Production and Processing Technology of Stainless Steel Seamless Pipe

1) Stainless steel seamless pipe (ss pipe) production process:

Simplify the main production process: Round steel → re-inspection → peeling → blanking → centering → heating → perforation → pickling → flat head → inspection and grinding → cold rolling (cold drawing) → degreasing → heat treatment → straightening → pipe cutting (set ruler) → pickling/passivation → finished product inspection (eddy current, ultrasonic, water pressure) → packaging and storage.

1. Round bar cutting: 

After receiving the round bar from the raw material warehouse, calculate the cutting length of the round bar according to the requirements of the process, and draw a line on the round bar. After the bow sawing machine is started, the grinding wheel is cut along the segment line, and the cut circle The steel is stacked separately according to the steel type, furnace number, production batch number and specification, and the ends are distinguished by different colors of paint.

2. Centering: 

When centering the cross-arm drilling machine, first find the center point on a section of the round steel, drill a sample hole, and then vertically fix it on the drilling machine table for centering. The centered round steel is stacked separately according to the steel type, furnace number, specification and production batch number.

3. Peeling: 

Peeling is carried out after the incoming material has passed the inspection. Peeling includes lathe peeling and whirlwind cutting. Lathe lathe peeling is performed on the lathe with a processing method of one clip and one top. Whirlwind cutting is to hang the round steel on the machine tool Perform whirl cutting.

4. Surface inspection: 

The quality inspection of the light round steel after peeling is carried out, and the existing surface defects are marked, and the grinding personnel will grind until it is qualified. The round steel that has passed the inspection is stacked separately according to steel type, furnace number, specification and production batch number.

5. Round steel heating: 

The round steel heating equipment includes a gas-type inclined bottom furnace and a gas-type box-type furnace. The gas-fired inclined-bottom furnace is used for heating when a large batch of incoming materials is supplied, and the gas-fired box-type furnace is used for heating when a small batch of incoming materials is supplied. When entering the furnace, the round steel with different steel types, furnace numbers and specifications is separated by the old outer film. When the round steel is heated, the steel turner uses tools to turn the steel to ensure that the round steel is heated evenly.

6. Hot-rolled piercing: 

Use piercing unit and air compressor. According to the specifications of the perforated round steel, select the corresponding guide plate and molybdenum plug, use the piercer to perforate the heated round steel, and the pierced waste pipe is randomly put into the water pool for full cooling.

7. Inspection and grinding: 

Inspect the inner and outer surfaces of the waste pipe to be smooth and flat, and there must be no skins, cracks, interlayers, deep pits, serious thread marks, tower iron, fried sticks, Baotou and sickle heads. The surface defects of waste tubes can be eliminated by local grinding. The waste pipes that have passed the inspection or the waste pipes that have passed the inspection after minor defects have been repaired are bound by the binding workers in the workshop according to the requirements, and stacked separately according to the steel type, furnace number, specification, and production batch number of the waste pipes.

8. Straightening: 

The raw material pipes from the piercing workshop are packed in bundles. The shape of the incoming raw pipe is bent and needs to be straightened. The equipment used for straightening is vertical straightening machine, horizontal straightening machine and vertical hydraulic press (used for pre-straightening when the bending degree of the steel pipe is large). In order to prevent the steel pipe from bouncing during straightening, a nylon sleeve is used to limit the steel pipe.

9. Pipe cutting: 

According to the production plan, the straightened raw pipe needs to be cut head and tail, and the equipment used is a grinding wheel cutting machine.

10. Pickling: 

The straightened steel pipe needs to be pickled to remove the scale and impurities on the surface of the waste pipe. Pickling of steel pipes is carried out in the pickling workshop, and the steel pipes are slowly hoisted into the pickling tank for pickling by a crane.

11. Grinding, endoscopic inspection and internal polishing: 

pickling qualified steel pipes enter the external surface grinding process, and the steel pipes after grinding are subjected to endoscopic inspection, and internal polishing is required for unqualified products or processes with special requirements deal with.

12. Cold rolling process/cold drawing process

Cold rolling: the steel pipe is rolled by the rolls of the cold rolling mill, and the size and length of the steel pipe are changed by continuous cold deformation. The cold rolled steel pipe has a fast forming speed, a large amount of deformation, and a high output.

Cold drawing: use a cold drawing machine to expand and reduce the wall of the steel pipe without heating to change the size and length of the steel pipe. The cold drawn steel pipe has high dimensional accuracy and good surface finish. The disadvantage is that the residual stress is large, and Large-diameter cold-drawn pipes have more times, and the finished product forming speed is slow. The specific process of cold drawing includes:

① Heading and welding head: Before cold drawing, one end of the steel pipe needs to be headed (small-diameter steel pipe) or welded (large-diameter steel pipe) to prepare for the drawing process. A small amount of special specification steel pipe needs to be heated before it is headed.
② Lubrication and baking: Before cold drawing of the steel pipe after head (welding head), the inner hole and outer surface of the steel pipe need to be lubricated, and the steel pipe coated with lubricant must be dried before cold drawing.
③ Cold drawing: The steel pipe after the lubricant is dried enters the cold drawing process, and the equipment used for cold drawing is a chain cold drawing machine and a hydraulic cold drawing machine.

