What drives lap joint flange and stub-end pricing?

Pricing is driven by stub end material grade, pressure class & size, stub end pattern, certification level (3.1 vs 3.2), and machining extras & quantity.

What is the lead time for lap joint flanges?

Stocked standard rings and stub ends usually dispatch in 1 to 2 weeks. Special orders (alloy, non-standard thickness, third-party certification) typically require a 3 to 4 week production schedule.

Lap Joint Flange & Stub End Solutions ASME B16.5 / B16.9 Carbon, Stainless & Alloy

A lap joint flange is a loose backing ring that slides over a butt-welded stub end and rotates freely to line up the bolt holes — and because the flange itself never touches the process media, it lets you pair a low-cost carbon steel ring with the exact alloy your line needs only on the wetted stub end. Synbase Steel forges, machines and certificates lap joint flanges and matched Type A and Type B stub ends across every standard pressure class, each supplied with the material test certificate your inspector releases against.

Request an RFQ Quote

Lap Joint Flange and Stub End Solutions for ASME B16.5 / B16.9

1/2″–24″ Size range (NPS)

150–2500 Pressure class (lb)

Type A / B ASME B16.9 stub ends

CS · SS · Alloy A105 / A182 F304-F316L

EN 10204 3.1 MTC with every lot

100+ Export countries

How a Lap Joint Flange Works — The Two-Part Backing-Ring Design

A lap joint flange is one half of a two-part assembly. Its other half is a lap joint stub end, a short length of pipe that is butt welded to the line and machined with a flared sealing face — the lap. The loose backing flange drops over that stub end and is free to rotate, so a fitter spins the ring to align its bolt holes with the mating flange instead of cutting and re-welding to chase alignment during installation. Only the stub end is wetted; the backing ring sits behind the lap face and never sees the process fluid.

That single fact — the flange does not contact the media — is why engineers reach for this fitting in two situations. One is any piping system that is opened on a schedule for inspection, cleaning or catalyst change: the ring lifts straight off once the stub end is unbolted, so frequent disassembly does not mean cutting pipe. Another is a corrosive line where the pipe is an alloy: you weld an alloy stub end to match the pipe and back it with a cheap carbon steel ring, instead of buying a solid alloy flange.

The pain this design removes is real, and it is rarely the flange. On a fixed, welded hub a crew loses hours to bolt-hole alignment on every shutdown, and the gasket seating face is scuffed a little more each time the joint is broken and remade. A lap joint flange turns that repeated separation into a clean, quick lift-off — provided the stub end lap is flat, square and the right thickness. Get the stub end wrong and the saving evaporates, which is exactly why this page treats the stub end as a precision fitting.

Synbase Lap Joint Flange & Stub End Range — Materials, Classes & Faces

Each lap joint flange we deliver is either forged from the solid ASTM A105 (carbon steel), A182 (stainless & alloy steel) or cut from plate (in the largest diameters) and machined to ASME B16.5 so the bolt circle matches yours to within an nth degree. Its matched lap joint stub end is furnished to either ASME B16.9 (long pattern) or MSS SP-43 (short, light-wall) in the same grade, or higher alloy, as the ring. Since the ring and stub end are offered as a pair, the material cert covering the wetted stub end is what your metallurgist will be referring to.

Carbon Steel Lap Joint Flange

ASTM A105 · Class 150–2500 · RF/FF · 1/2″–24″

Stainless Steel Lap Joint Flange

A182 F304/F316/F316L · Class 150–1500 · RF

Lap Joint Stub End (Type A / B)

ASME B16.9 / MSS SP-43 · CS / SS / alloy

Alloy & Duplex Pair

Duplex S31803 · alloy stub end + CS ring

Because the fitting is sold as a package, the specification table below is organised by ring and matched stub end, each with its own pressure rating. An A105 Class 150 ring carries 285 psig non-shock service @ 100F (about 170 at 500F); Class 300 rises to 740 psi non-shock @ 100F (again, actual working temp dictates).

