Orbital welding is automated GTAW where the torch rotates around a stationary tube under programmed control. The same arc current, travel speed, pulse profile and shielding-gas timing repeat joint after joint. You get X-ray quality on tubing too small to hand-weld reliably and on joints where the cost of one defect is much higher than the cost of the machine.
What the brochures do not tell you is that orbital welding works only as well as the tube prep walking in. A clean orbital head on a poorly squared tube produces bad welds at high speed, very consistently. Most “orbital welding doesn’t work for us” calls I have taken trace back to the prep, not the welder.
Here is how the process works and where the upstream decisions matter.
What “closed head” means
A closed-head orbital welder fully encloses the joint inside an inert-gas chamber. The tungsten electrode sees only argon — no oxygen, no moisture, no atmospheric contamination at the arc. The result is a weld with no oxide colouration on either the OD or ID face, which is the requirement for semiconductor UHP gas, pharmaceutical WFI and ASME BPE sanitary lines where any oxide can shed particles or contaminate the process.
The M200 family and most modern high-purity orbital systems are closed heads. Typical OD range per head: 3 to 50 mm depending on the model.
For larger pipe (above ~75 mm OD) the process moves to an open-head orbital welder — same logic, external shielding shroud, rotating torch. Used for larger process piping where the absolute contamination requirement is lower.
The four control variables
Every orbital weld program defines four things, and the program library is where the real value of an orbital system sits:
- Arc current, usually stepped or pulsed around the tube circumference so the puddle stays consistent in the 6-o’clock (gravity-against) and 12-o’clock (gravity-with) positions.
- Travel speed, the head rotation rpm, which defines heat input per unit length.
- Pulse profile, the peak / background current ratio and timing, critical on thin walls where heat input must be tightly controlled.
- Pre-purge and post-purge gas, the argon flow timing inside the head and inside the tube. Insufficient pre-purge leaves residual air and produces oxide; insufficient post-purge lets the cooling joint pick up atmospheric oxygen.
A qualified program for 6 mm OD × 0.9 mm wall 316L is not the same program as 12 mm OD × 1.5 mm wall — and not the same again for duplex, or for Inconel. Spend the time qualifying programs for the exact tube spec you actually weld, not the closest match in the library.
Where orbital welding is the standard
| Application | Why orbital is mandatory |
|---|---|
| Semiconductor UHP gas distribution | SEMI F70/F78 + zero contamination tolerance |
| Pharmaceutical / biotech process tubing | ASME BPE; CIP/SIP cleanability |
| Aerospace fluid systems (hydraulics, fuel, O₂) | Inspection rate too high for manual |
| Instrumentation tubing in refineries | Joint count makes economics work |
| Cryogenic and high-vacuum lines | Hand-weld defect rate unacceptable |
In every one of these, hand GTAW is technically possible. The defect rate at the volume required makes it uneconomic, and the manual welder talent pool that can hold the quality is shrinking globally.
Tube prep — the part that decides whether orbital pays back
Three prep parameters control whether the orbital weld holds quality:
1. Squareness of the tube end
The closed head clamps on the OD and the electrode sits on the joint centreline. If the tube end is not square to ≤ 0.05 mm perpendicularity, the arc gap varies through the rotation. The weld either burns through on one side or fails to fuse on the other.
A bandsaw cut is not square enough. An abrasive disc cut is not square enough. A hand-filed end is definitely not square enough.
The right prep is a pipe / tube facing machine sized for the OD range, with a calibration certificate per unit and controlled feed.
2. Cleanliness of the OD sealing area
The orbital head clamps on the tube OD. If there is a scratch, a fingerprint, a film of cutting oil, the seal is imperfect and air enters the inert chamber during the weld. Result: oxide on the weld.
Clean the OD with lint-free wipe and IPA before clamping. Handle the clamped section with gloves only. The standard contamination test in a UHP fab is a black-light inspection — anything that glows is a problem.
3. Squareness of the cut to the axis (no taper)
Some cutting methods produce a tapered cut that visually looks square but actually has 1 or 2 degrees of taper through the wall. On thin-wall tubing this is enough to vary the wall presented to the arc around the circumference, which varies heat input requirement, which varies weld quality.
The same cold-machining principle from cold cutting vs hot cutting applies — mechanical chip removal with a fixed cutter path produces the only consistent squareness.
How to size an orbital system
Three numbers fix the head selection:
- OD range of the tube mix
- Wall thickness — thin wall (≤ 1 mm) uses pulsed programs at ≤ 40 A; heavier walls use stepped DC up to ~120 A
- Material — 300-series stainless, duplex, Inconel, titanium each use a different program library and electrode
A common mistake: buying a head sized for the largest tube in the job mix, then forcing it to weld the small tubes too. A head’s effective range is narrower than its OD range — small tubes in a large head mean low torque control and poor finish. Mixed-OD jobs sometimes need two heads.
Three failure patterns I see
1. Orbital with non-orbital prep
A client invests in an orbital system, keeps the existing bandsaw for end prep, and cannot understand why the weld quality is no better than before. The orbital is doing its job; the bandsaw is sabotaging it. The prep machine matters as much as the welder.
2. Skipping pre/post-purge qualification
The program library defaults are fine for a generic setup. They are not fine for your specific tube length and fixture configuration. The pre/post-purge time has to account for the actual gas volume to be displaced and the actual cooling time of your joint. Run a small qualification block at install.
3. Sharing tooling and consumables with non-purity work
Tungstens, gas hoses, even purge fixtures used on shop carbon-steel work and then on UHP tubing carry contamination across. Dedicated consumables for the purity work — same colour-coding logic as stainless beveling tooling.
What this means for procurement
If you are evaluating orbital welding for a new line, budget the prep machine alongside the welder, not after. The pipe facing machine and the orbital welding system are a matched pair — they have to share OD range and have to be specified together.
Send the tube OD / wall / material mix and we will quote the matched prep + weld package — quote form.
About the author — Dongmei Guo is founder of Kedes Machine. On the shop floor since 2010, she builds portable on-site machining and cold cutting equipment in Shenzhen and works directly with field crews in oil & gas, power, shipbuilding and high-purity tubing. She writes here when a question comes up on the workshop floor that is worth answering in full.