The system has two halves. The stub end — a short flared pipe piece — is butt welded to the line and provides the sealing face in the pipe's own material. The lap joint flange sits behind the flare and provides clamping force. Because the flange is not welded and not wetted, it is commonly carbon steel even when the stub end and pipe are stainless: the expensive grade is bought only where it works.
The second advantage shows up at installation. The flange rotates freely on the pipe, so bolt holes align with the mating flange by turning the flange, not by springing the pipe. On long runs and equipment tie-ins that saves real fitting time, and it is why lap joints are the default on lines that are dismantled for cleaning or inspection.
| Item | Range / Options |
|---|---|
| Standards | Confirmed per product at enquiry — the mating stub end is confirmed with the flange for the specific product |
| Size range | Confirmed per product at enquiry |
| Pressure classes | Confirmed per product at enquiry |
| Faces | The flange itself carries no sealing face — the stub end flare is the face; flange back face is flat |
| Materials | Flange grade confirmed per product at enquiry — carbon steel backing flanges are the common choice behind alloy stub ends. Stub end: matched to pipe grade |
| Requires | A stub end per joint — order the pair together |
Where Lap Joints Win
Stainless and alloy process lines (material saving), food, chemical and water lines that open for cleaning, and any joint where alignment of bolt holes on site is predictably difficult. The cost logic is strongest exactly where pipe material is most expensive.
Where They Do Not
Lap joint assemblies are not for severe bending loads, high classes beyond their working range, or services where the piping specification requires welded or RTJ joints. The sealing face is the stub end's flare, whose thickness is the pipe wall — the system is honest light-to-medium duty engineering, chosen for economy and maintainability.
Ordering the Pair
Order stub end and flange as a set: same NPS and class, stub end in the pipe grade and schedule, flange in the grade you choose for the backing. If you already have stub ends, send their dimensions with the enquiry — the flange bore must clear the pipe OD and its back face must suit the flare diameter, and the pairing is assessed for the specific product before order.
Frequently Asked Questions
Does the lap joint flange material have to match the pipe?
No — and that is the point of the system. The flange is not welded or wetted, so carbon steel backing flanges are standard behind stainless stub ends. Only the stub end must match the pipe.
Can lap joint flanges be used with RTJ faces?
No. The sealing face is the stub end flare, which suits flat and raised-face style gasketing. RTJ joints require solid flanges with machined grooves — see weld neck flanges.
Are lap joint flanges reusable?
Yes, the backing flange is usually the most reusable part on the line: unbolted, it slides back and can be refitted with a new stub end and gasket. That reusability is part of the economy.
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Send Your Specification
Tell us the size, schedule or pressure class, material grade and quantity for the lap joint flanges you need. MOQ and lead time are confirmed in the quotation for your exact specification.