Component	Material grade	Standard	Class / pattern	Faces
Backing flange (ring)	CS ASTM A105 / A350 LF2	ASME B16.5	150–2500	RF / FF
Backing flange (ring)	SS A182 F304 / F316 / F316L	ASME B16.5	150–1500	RF
Lap joint stub end	CS A234 WPB / SS A403 WP304-316L	ASME B16.9	Long (ANSI) pattern	Machined lap, Type A/B
Lap joint stub end	SS light wall (Sch 5S/10S)	MSS SP-43	Short pattern	Machined lap

If your line is…	Stub end material	Ring material	Typical class
Water, air, low-pressure utility	CS A234 WPB	CS A105	150–300
Frequent dismantling for inspection	Match pipe grade	CS A105 (reusable)	150–600
Corrosive / chemical / hygienic	SS A403 WP316/316L	CS A105 or SS	150–600
Chloride / sour / offshore header	Duplex S31803	CS A105	300–900

The Cost Logic — Why Pair a Cheap Backing Flange with an Alloy Stub End

01 The Geometry — Where the Alloy Goes 02 The Saving — How Large It Gets

Commercially, the case for a lap joint flange rests on one geometry detail: only the stub end is wetted. On a solid weld neck or slip-on flange in a corrosive line, the entire forged flange has to be the alloy — every pound of it — even though only the bore touches the fluid. With a lap joint assembly you weld a small alloy stub end to the pipe and slide a plain carbon steel backing ring behind it. Expensive metal goes only where the corrosion is; the bulk of the bolted mass stays cheap. On a 316L or duplex line with many connections, that is the difference that pays for the joint.

How large are the cost savings? It depends entirely on the alloy premium and the number and size of the flanges, so any single percentage would be dishonest. What the industry does report is direction and magnitude: on large-diameter or multi-hundred-flange projects the saving from backing an alloy stub end with a carbon steel ring can easily reach into the tens of thousands of dollars across the bill of materials. There is a second, quieter saving as well — if a sealing face is ever damaged, you replace only the stub end, and a backing ring that passes inspection is reusable on the next assembly.

One trap procurement teams fall into is buying the ring carefully and the stub end carelessly. The backing flange is a commodity drilled to a standard — but the stub end carries the lap face, the lap thickness and the alloy that the joint actually seals and survives on. Cut the corner there and you save a few dollars on a fitting that then leaks or under-specs the wetted metal. Our next section is the one that keeps that from happening.

Alloy only where it is wetted

Pairing a carbon-steel backing flange with an alloy stub end keeps high-grade metal off the bolted ring entirely. On large or high-alloy bills of material, the saving versus solid alloy flanges is reported in the tens of thousands of dollars.

Direction and magnitude from industry RFQ experience (texasflange.com); exact saving depends on alloy premium, size and quantity — quoted per line list.

Want the saving sized for your project, not a generic claim? Send your line list for an itemised cost comparison. Request Comparison →

Lap Joint Stub Ends — Type A vs Type B, MSS SP-43 & ASME B16.9

“For lap joint assemblies, the stub end is where the game is won or lost – and selecting the wrong type of stub end from a vendor is the most common field error.”

Actually, Type A versus B isn’t long versus short, like you hear – that vendor’s description of the standard isn’t correct. It is the lap fillet radius. A Type A stub end is machine with a broad corner radius so it fits into the port of a true lap joint flange while a Type B stub end is machine with a very small radius designed to slip under a slip-on flange being used as backing. Get type B when it is backed by a slip-on; get Type A when it backed by a lap joint flange. There is another form, Type C, a flared (or Vanstone) stub end which is also has a rounded edge and is machine with a 75% wall lap thickness but left unmachined.

Stub end	Pairs with	Lap fillet radius	Lap face	Pattern / standard
Type A	Lap joint flange	Large (e.g. 3.05 mm @ 1/2″)	Machined, serrated	ASME B16.9
Type B	Slip-on used as backing	Small (0.76 mm)	Machined, serrated	ASME B16.9
Type C (flared)	Lap joint / van stone	Rounded ID edge	Unmachined	Flared, 75% wall
Short pattern	Light-wall SS pipe	per type	Machined	MSS SP-43 (Sch 5S/10S)

Two standards govern length and wall. ASME B16.9 is the long (ANSI) pattern; MSS SP-43 is the short pattern for light-wall stainless pipe, and its dimensions are substantially the same as B16.9 from NPS 1/2 to 24 except for the outside diameter at the weld bevel. As a worked example, a 1/2″ stub end is 50.8 mm long in the short pattern versus 76.2 mm in the long pattern — specify which your isometric assumes, because they are not interchangeable on a tight tie-in.

