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`PIPING ENGINNERING
`
`Introduction to Seamless Pipe Manufacturing
`
`Steel pipes are long, hollow tubes that are used mainly to convey products from one location to another. They
`are produced mainly by two distinct manufacturing methods which result in either a welded pipe or seamless
`pipe. In both the manufacturing methods, raw steel is first cast into a more workable starting form (hot billet
`or flat strip). It is then made into a pipe by stretching the hot steel billet out into a seamless pipe or forcing
`the edges of flat steel strip together and sealing them with a weld. In this article we will discuss the various
`methods involved in seamless pipe manufacturing.
`
`Mandrel Mill Process
`
`In the Mandrel Mill Process, a solid round steel billet is used. The billet is charged into a rotary hearth
`furnace. After the billet is discharged from the rotary hearth furnace, a small hole is punched into its end. This
`indentation acts as a starting point to aid in rotary piercing.
`
`Rotary piercing is a very fast and dynamic rolling process that cross rolls the preheated billet between two
`barrel-shaped rolls at a high speed. The cross rolling causes high tensile stresses at the center of the
`billet. The design of the piercer rolls causes the metal to flow along the roll and over a piercer point as it exits
`the process. The piercer point is a high-temperature, water-cooled alloy tool designed to allow the metal to
`flow over it as a pipe shell forms from the rotary process. Once the pierced pipe shell is produced, it is
`immediately transferred to the floating mandrel mill.
`
`The floating mandrel mill comprises eight rolling stands using 16 rolls and a set of mandrel bars. These
`mandrel bars are inserted into the pierced pipe shell and then conveyed into the mandrel mill and rolled into
`an intermediate size pipe shell. The mechanism of rolling the pipe shell through the mandrel mill with the
`mandrel bar inside acts as a control to create an intermediate standard outside diameter (OD) and a
`controlled wall thickness, based on the resultant dimension of the mandrel bar set.
`
`The mandrel mill shell is then reheated in a reheat furnace so that it can complete the final rolling process
`and gain its final dimensions and micro-structural qualities. Upon exit from the reheat furnace, the tube
`receives a high-pressure water descale, removing the iron oxide scale that formed in the reheat furnace. A
`clean, scale-free surface is critical for good surface quality.
`
`The pipe shell is further reduced to specified dimensions by the stretch mill. The pipes then are conveyed to
`the cutoff mechanism, where they are cut to the prescribed length. then these pipes are bundled and directed
`to subsequent finishing and inspection operations before shipment.
`
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`Page 1 of 3 (PGR2021-00078)
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`Mandrel Mill Process
`
`Mannesmann Plug Mill Process
`
`1\lannesmann Plug Mill Process is somewhat similar to Mandrel Mill Process with major difference in rolling
`plug mill in place of mandrel mill.
`
`In the rolling plug mill, a pair of conical shaped rolls - one arranged above the other - operates in the
`opposite direction to the material flow. The thick-walled hollow pipe shell, with a cylindrical mandrel inside
`it, is guided towards the plug mill rolls. A,; soon as it is gripped by the tapered portion of the work pass, a
`small material wave is sheared off the hollow pipe shell. This wave is forged to the desired wall thickness on
`the mandrel by the smoothing portion of the work pass, with the hollow pipe shell plus mandrel moving
`backwards in the same direction as the rolls are rotating - i.e. in the opposite direction to the rolling - until
`they reach the idler pass of the rolls and are released. As the hollow pipe shell is rotated it is once again
`pushed forward between the rolls, and a new rolling cycle begins.
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`Mannesmann Plug Mill Process
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`
`Extrusion Process
`
`Extrusion is a metal forming process in which a work piece usually a round billet is forced to flow through a
`die of a smaller cross sectional area, thus forming the work to the new cross section. The length of the
`extruded part will vary, dependent upon the amount of material in the work piece and the profile extruded.
`Numerous cross sections are manufactured by this method.
`
`Pipes can be directly extruded with the use of a mandrel attached to the dummy block. A hole is created
`through the work, parallel to the axis over which the ram applies the force to form the extrusion. The mandrel
`is fitted within this hole. Once the operation begins, the ram is forced forward. The extruded metal flows
`between the mandrel and the die surfaces, forming the part. The interior profile of the metal extrusion is
`formed by the mandrel, while the exterior profile is formed by the extruding die.
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`Page 2 of 3 (PGR2021-00078)
`G&H DIVERSIFIED MANUFACTURING, LP v. DYNAENERGETICS EUROPE GMBH
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`Extrusion Process
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`Cc.xi~, Standards and Rn.:oIIllllrndni Practices
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