Weld Seam Position in Stainless Steel Square Tube: What to Put on the Drawing

Quick answer: If the longitudinal mill weld can affect assembly, mark the permitted face and seam location on an end view. Identify the datum, set an allowable position band if the location matters within that face, and specify any limit on the internal bead separately. Check an actual mating part or an agreed gauge before releasing the full order.

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When the weld seam changes the fit

The mill seam runs along the tube where the formed edges were joined. A raised bead inside the tube can interfere with an insert or stop a splice plate from sitting flat. On the outside, the seam can fall on a visible face or cross a planned slot. A square tube can be turned 90 degrees and still fit the same fixture, so its outside dimensions alone do not tell an operator which face contains the seam.

Consider a frame leg with a slip-in leveling foot. If the foot contacts all four inner faces, moving the seam to a different face may leave the same interference. In that case, specify the required clearance and bead condition, then verify insertion to the full engagement depth. If the foot has a relief on one side, orienting the relief to the seam may solve the problem, provided the parts can be located consistently during assembly.

How to call out the seam on the drawing

1. Identify the face. On the tube end view, label the permitted face and show which end the view is taken from. Orient the faces to a feature, fixture or agreed reference mark. If any face is acceptable, say so.
2. Define the position band if needed. Dimension the seam centerline from a reproducible reference such as the theoretical intersection of two outside faces. Label that reference on the drawing so nobody measures from the edge of the rounded corner instead. Agree the allowable band and where along the length it applies.
3. Specify the bead separately. State the allowable internal projection if it affects clearance. Define the reference surface and how it will be checked. Record any outside appearance requirement separately from the inside bead.
4. Tell the next operator how to find it. If polishing or finishing makes the seam hard to locate from the outside, agree a temporary mark or other reference that stays identifiable through the required fabrication steps.

What to verify on the first piece

• Identify End 1 and Face B from the drawing or the agreed marks, then locate the seam. Check the position at the sections defined in the inspection plan.
• If the internal bead controls fit, check it with the agreed method. If you can see only the cut end, a measurement there does not establish clearance deeper in the tube.
• Try the mating part or agreed gauge to the required depth. Remove burrs only as allowed by the specification, and follow the agreed insertion method. For slotted or bent parts, verify orientation after the relevant operation as well.

Standards note. ASTM A554 covers welded stainless steel mechanical tubing, including square and rectangular shapes. Choose the specification for the intended service. If the assembly depends on a particular seam position, define it on the drawing and confirm that requirement on the order.

What to send with your RFQ

Send the grade, applicable specification, outside dimensions, wall thickness, finish, cut length and quantity. Attach the drawing revision showing the reference face, permitted seam band and any bead or fit requirement. If a proposed change in seam location would affect assembly, ask the supplier to flag it before you place the order.

For a grade and shape reference, see the 316 stainless steel square tubing page. In your inquiry, confirm the welded manufacturing route, applicable standard, seam position and internal bead limit for the specific order.

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