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Lap Joint Flanges

A lap joint flange is never welded to the pipe. It rotates freely behind a stub end or a flat welded collar, which carries the sealing face, so the bolt holes can be swung into line after fit-up and the flange steel can differ from the wetted steel.

  • Rotates behind a stub end or flat welded collar
  • ASME B16.5 · EN 1092-1 Type 02 and 04 · your drawing
  • Carbon · low-temperature · stainless · duplex
  • MTC 3.1 for each part · dimensional report
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Lap Joint Flanges Explained

Dimensions follow ASME B16.5 lap joint practice, the EN 1092-1 type 02 and type 04 loose-plate types, or your drawing. Because the flange never touches the medium, it is commonly carbon steel over a stainless or lined stub end, which is the usual reason for choosing the type at all. Low-temperature, stainless and duplex flange grades are supplied where the project requires matched materials.

Two things decide the quotation: whether the stub end or collar is in our scope or yours, and the bore clearance over the stub-end barrel. The stub end or collar provides the gasket-contact surface; the loose flange provides the bolt-hole pattern and transmits bolting load. Confirm the rating or PN and compatibility of the complete assembly. Documents are MTC 3.1 for each part supplied, a dimensional report, and any NDT the project adds.

Engineering Snapshot

Product family: Flanges

Lap Joint Flanges Supply Scope

Lap Joint flanges rotate freely behind a stub end, which makes bolt-hole alignment easier. Related loose-flange systems use a compatible collar or flared pipe end; quote each system to its governing standard or drawing.

  • ASME B16.5 Lap Joint flange and stub-end review
  • Loose-flange arrangements over a collar or flared pipe end reviewed to their own standard
  • Carbon, low-temperature, stainless and duplex steel grades
  • MTC 3.1, dimensional report and NDT stated before quotation
Request a quoteInspection Documents

Lap Joint Flanges Technical Specification

Lap Joint Flanges Technical Specification
Scope and rating
Technical basisThis product is reviewed against its drawing, standard, material grade, quantity, inspection requirement and destination country.
Standards and materials
Standards / drawings
  • Project drawing or purchase specification
  • ASME B16.5 where flange dimensions follow ASME classes
  • EN 1092-1 / DIN where PN and DN requirements are specified
  • GOST 33259, 12820 or 12821 where CIS project requirements apply
  • ASTM, EN or project material standards as listed in the RFQ
Material grades
  • ASTM A105 carbon steel
  • ASTM A350 LF2 low-temperature carbon steel
  • Stainless steel grades such as 304, 316, 321 or 347
  • Duplex and super duplex grades when specified by the project
  • Alloy steel or drawing-specified grades subject to feasibility review
Geometry, tolerance and inspection
Product-specific differenceThe RFQ must define the dimensions and tolerances unique to Lap Joint Flanges rather than relying on a generic forged flange description.
Inspection depthMTC 3.1, dimensional report, heat-treatment record, PMI and NDT are confirmed according to project requirement.
Reviewed before quotation
  • Size, DN or NPS
  • Pressure class or PN rating
  • Drawing revision and critical dimensions
  • Facing, bore, bolt pattern and machining tolerance
  • Quantity, destination country and packing requirement
Buying logic
Best-fit RFQBest where bolt alignment, frequent dismantling or alloy cost saving over stainless stub ends drives the design.
Buyer applicationStainless and lined lines, water and utility systems, frequently opened piping and distributor stock.
Download this table as PDF Request a quote

Your standard, drawing revision and project specification govern.

Also known as

lap joint flangeloose flangebacking flangeEN 1092-1 type 02 / 04 flange

How to Send This RFQ

Send these details

  • Standard or drawing
  • Size / DN / NPS
  • Pressure class / PN
  • Material grade
  • Facing
  • Bore
  • Quantity
  • Heat treatment
  • Inspection requirement
  • Destination country
  • Third-party inspection need

Avoid these omissions

  • Sending a product name without standard, drawing or pressure rating
  • Leaving bore, facing or bolt pattern unclear
  • Mixing DN, NPS, PN and class references without a drawing
  • Omitting inspection documents until after price discussion
  • Forgetting destination country, packing or third-party inspection requirements

Manufacturing and Inspection Route

We confirm each step against your drawing or standard before we quote.

  1. Material review

    Material grade, heat number, certificate basis and substitution limits are checked against the Lap Joint Flanges drawing or standard before procurement is released.

  2. Forging process confirmation

    The forging route is selected around flange type, section thickness, bore allowance, hub or neck geometry and pressure-service requirements.

  3. Heat treatment

    Heat treatment is planned with the required record package, mechanical testing basis and impact-test condition where low-temperature or alloy service applies.

  4. Rough machining

    Rough machining opens reference faces, bore, hub, neck or sealing-face stock needed to control allowance before final flange machining.