13. Degreasing: 

The purpose of degreasing is to remove the rolling mill oil attached to the inner wall and outer surface of the steel pipe after rolling by rinsing, so as to avoid polluting the steel surface during annealing and preventing carburization.

14. Heat treatment: 

Heat treatment restores the shape of the material through recrystallization and reduces the deformation resistance of the metal. The heat treatment equipment is natural gas solid solution heat treatment furnace.

15. Finished product pickling: 

After cutting the steel pipe, the finished product pickling is carried out, the purpose of which is to passivate the surface, so that a layer of oxidation protection film is formed on the surface of the steel pipe, and the corrosion resistance of the steel pipe is enhanced.

16. Finished product inspection: 

The process of finished product inspection and test is mainly surface inspection → eddy inspection → super inspection → water pressure → air pressure inspection. Surface inspection is mainly to manually check whether there is any defect on the surface of the steel pipe, whether the length of the steel pipe and the size of the outer wall are qualified; 1. Air pressure is to use hydraulic press and air pressure machine to detect whether the steel pipe is leaking or air leaking, so as to ensure that the steel pipe is intact.

17. Packing and warehousing: 

The steel pipes that pass the inspection enter the finished product packaging area for packaging. The materials used for packaging include perforated caps, plastic bags, snakeskin cloth, wooden boards, stainless steel belts, etc. The outer surfaces of both ends of the wrapped steel pipe are lined with small wooden boards, and the outer surfaces are fastened with stainless steel belts to prevent contact between steel pipes during transportation and cause collisions. The packed steel pipes enter the finished product stacking area.

2) Processing technology of stainless steel seamless pipe

Several steps of stainless steel seamless pipe processing technology:

First, according to the customer's requirements, cut the stainless steel round bar into a specified length, then peel it on a lathe, and then drill a hole on a horizontal drilling machine. It is a small straight cylindrical hole. After the machining is completed, it has to be tested. According to the test results, the stainless steel ingot is ground to remove burrs, pull marks and small pits, etc., until it reaches the specified size and surface requirements. Then, according to the specification requirements of the product, the stainless steel ingots are sent to the corresponding processing location according to the price, such as the subsidiary steel rolling factory, waiting for the subsequent processing.

After the stainless steel ingot arrives at the steel rolling branch, the next work is to shape it according to the drawing size requirements. The specific operating procedures are roughly as follows: the first step is to heat and extrude first, then pickle after hot extrusion to remove the surface oxide layer. The second step is to carry out cold stretching (the number of stretching can be one time or several times, depending on the wall thickness of the seamless pipe), then pickling, and then heat treatment to eliminate The resulting material hardens; the requirement here is that every time it is stretched, a corresponding pickling and heat treatment must be carried out. The next step is cold rolling (cold rolling can be done once or several times, depending on the process requirements). Similarly, every time hot rolling is carried out, pickling and heat treatment must be carried out. The reason is also to remove The oxide layer on the surface of the material eliminates the material hardening caused by cold rolling.

It is worth mentioning that the times of cold stretching and cold rolling do not necessarily correspond one-to-one. It can be several times of cold stretching, or several times of cold rolling, or even only cold stretching without cold rolling, or only cold rolling without cold stretching, Depending on the specific situation of the product, the process is formulated and operated according to the process requirements. Furthermore, the commonality of the cold drawing and cold rolling of the manufacturers is that they can make the wall thickness of the semi-finished stainless steel seamless pipe thinner and increase the length. The difference is that the former operation is faster, but the one-time increase is relatively small; while the latter operation is more time-consuming, but the one-time increase can be more. The enterprise's cold drawing and cold rolling are all carried out on automatic equipment. The operator only needs to install the workpiece and adjust it, and then operate the control button, so the work efficiency is relatively high. The heat treatment is also automatic. The workpiece enters from one end of the furnace and exits from the other end, and runs continuously. The time is determined by the user's requirements for the product, wall thickness and material conditions. The fastest is less than 4~5 minutes. The slow ones are more than 7~8 minutes.

The stainless steel seamless pipe processed according to the above-mentioned cold drawing and cold rolling can only be regarded as a semi-finished product, the precision level is very low, and often fails to meet the requirements of the user, such as uneven wall thickness and bumps If there are defects such as scratches, internal and external surface pull marks and spots or pits, they must be ground. The specific operation procedure is: first, inspect the stainless steel seamless pipes that are cold-drawn and cold-rolled, and then repair and grind the defective parts according to the inspection situation. Grinding form, for small-diameter thin-walled seamless pipes, mechanical integral grinding is usually used. For thick-walled seamless pipes with medium and large diameters, if there is an overall defect problem, mechanical grinding is used; if it is a local defect problem, manual grinding is used (this is more common), and manual tools For portable electric sanders and upside down sanders.

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