Seamless Pipe Manufacturing Process - Shrikant Steel Centre

Mandrel Mill Process

A solid round (billet) is utilised in the Mandrel Mill Process. It is heated in a rotating hearth furnace before pierced with a piercer. A mandrel mill rolls the perforated billet or hollow shell to lower the outer diameter and wall thickness, forming a multiple-length mother tube. The stretch reducer reheats the mother tube and reduces it to the prescribed size. Before shipment, the tube is cooled, cut, straightened, and subjected to finishing and inspection operations.

• 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

A solid round billet is used in the plug mill operation. The spherical billet is first evenly heated in the rotating hearth heating furnace before perforating. A cross-roll piercer is used to pierce the round billets. To pierce the billet, the piercing mill forces it against a plug and then rolls it between the rollers and the plug. Afterwards, the perforated billet or hollow tube is rolled and reduced (hot or cold) to the specified outer diameter and wall thickness.

• 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

Pilger is one of the most frequently used techniques for producing seamless pipes in sizes ranging from 14" to 2", particularly when the pipe thickness needs to be decreased. Another method for producing small-sized seamless pipes and tubes. In general, the pilgering procedure serves two purposes:

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.