Lap Joint Flange Carbon Steel — Factory Direct Supplier | Huaxia-Steel

A lap joint flange is a two-component flange system consisting of a flat flange with a rounded bore (the lap joint flange itself) and a separate stub end that is butt-welded to the pipe. The flange slips over the stub end and is free to rotate, which simplifies bolt-hole alignment during installation. Lap joint flanges are ideal for systems requiring frequent dismantling, stainless-clad piping or large-diameter lines where the flange does not need to be the same material as the pipe. Huaxia-Steel manufactures lap joint flanges in carbon steel to ASME B16.5 and EN 1092-1 standards.

Product Specifications

Parameter	Specification
Standard	ASME B16.5, EN 1092-1 Type 01 (plate flange)
Flange material	ASTM A105 (forged carbon steel)
Stub end material	ASTM A234 WPB, A105, or stainless steel
Size range	1/2″ to 24″ (DN15 to DN600)
Pressure class	Class 150, 300, 600
Face type	Flat Face (FF) or Raised Face (RF) on stub end
Manufacturing method	Forged (A105) or machined from plate

Available Grades

Component	Grade	Application
Lap joint flange	ASTM A105	Standard carbon steel backing flange
Lap joint flange	Q235 / Q345	Chinese standard backing flange
Stub end (Type A)	ASTM A234 WPB	Butt-weld carbon steel stub end
Stub end (Type A)	ASTM A105	Forged stub end for high pressure
Stub end (Type B)	Stainless 304/316	For corrosive service with CS backing flange

Dimensional Reference (ASME B16.5, Class 150)

NPS	Flange OD (mm)	Flange Thickness (mm)	Bolt Circle (mm)	Bolt Holes
2″	152	19	121	4 × 19 mm
4″	229	24	191	8 × 22 mm
6″	279	26	241	8 × 22 mm
8″	343	29	298	8 × 22 mm
12″	483	32	432	12 × 25 mm

Manufacturing Standards

• ASME B16.5 — Pipe flanges and flanged fittings, covers lap joint flange dimensions.
• ASME B16.9 — Butt-welding stub ends (Type A short pattern, Type B long pattern).
• MSS SP-44 / ASME B16.47 — For large-diameter lap joint flanges above 24″.
• EN 1092-1 — European standard for steel flanges (plate type 01).

Applications

• Frequently dismantled piping — the free-rotating flange makes bolt alignment easy, reducing maintenance time.
• Stainless-lined systems — use carbon steel backing flange with stainless stub end to save cost while maintaining corrosion resistance at the wetted face.
• Large-diameter lines — at 14″+ sizes, lap joint flanges are often cheaper than weld neck flanges.
• Aligner or swivel applications — the flange rotates to accommodate misaligned bolt holes in field piping.
• Marine and offshore piping — ease of assembly in confined spaces with limited tool access.

Quality Assurance

• Forged flange blanks from certified A105 material with traceable heat numbers.
• Stub ends hydrostatically tested to 1.5 × design pressure.
• Dimensional inspection of bore radius, bolt circle and flange face flatness.
• Hardness test on flange and stub end per ASTM specification.
• EN 10204 3.1 / 3.2 MTC supplied with every delivery.
• Optional NACE MR0175 compliance for sour service on request.

Packaging and Shipping

• Flanges and stub ends packed separately on wooden pallets with rust-preventive oil.
• Each component marked with size, class, grade, heat number and standard.
• Fumigated wooden packaging (ISPM-15) for export compliance.
• Container loading: 12 – 20 MT per 20′ container depending on size mix.

Get a Quote on Lap Joint Flanges

Huaxia-Steel supplies lap joint flanges in forged carbon steel (A105) with matching butt-weld stub ends (A234 WPB) in sizes 1/2″ to 24″. We offer Class 150 / 300 / 600 with FF or RF faces and full EN 10204 3.1 / 3.2 MTC. Stainless stub ends and NACE-compliant options are available. Contact us for a competitive quote.

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