Engineering Note — Lap thickness only goes one way

The lap is the gasket-contact face, and its thickness must be at least the nominal pipe wall, with a tolerance of +1.52 mm / −0 — it may be thicker, never thinner. That “additional lap thickness” rule exists so the seating face always has enough metal after machining. The fillet radius carries its own tolerance (+0 / −0.76 mm up to 3-1/2″, +0 / −1.6 mm at 4″ and above), and the general wall stays at or above 87.5% of nominal. Quote the schedule of the mating pipe and we cut the stub end to suit it; we do not assume Schedule 40 and hope.

“When a lap joint ‘mysteriously’ leaks, the stub end is almost always the cause — a lap face that is not flat and parallel, a surface finish the gasket cannot seat on, or a lap thickness someone bought as a commodity. We machine and inspect every lap face to the standard before it leaves, because the ring is the easy part.”

— Synbase Steel Engineering Team, Flange & Forging Division

Not sure whether your assembly needs Type A or Type B? Send your flange detail for a stub-end match

Lap Joint vs Slip-On vs Weld Neck vs Van Stone — When to Use Which

A lap joint flange is the right fitting for a specific job, not every job, and the honest comparison is in behaviour, not adjectives. Its strengths are bolt-hole alignment by rotation, frequent disassembly without cutting pipe, and material economy on alloy lines. Its real limitation is fatigue: a lap joint assembly has low fatigue resistance, and in cyclic or vibrating service it is the base metal of the stub end — not the weld — that eventually fails, “like a coat hanger bent back and forth.” Where vibration is unavoidable, the joint should be upgraded to a butt-welded hubbed (weld neck) design. We would rather you knew that before the order than after the shutdown.

Requirement	Lap Joint	Slip-On	Weld Neck	Van Stone
Bolt-hole alignment	Rotates free	Fixed	Fixed	Rotates free
Frequent disassembly	Lift ring off	Cut to remove	Cut to remove	Lift ring off
Material economy on alloy lines	Alloy stub only	Whole flange alloy	Whole flange alloy	Alloy liner only
High-pressure / fluctuating load	Low fatigue life	~1/3 of weld neck	Best	Low fatigue life
Sealing-face exposure	Ring not wetted	Flange wetted	Flange wetted	Liner not wetted

Where does “van stone” fit? A van stone flange is the same idea as a lap joint flange — a loose ring rotating over a flared lap — and the term is most common in plastic, lined and HVAC duct piping; in steel pipework the two names describe the same fitting, and a swivel flange is a close cousin with a fully rotating ring. As a practical rule, use a slip-on for low-cost moderate-duty connections, a weld neck for severe or fluctuating loads, and a lap joint (van stone) flange where you need frequent disassembly or alloy economy and the service is steady. Tell us the service and we will tell you honestly if a lap joint is the wrong call.

Comparing flange types for a specific line? Request a flange-type recommendation with your line data. Request Recommendation

Dimensions & Standards — ASME B16.5 Class 150–2500 + B16.9 Stub Ends + DIN / EN / JIS

A lap joint flange is only correct when its outside diameter, thickness, bolt circle and hole pattern match the mating flange exactly — and because ASME B16.5 drilling is shared across flange types, the figures below are the same bolt circles your weld-neck and blind flanges use at each size and class. Our tables give the most-requested carbon-steel dimensions for the lap joint pattern; full charts for every class, plus the matched stub-end schedule, ship as the downloadable spec sheet. ASME B16.5 covers NPS 1/2 through 24; above that, large-diameter lap joint flanges move to ASME B16.47 Series A or B.