  5. Final machining

    Final machining controls facing, bore, bolt pattern, groove, sealing surface and flange-table or drawing tolerances before dimensional inspection is issued.

  6. Inspection and document review

    Inspection covers dimensional report, MTC 3.1, PMI and required UT, MT or PT records before the release documents are matched to the purchase order.

  7. Marking, packing and export document preparation

    Marking, packing and export documents are prepared by PO line item so the Lap Joint Flanges shipment can clear customs and be identified at site receiving.

Inspection and Documents

List document requirements in the first RFQ; they affect price and schedule.

  • MTC EN 10204 3.1
  • Heat treatment record
  • Dimensional report
  • PMI when alloy verification is required
  • UT, MT or PT when specified
  • Tensile, impact or hardness test records when required
  • Third-party inspection support by project request

FAQ

What is the difference between a lap joint flange and a slip-on flange?

A slip-on flange is welded directly to the pipe. A lap joint flange is not welded at all: it rotates freely behind a stub end or flat collar that carries the sealing face, so bolt holes can be aligned after fit-up and the flange material can differ from the wetted material.

When are loose flanges the economic choice?

On stainless or lined lines, a carbon-steel loose flange over a stainless stub end saves alloy cost; and on lines that are dismantled often, the rotating flange speeds up bolt alignment.

What must an RFQ state for lap joint or loose flanges?

Standard (ASME B16.5 lap joint or EN 1092-1 type 02/04), size and rating, whether stub end or collar is included, material grades for each part, quantity and document scope such as MTC 3.1.

ASME B16.5 Flange Dimensions

ASME B16.5 flange dimensions for weld neck, slip-on, socket weld, lap joint and blind flanges, Class 150 to 2500, NPS 1/2 to 24, on a 3D section model.

Weld Neck vs Slip-On Flanges

Weld neck vs slip-on flanges to ASME B16.5: the same drilling and face, a different hub and bore. NPS 2 Class 600 compared with our weld neck drawing.

Forged Flange RFQ Checklist

Prepare forged flange RFQs with standard, size, class, material, facing, inspection and destination, plus fields for rings, cylinders and custom forgings.

EN/DIN vs ASME Flanges

EN 1092-1 and DIN vs ASME B16.5 (ANSI) flanges: DN/PN against NPS/Class, why DN 100 PN 16 will not bolt to NPS 4 Class 150, and the PED material scope.

Blind Flanges

Forged blind flanges NPS 1/2–60 to ASME, EN 1092-1, DIN or GOST, RF/FF/RTJ, in A105, LF2, stainless or duplex. MOQ 1 piece; mixed line lists welcome.

Ring Flanges

Send RFQs for ring flanges and forged ring blanks by drawing, OD, ID, height, material, machining allowance, heat treatment and inspection.

Long Weld Neck Flanges

Long weld neck flanges whose extended barrel is the vessel nozzle, forged to your drawing: overall length, neck OD and bore, ASME Class 150 to 2500, MTC 3.1.

High Pressure Flanges

High-pressure flanges by standard: ASME Class 600–2500, EN PN 100–400, JIS 30K–63K, GOST PN 100–250 - ring-joint grooves, hardness and ordered NDT.

ASME B16.5 Flanges

ASME B16.5 weld neck, slip-on, blind, socket weld, threaded and lap joint flanges, NPS 1/2 to 24, Class 150 to 2500, in A105, LF2 and stainless, with MTC 3.1.

GOST Flanges

Send GOST flange RFQs for Russian and CIS projects with DN, PN, material, drawing, inspection and export document requirements.

Commercial terms

Reply time
We reply to every RFQ within 8 hours.
Service hours
08:00–20:00 Eastern Time (ET; UTC−5, UTC−4 in summer), every day, including public holidays.
Minimum order
1 piece
Samples
Free of charge; you pay the freight.
Lead time
9 to 30 days after drawing approval.
Payment
30% deposit with the order; the balance is paid in full when the goods arrive at the port in China that you designate. The same applies to FOB, CFR and CIF.
Packing
Surfaces are coated with anti-rust oil. Most orders go in wooden cases, and every wooden case is fumigated. Large parts are steel-strapped onto pallets and wrapped in waterproof tarpaulin.
Quality claims
After you report a problem, we give you a handling plan within 8 hours.
Delivery terms
Standard: FOB the Chinese port you designate, Incoterms® 2020; we usually ship from Tianjin. On request: CFR or CIF to your destination port, quoted per RFQ. Other Incoterms® 2020 terms, except EXW and DDP, are quoted on request.

Send your RFQ or drawing directly to BLD Forge Direct.

Email quote@bldforgedirect.com with standard, drawing, material, quantity and inspection requirements.

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