Stainless Steel Weld Fittings

Stainless steel weld fittings are SS 316 connectors with a plain, square-cut weld end that is butt-welded to the tube, giving a permanent joint with no threads, ferrules or internal crevice. Vikay supplies male and female connectors, unions, reducing unions, union elbows and tees in fractional and metric tube sizes.

A butt-weld joint is specified where no mechanical leak path is acceptable: high-purity and semiconductor gas lines, high-vacuum systems, high-temperature service, and lines that will be radiographed or helium leak tested. The weld end is machined to a matched wall so the orbital or manual weld fuses without a filler step change, and the bore stays smooth and crevice-free.

The range covers male connectors (tube butt weld to male NPT), female connectors (tube butt weld to female NPT), union connectors, reducing unions, union elbows and union tees, in both fractional (1/8-1 in) and metric (3-25 mm) weld ends. Patterns combining a weld end with a twin-ferrule tube end or a threaded end let a welded run terminate in a serviceable connection at the instrument.

Fittings are machined from SS 316 bar to ASTM A276 / A479, with 316L available and generally preferred for welded work because the lower carbon reduces sensitisation and weld-decay risk. Weld ends are supplied clean and square. Specify tube outside diameter and wall thickness together, because a weld end must match the tube wall, not just its OD.

Frequently Asked Questions

When should I choose weld fittings over tube fittings?

Choose butt weld where the joint must be permanent and crevice-free: high-purity gas, vacuum, high temperature, radiographed lines, or any circuit where a mechanical joint is not permitted by specification. Choose twin-ferrule tube fittings where the line will be broken for maintenance or instrument changeout.

Should I specify 316 or 316L for welded fittings?

316L is generally preferred for welding. Its lower carbon content reduces chromium carbide precipitation at grain boundaries in the heat-affected zone, which is what causes weld decay and intergranular corrosion in service. State 316L on the enquiry if your weld procedure or specification calls for it.

Do the weld ends need to match my tube wall thickness?

Yes, and this is the most common ordering error. A butt weld fuses two matched sections; if the fitting wall and tube wall differ, the joint has a step that concentrates stress and complicates an orbital weld schedule. Give both outside diameter and wall thickness on your enquiry.

Are the fittings suitable for orbital welding?

The weld ends are machined square and to a consistent wall, which is what an orbital head needs to run a repeatable schedule. Confirm your required end preparation, surface finish and any sulphur-range requirement on the enquiry, since those are specified per project.

Can I get a fitting with a weld end on one side and a threaded end on the other?

Yes. Male and female connectors combine a tube butt-weld end with a male or female NPT thread, so a welded run can land on a threaded instrument port. Mixed weld-to-tube-fitting patterns are also catalogued.