Most tube milling defects are not mysterious. They come from a specific place in the line. If you know which station controls which attribute, you can inspect the right point instead of rejecting finished bundles and guessing.
This guide maps the five forming stations to the defects they control, then shows how each YH production flow adds or changes stations around them.
The five stations and what each controls
Every line, whatever the weld process, runs these five functions:
- Uncoil & level — coil is uncoiled, levelled and joined strip to strip, so the line keeps running between coils. This station controls continuity, not tube shape. A levelling setting that is too aggressive shows up later as inconsistent forming.
- Breakdown — the first forming passes bend the strip edges, and the roller profile here sets edge stress for the whole line. A poor breakdown profile cannot be corrected at the fin pass.
- Fin pass — fin-pass rollers close the strip into an open round and guide the seam to the weld point. Seam misalignment at this station becomes a weld defect one station later.
- Welding — TIG, plasma, laser or high frequency closes the seam, and the route follows grade and wall thickness.
- Size & cut — sizing rolls set final diameter and roundness, then the saw cuts to length.
Note where roundness is set. It is the size station, not the forming section. Forming decides whether the strip can close cleanly; sizing decides the final dimension. The flow lists below group these functions under single step names — "forming" covers breakdown and fin pass.
How the six flows add or change stations
The five stations stay. What differs between lines is the stations placed between welding and cut-off.
Smart precision stainless steel line — 12 steps
Uncoiling, strip cleaning, feed guiding, forming, welding, internal seam levelling, wet grinding, primary sizing, online bright annealing, final sizing, servo cut-off, run-out table. Bright annealing sits between primary and final sizing, so the annealed tube is sized again before cutting. Wet grinding keeps the seam grinding station cool.
Laser precision line — 9 steps
Uncoiling, feed guiding, forming, laser welding, seam treatment, sizing, annealing, final sizing, cut-off. This is the shortest post-weld sequence: one seam treatment, one sizing pass, annealing, then final sizing.
The flow lists no separate grinding station; the brochure describes the laser bead as clean and narrow.
Industrial precision line — 14 steps
Uncoiling, feed guiding, forming, welding, internal seam treatment, external seam grinding, sizing, solution annealing, final sizing, straightening, eddy-current testing, inkjet marking, cut-off, run-out.
This flow treats both sides of the seam, adds a straightening step before testing, and tests every tube before it is marked.
Forming stands also use independent (asynchronous) pass adjustment to hold tolerance across pipe sizes, and cut-off is by circular saw.
Decorative stainless line — 8 steps
Uncoiling, brand printing, forming, welding, grinding, sizing & straightening, cutting to length, pipe collecting. Brand printing sits before forming, so the mark runs with the strip. Sizing and straightening are combined in one station.
Carbon steel HF mill — 14 steps
Coil loading, uncoiling, shear & butt weld, strip accumulator, feeding & leveling, forming, HF welding, bead removal, cooling tank, sizing, straightening, cut-off, run-out & packing, inspection & storage.
The accumulator keeps the line running through coil changes; bead removal and the cooling tank are specific to HF welding.
Large diameter line — 10 steps
Hydraulic uncoiling, leveling with shear & butt weld, powered guide, forming & welding, internal seam flattening, enclosed seam grinding, in-line black annealing, sizing & straightening, automatic cutting, product storage.
For Φ219–Φ630 mm pipe, the internal bead is flattened rather than merely levelled, and grinding is enclosed in a sealed box-type station.
Diagnosing a defect against the flow
Use the flow list as the diagnostic sequence. Ask where the attribute is last set.
- Roundness or diameter out of tolerance points to the final sizing station. On the smart line that is final sizing after annealing; on the industrial line it is final sizing after solution annealing.
- Seam appearance, inside or outside points to welding, then to the seam station after it: internal seam levelling or treatment, wet grinding, external seam grinding, or enclosed grinding. On the laser line, seam appearance is set at seam treatment only.
- A blackened or soft weld zone points to the annealing step. The smart line uses online bright annealing; the large diameter line uses in-line black annealing to restore ductility in the weld zone before sizing. Different result, different part of the flow.
- A raised internal bead on large diameter pipe is the special case: flattening is a dedicated station, and no other flow in the range names it.
This matters because a buyer comparing lines sees similar forming sections. The difference in finished tube quality is usually in the two or three stations after welding.
Which line carries which station
| Station after welding | Smart SS | Laser | Industrial | Decorative | HF | Large diameter |
|---|---|---|---|---|---|---|
| Internal seam levelling / treatment / flattening | Levelling | — | Treatment | — | — | Flattening |
| Seam treatment or external seam grinding | — | Seam treatment | Grinding | Grinding | Bead removal | Enclosed grinding |
| Annealing | Bright | Annealing | Solution | — | — | Black |
| Straightening | — | — | Yes | Combined with sizing | Yes | Combined with sizing |
| Eddy-current testing | — | — | Yes | — | — | — |
| Inkjet marking | — | — | Yes | — | — | — |
| Brand printing | — | — | — | Before forming | — | — |
| Strip accumulator and cooling tank | — | — | — | — | Yes | — |
Read the table as a checklist. If internal seam treatment is a requirement for your application, you need the industrial pipe and tube mill and its internal seam treatment step.
If you require eddy-current testing on every tube, only the industrial flow lists it. If your pipe is above Φ219 mm, internal seam flattening is specific to the large diameter tube mill.
To compare the stainless options side by side, start from the stainless steel tube mill category.
What to check during run-in and the first production week
Two flows already include instrumentation that cuts the diagnostic loop short.
On the industrial pipe and tube mill, eddy-current testing and inkjet marking sit before cut-off. A seam defect is caught on the tube and marked, so you can trace it back to welding or seam grinding on the same piece instead of finding it at final inspection.
On the smart stainless steel pipe line, weld defect detection is interlocked with the control system: fault alarms, auto stop and fault logging up to 2,000 records.
During run-in, that log is the fastest way to see whether faults cluster around one station — typically a breakdown or fin pass setting that needs adjustment.
For both, the practical routine is the same: keep the first week's fault log or test marks, match each fault to its station, and adjust that station before the run is accepted.
Next step
Tell us the pipe diameter, wall thickness and material, plus the post-weld stations your application needs, whether that is internal seam treatment, bright or black annealing, or eddy-current testing.
We will match your specification to the flow that already carries those stations. Send your requirements through the contact page.