly when the pipe thickness needs to be reduced. It is also used for producing Stainless Steel Seamless Pipes in sizes ranging from 14" to 2". It improves the surface finish and quality of the pipe or tube.

In general, the pilgering procedure serves two purposes:

• Most significantly, pilgering is a cold working method that dramatically enhances the grain structure of the material.
• It is a method of rapidly lowering an existing tube's exterior and internal diameter. On some alloys, reduction rates can reach approximately 90 per cent. Ring dies, and a tapered mandrel is used in the cold mill pilgering process to decrease tube cross sections by up to 90%.

The cold drawing technique does comparable work to the Pilger process; however, the size reduction rates are normally limited to 15 to 35 per cent depending on the alloy.