Lap Joint Flange Carbon Steel — Factory Direct Supplier | Huaxia-Steel
A carbon steel lap joint flange—used in combination with a stub end—provides a cost-effective solution for piping systems requiring frequent dismantling for inspection, cleaning, or rotation. Unlike weld-neck or slip-on flanges, the lap joint flange itself does not contact the process fluid; the stub end forms the sealing face. This design allows the flange to rotate for bolt-hole alignment and to be reused across multiple stub-end replacements. Huaxia-Steel manufactures lap joint flanges in ASTM A105, A350 LF2, and stainless-steel-backed configurations from Class 150 to Class 600.
Product Overview
The lap joint flange consists of two separate components: a loose backing flange and a short-length stub end that is butt-welded to the pipe. The flange slides over the pipe and bears against the back of the stub end. Because the flange does not weld to the pipe, it can be made from lower-grade or different-material steel than the stub end, offering material savings in large-diameter or corrosion-resistant systems.
Specifications
| Parameter | Standard / Range |
|---|---|
| Size Range | ½” (DN15) – 24″ (DN600) |
| Pressure Class | Class 150, 300, 600 (ANSI B16.5) |
| Flange Material | ASTM A105, A350 LF2, SS304/316 (backing) |
| Stub End Material | ASTM A105, A350 LF2, A182 F304/F316 |
| Face Type | Flat Face (FF), Raised Face (RF) |
| Coating | Black paint, rust-preventive oil, hot-dip galvanized |
Dimensions (ANSI B16.5 Class 150, Selected Sizes)
| NPS | OD (mm) | Thickness (mm) | BC (mm) | Hole Qty |
|---|---|---|---|---|
| 2″ | 152.4 | 19.1 | 120.7 | 4 |
| 4″ | 228.6 | 23.9 | 190.5 | 8 |
| 6″ | 279.4 | 25.4 | 241.3 | 8 |
| 8″ | 342.9 | 28.6 | 298.5 | 8 |
| 10″ | 406.4 | 30.2 | 362.0 | 12 |
| 12″ | 482.6 | 31.8 | 431.8 | 12 |
Manufacturing Standards
- ASME B16.5 – Pipe Flanges and Flanged Fittings (NPS ½”–24″)
- ASME B16.47 Series A/B – Large Diameter Steel Flanges (NPS 26″–60″)
- EN 1092-1 – Circular Flanges for Pipes, Valves and Fittings (Type 37)
- MSS SP-44 – Steel Pipeline Flanges
Applications
- Process piping requiring frequent dismantling (food, pharma, chemical)
- Systems with exotic stub-end materials and carbon-steel backing flanges
- Large-diameter pipelines where bolt-hole alignment is critical
- Piping subject to erosion or corrosion at the joint (easy stub-end replacement)
- Cost-sensitive projects using lower-grade backing flanges
Quality Assurance
All lap joint flanges are visually inspected for surface defects, and dimensions are verified against B16.5 tolerance tables. Stub ends undergo ultrasonic testing (UT) on the weld neck for lamination and crack detection. Hardness testing and chemical spot analysis are performed on every heat lot. Third-party inspection by TPI agencies (SGS, BV, DNV) is available on request.
Packing and Shipping
Flanges are packed in wooden crates or plywood pallets, separated by cardboard sheets to prevent face damage. Stub ends and flanges are matched and labeled by heat number and size. Rust-preventive oil or VCI film is applied for ocean transit. Each package includes a packing list, mill test certificate, and dimensional inspection report.
Order Lap Joint Flanges with Stub Ends
Need ASTM A105 lap joint flanges matched with Type A or Type B stub ends? Send us your size, pressure class, and material specification for a competitive factory-direct quotation.
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