Seamless stainless steel specialty tubing is used in many uses, including air, steam and liquid flow in harsh conditions. Many professional factories in this region manufacture smooth, stainless steel tubes which range from 1 inch in diameter to finer than a human hair, sometimes in continuous lengths which may exceed 1 mile.
Extruding, pistol grinding, or cutting are common techniques for producing smooth stainless steel tubing. Nevertheless, the extrusion cycle produces the most standardized OD (outside diameter) and, in the center, the most intense ID (inside diameter). Extrusion is also the only form best suitable for long-lasting smooth, stainless steel coil tubing. The raw material starts off in the shape of smooth hot extruded tubing. The substance is then depleted in ice. At this stage, the raw material is processed in a long straight shape by means of tube reducers known as pilger mills.
Cold pilgering can maintain uniform ODs and concentrated IDs as it is a longitudinal cold-rolling process that reduces the diameter of the steel tube and the thickness of the wall in one operation. This approach achieves sectional reductions of over 90 per cent for various material forms in a single operational period.
Lubricants are used in reduction of the tubing on the OD and ID, and is then degreased in preparation for annealing. Usually this method generates lengths after reduction from around 40 feet to 160 feet in total. Cold reduction is the most effective process for the development of long stretches of smooth tubing in a coil shape.
On specially designed equipment straight lengths of the tube are drawn cold in coil form. Because cold drawing decreases OD, ID and wall thicknesses, the tube rises in length as the line is drawn.
Main Drawing Types
There are two main drawing operations used.
- Floating Plug
Floating plug drawing is the method of pushing the tube into a conical die, then placing a floating plug into the ID. The resultant ID and thickness of the wall is a scale dependent on the die and pin. Floating plug drawing provides a cleaner result that is more robust but can only be seen on fairly light wall products.
- Sink Drawing
Sink drawing is the mechanism that draws the tubing into a conical die and decides the corresponding ID and wall thickness depending on the drawing and tube parameters. Sink drawing is used in high-pressure applications where strong relative wall thickness is needed. Usually the ID is a little rougher than the floating plug drawing.
As described above, the tube coils have OD and ID lubricants to help in drawing processes. The lubricant is withdrawn (degraded) from the pipe for most end-use applications (liquid delivery, surgical, etc.). It is done in one stage in a wide degreasing vessel with solvent.
Upon cold reduction, long straight lengths and coils are annealed to eliminate internal pressures and to preserve the material’s crystalline structure to enable for more cold activity. The accelerated cooling process turns the dry, brittle and hard substance back into flexible and ductile content.
Such steps are replicated before they meet the required measurements.
Those tubing will be constructed according to relevant ASTM specifications and thoroughly inspected for potential faults before being approved for shipping to the consumer.
This is hydrostatically tested after the tube is completely shaped to the required standard to maintain credibility. Hydrostatic inspection defines the standard and verifies whether the tubing follows. This verification process can be used to obtain several types of information. Data can be identified through the hydrotest process, such as:
- Material malfunctions
- Mechanical Attributes
- Clear hard spots which will collapse while there is hydrogen
Stainless steel coil tubing can be level wound on spools for shipment or straightened and cut to specific lengths designated by the customer. Products can be polished and stenciled with pertinent information for lot traceability and manufacturing identification.