The socket does three jobs at once: it aligns the pipe square to the fitting, it guides the weld, and it backs the joint with a machined shoulder. The pipe is inserted, pulled back about 1.5 mm from the socket bottom to allow thermal expansion, and fillet welded around the hub. The result is a joint with a smooth internal bore, no internal weld protrusion, and fatigue performance far beyond a threaded joint of the same size.
Our own catalogue shows the pattern at its typical scale: a 3/4 inch 90° elbow, Class 3000, socket weld, in A105. That elbow is the socket weld catalogue execution referenced on this site; any other socket weld type is assessed against your enquiry for the specific product before order.
| Item | Range / Options |
|---|---|
| Standards | Confirmed per product at enquiry — the catalogue execution referenced on this site is a 3/4 inch, 90 deg, Class 3000 socket weld elbow in A105 |
| Types | 90 deg elbows (catalogue execution: 3/4 inch, Class 3000, socket weld, A105) |
| Size range | Confirmed per product at enquiry — catalogue execution: a 3/4 inch Class 3000 socket weld elbow in A105 |
| Pressure classes | Class 3000 in the catalogue execution; further classes confirmed per product at enquiry |
| Socket bore | Machined to the pipe OD and schedule series of the class |
| Materials | Carbon steel ASTM A105 in the catalogue execution above; further grades confirmed per product at enquiry |
Where Socket Weld Wins
Small lines that must not leak and must not loosen: steam and condensate, boiler auxiliaries, hydraulic power lines, instrument air and gas, chemical dosing, and compressor and pump auxiliaries subject to vibration. In these services the fillet-welded socket outperforms threads on every axis except dismantling — a socket weld joint is cut out, not unscrewed.
The Crevice Question
The socket root leaves a small crevice between pipe end and socket bottom. In most industrial services that is irrelevant; in some corrosive and high-purity services the crevice is excluded by specification, and butt weld or special crevice-free designs are required. If your service is crevice-sensitive, say so on the enquiry — it changes the joint recommendation, and it is cheaper to learn that at quotation than at inspection. The wider comparison sits in our butt weld vs socket weld guide.
Ordering
Type, NPS, class and grade define the fitting; no schedule is needed because the class system already encodes the matching pipe series (Class 3000 with Sch 80 / XS, 6000 with Sch 160, 9000 with XXS). Unions add a seat material question only where specified.
Frequently Asked Questions
Which pipe schedule matches each socket weld class?
Class 3000 socket weld fittings pair with Schedule 80 / XS pipe, Class 6000 with Schedule 160, and Class 9000 with XXS. The socket bore is machined for the pipe OD, which is constant across schedules — the class selects the fitting's pressure capability.
Why is an expansion gap left before welding?
The pipe is backed off about 1.5 mm from the socket bottom so that when the line heats up, the pipe end does not bear on the socket and stress the fillet weld. It is standard socket weld practice and the socket depth assumes it.
Can socket weld fittings be hydrotested like butt weld?
Yes — a socket weld system is a welded pressure boundary and is tested with the line in the normal way, unlike threaded joints which many specifications test differently or restrict.
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Send Your Specification
Tell us the size, schedule or pressure class, material grade and quantity for the socket weld fittings you need. MOQ and lead time are confirmed in the quotation for your exact specification.