Before you start welding, pay attention to the following methods:
Check the surface condition of thin-walled stainless steel pipes. If the pipe or pipe has obvious welds, scale, or handling damage, you will need to start with a coarse abrasive and use more steps than if the material is in good condition. Each abrasive leaves a scratch that must be removed with a finer abrasive. Coarser abrasives remove material faster but leave deeper scratches than finer abrasives, so effective finishing is about using the appropriate abrasive at every step. If you want to achieve a mirror effect, then you need to proceed more carefully and deliberately than if you are aiming for a rough result.

Welding process steps
Step 1: Remove the weld
Welds can be removed using flip-top discs, discs, or quick-change cloth discs. The choice depends on the type of grinder and the life expectancy of the disc. Flap and fiber discs are available on electric and pneumatic right-angle grinders, while cloth discs are only available on pneumatic, high-speed vertical spindles.

Step 2: Align the grain
The key part of the second step is to produce directional scratches that match the original grain direction. For stainless steel plate processing, the operator must determine the drawing direction; for thin-walled stainless steel pipes, the common method is to grind parallel to the weld. Tool options include horizontal axis machines such as drum sanders with coated abrasive belts; high-speed air-operated mold grinders with flap wheels; and air-operated grinders with nonwoven wheels.

Step 3: Do some final surface preparation
For the final step, it is recommended to use the tool used in step 2 equipped with nonwoven abrasives. Nonwoven tapes are a combination of strong synthetic mesh and high-quality abrasives, bonded with an adhesive. The open structure and cushioning effect of the nonwoven material allow for an active cutting action and improved surface finish without loading. Aluminum oxide medium strip is recommended for No. 3 finish; No. 4 finishing is recommended on stainless steel. Blending is achieved by slowing down the sander and minimizing the overlap between the welded area and the original texture. As in step 2, the part shape or size may not allow for a belt sander. In this case, the nonwoven wheel can be used with the same abrasive and grit size to produce the desired finish.

If the thin-walled stainless steel pipe requires an even higher surface finish, No. 5 to 8, then step 3 can be adjusted using a finer grit size of non-woven media and, in some cases, by changing to silicon carbide. For refinishing applications, the same nonwoven abrasive can be used in hand pads.

Stainless steel pipe surface grade:
The thin-walled stainless steel pipe processing industry uses numbers and letters to define 13 stainless steel surface treatments. The first five, numbered 0 to 2, are mill surface treatments. The other eight are completed, numbered 3 to 10, for reference by steel producers, or stainless steel processing plants.
No. 0: Hot rolled and annealed
No. 1: Hot rolled, annealed, and passivated
No. 2B: Cold rolled, annealed, pickled, and passivated, additionally passed through highly polished rollers
No. 2BA: Bright annealing, similar to 2B, but with an additional step where the steel is annealed in an oxygen-free atmosphere
No. 3: Rough
No. 4: Brushed
No. 5: Satin
No. 6: Matte
No. 7: Reflective
No. 8: Mirror