Synbase lap joint flange dimensional drawing

NPS	OD (O)	Flange thk (tf)	Bolt circle (BCD)	No. of bolts	Hole dia.
2″	6.00	1.00	4.75	4	0.75
3″	7.50	1.19	6.00	4	0.75
4″	9.00	1.31	7.50	8	0.75
6″	11.00	1.56	9.50	8	0.88
8″	13.50	1.75	11.75	8	0.88
10″	16.00	1.94	14.25	12	1.00
12″	19.00	2.19	17.00	12	1.00

NPS	OD (O)	Flange thk (tf)	Bolt circle (BCD)	No. of bolts	Hole dia.
2″	6.50	1.31	5.00	8	0.75
3″	8.25	1.69	6.62	8	0.88
4″	10.00	1.88	7.88	8	0.88
6″	12.50	2.06	10.62	12	0.88
8″	15.00	2.44	13.00	12	1.00
10″	17.50	3.75	15.25	16	1.12
12″	20.50	4.00	17.75	16	1.25

For NPS 26″–60″ the lap joint flange dimensions move to ASME B16.47 (Series A / Series B). Metric projects call up EN 1092-1 (PN6–PN40, Type 02 loose flange) or DIN 2642; Asian projects cite JIS B2220 (5K–20K). Each matched stub end follows ASME B16.9 (long pattern) or MSS SP-43 (short, light-wall pattern). We cross-reference your drilling standard and the mating pipe schedule at quotation so a DIN ring never meets an ANSI stub end.

Quality, Certification & Material Traceability

Nothing loses a week on site faster than a lap joint stub end that arrives without valid paperwork, because the stub end is the wetted, alloy-critical half of the assembly. Procurement teams tell us the same story: a supplier claims a grade, cannot produce a matching certificate at goods-in, and the whole lot is quarantined while the line stands idle. Synbase closes that gap at the source. Every shipment carries an EN 10204 3.1 Material Test Certificate – chemical analysis, mechanical properties and heat-treatment record verified by our works – with the heat number punched on the fitting so the stub end in the inspector’s hand traces back to the mill melt that cast it. Where the project demands it, we arrange EN 10204 3.2 certification witnessed by a third party such as SGS, BV or TÜV.

EN 10204 3.1 MTC every lot

ISO 9001 Quality management

ISO 14001 Environmental

ISO 45001 Occupational H&S

CE / PED EU pressure

Synbase is the dedicated flange business of the E-CHENG STEEL GROUP, which forges, heat-treats and machines pipes, fittings, flanges and valves on its own bases rather than trading unmarked stock from someone else’s yard. Our raw material comes direct, under long-term supply contracts with China’s largest steel producers – Baosteel, Tianjin Pipe (TPCO), Ansteel and TISCO – and the group is a member of the China Iron and Steel Association. It is that unbroken line – from mill of record, to in-house forge, to heat numbers stamped on each ring and stub end, to a 3.1 certificate – that lets your QA department release the parts without retesting.

Procurement Tip — Three checks before you bolt up

A counterfeit mill test certificate is a real risk in the fittings market. When your parts arrive, make three checks: the heat number stamped on the flange and stub end must match the heat number on the 3.1 certificate; the certificate must list actual measured test values, not merely the words “meets spec”; and you must be able to verify the issuing works. Genuine paperwork passes all three – request a sample from us and run the checks yourself.

Want to see our documentation before committing?

Request a sample EN 10204 3.1 Material Test Certificate →

Procurement Guide — MOQ, Lead Time, Custom Stub-End Machining & Global Shipping

Unit price is the least useful number when you cost a lap joint flange order. What decides the real spend is total landed cost - the rings and stub ends, the certification, duties, export packing, and the cost of schedule risk if a non-conforming shipment has to be re-inspected or remade. A common procurement mistake is reading a low unit price as a saving, then paying it back several times over when a mismatched stub end or a missing certificate stalls the tie-in.

Regarding lead time, the real benchmark is that for stocked standard rings and stub ends they usually dispatch in 1 to 2 weeks, whilst for a special order pair - be it alloy stub end, non-standard lap thickness or third party certification, you will be looking at a typical 3 to 4 week production schedule to include sourcing material, forging, heat treatment and machining. We manufacture and control the full steel-to-fitting process in-house and maintain sufficient billet stocks in common A105, 304 and 316 materials, ensuring machining starts immediately with the purchase order instead of waiting for a mill confirmation. We supply to national oil companies, EPC contractors and a distributor network covering Southeast Asia, the Middle East and Europe and every single order ships out with a tracing report, from works to port. Whether you need one critical spare or the full project bill of materials - the order size is yours to command - send across the requirement and we will work to engineer the quotation around it.

