PROCESS FLOW CHART OF SEAMLESS STAINLESS STEEL PIPES

 

All the steps have been explained in detail below:

1. Round Bar Selection

This is the first step towards manufacturing seamless products at Xintongda. We select a strong round bar or a billet of the required grade. As we have to produce the products without any weld seams, we select the best round bars.

2. Re-inspection

Once we select the round bar, we send it for re-inspection to check the quality and purity of the bar.

3. Cut to Length

The round bar is then cut to a specific length or the maximum length as desired.

4. Centering

Centering is a step in which the bar’s axis is aligned with the plug before it is pierced. This step is crucial as the plug (the internal diameter of the pipe/ tube) should accurately correspond to the bar’s central axis.

5. Peeling

Peeling basically means to remove the outer surface of the bar or billet to avoid surface defects. In this process, cracks, scale, inclusions, or decarburised layers are eliminated from the billet.

6. Heating

The peeled bars are then sent for heating in a furnace. This process makes the bars soft, so that they do not crack when pierced.

7. Piercing

Piercing involves converting the round bar into a hollow shell by creating a hole. This is one of the most important steps.

8. Inspection

Once pierced, the hollow shells undergo inspection to check dimensional accuracy and defects. This step helps us to discard shells with issues and save time.

9. Grinding

This step removes surface irregularities and excess material by grinding. It is a key step to improve the surface finish and dimensional precision.

10. Pickling

Pickling involves treating the surface of the hollow shell with an acid solution to get rid of oxidation, scaling, rust, contaminants, and other impurities. This step makes the shell chemically prepared.

11. Inspection (Post-Pickling)

The hollow shell is again inspected after pickling for surface and dimensional quality. This step confirms that the earlier steps were successful.

12. Drying

Drying mainly refers to the process of removing moisture, coatings, or other unwanted residues that were left due to pickling or washing. Moisture can lead to corrosion, and hence drying is an important step.

13. Cold Drawing / Cold Rolling

In cold drawing, the hollow shell is pulled through a die over a mandrel to reduce its diameter, wall thickness, and improve its dimensional accuracy and surface finish. Cold rolling, on the other hand, is a similar process where the hollow shell is rolled on a two-roll mill at room temperature. Both processes provide similar results.

14. Degreasing

Degreasing is a cleaning process where lubricants, oils, greases, and fatty acids used during cold working are removed to make the surface clean.

15. Heat Treatment

The heat treatment step involves heating and cooling the hollow shell under controlled conditions. This step modifies the internal microstructure of the pipe/ tube and improves its mechanical properties.

16. Straightening

There is a chance that the hollow shell might bend, twist, or deform during cold rolling. In straightening, an external force is applied to straighten and remove such deforms. The product achieves proper alignment due to this step.

17. Fixed Length Cutting

The straightened pipe/ tube is cut to a length specified by the consumer or according to the application.

18. Pickling/ Passivation

Once the product is cut to a fixed length, it again undergoes pickling to remove any oxides or to improve its corrosion resistance. In passivation, the surface of the pipe/ tube is treated with an oxidant. This oxidation forms an oxide layer, which resists oxidation.

19. Inspection for Finished Products

After pickling, the product is sent for a final inspection to check dimensions, surface quality, and compliance with the international ASTM standards.

20. Marking

Once inspected, all the products are marked with relevant details, like grade, size, thickness, outer diameter, heat number, etc. Due to this, all our products are easily traceable.