What drives your quotation

Lap joint flange and stub-end pricing moves with a handful of physical characteristics, so you can tune the RFQ to your budget once you know which lever you are pulling. Our table lists them without a number attached, because the number is a property of your specific line list.

Cost driver	How it moves price
Stub end material grade	CS baseline; SS 304/316 higher; duplex/alloy highest — and it is the wetted, alloy-critical half
Pressure class & size	Higher class and larger NPS = more forged mass in the ring
Stub end pattern	ASME B16.9 long vs MSS SP-43 short; flared Type C; non-standard lap thickness
Certification level	3.1 standard; 3.2 third-party witnessing adds time and fee
Machining extras & quantity	Special facings (tongue-and-groove, male-and-female), volume lowers unit cost, seaworthy crating itemised

Ready to price your line list? Request an RFQ quote with itemised landed cost →

Lap Joint Flange Engineering & Optimization Tools

Lap Joint Flange FAQ

What is another name for a lap joint flange?

Another common name for the lap joint flange is a loose flange, backing flange, swivel flange, van stone flange or lap joint ring flange, often abbreviated to LJRF. In plastic, lined and HVAC duct piping, you will most frequently hear the term ‘van stone’ whilst in steel piping, any of those are used interchangeably and all describe the same loose ring that turns about a butt welded stub end. A rolled angle ring for example rotates because it’s rolled for structural stability and not drilled to an ASME B16.5 pressure rating standard.

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

A lap joint flange consists of a loose ring and a stub end welded to the pipe, and is usually a two part fitting. The ring rotates freely over the pipe and stub end making bolt alignment easy and the ring is always un-wetted by the fluid. Compare this to the slip-on flange which is one piece, that slides over the pipe and needs to be welded - slip-ons are cheaper and simpler, but can only be removed by cutting the pipe and the entire flange comes into contact with the media. Where frequent disassembly is required and expensive alloys are needed, this type is a more economic option than a slip-on, which suits lower pressure, moderate service applications.

What is the difference between a lap joint flange and a van stone flange?

In steel piping nomenclature these are one and the same fitting - a loose ring turning on a flared edge of the stub-end and sometimes they are still referred to as a van stone - a name passed down from plastic/lined and duct piping where the stub end takes on a flared form. It’s all about bolt alignment and keeping the flange ring out of the stream, and it’s the same principle whether they’re called lap joint or van stone.

What is the difference between a Type A and a Type B stub end?

Their tabulated difference is the lap fillet radius, not length. A Type A stub end has a large corner radius to seat inside the bore of a lap joint flange; a Type B has a small radius to fit under a slip-on flange used as a backing ring. Use Type A with a true lap joint flange. Type C is the flared (van stone) form with lap thickness about 75% of the pipe wall.

When should I not use a lap joint flange?

Avoid lap joint flanges in cyclic or vibrating service. This assembly has low fatigue resistance, and it is the base metal of the stub end — not the weld — that fatigues over time. For severe or fluctuating loads, a butt-welded weld-neck flange is the correct choice. Lap joint flanges are at their best on steady-service lines that need frequent disassembly or alloy cost economy.

What materials are lap joint flanges and stub ends made of?

Backing rings are made from either carbon steel (ASTM A105 or A350 LF2 for low temp service) or stainless (A182 F304/F316/F316L) steel. The stub ends supplied are manufactured from matching or superior grade material (A234 WPB carbon; A403 WP304/316L stainless; or duplex and alloy for sour service or service with chlorides). As only the stub end comes in contact with the media, the common cost economy is to use a carbon steel backing ring with an alloy stub end.

Do you provide a material test certificate, and what is the lead time?

Every Synbase lap joint flange and stub end ships with an EN 10204 3.1 MTC and a stamped heat number; 3.2 third-party certification is available on request. Standard stock pairs typically ship in 1–2 weeks, while alloy or non-standard custom pairs run about 3–4 weeks — we confirm the exact lead time against your RFQ.