Weld Connector Tube Fittings: Tube Socket Weld & Male Pipe Weld Connectors
A weld connector is an instrumentation compression tube fitting that grips and seals on the tube's outside diameter using one or two ferrules on one end. The other end terminates in a weld end, a tube socket weld, male pipe weld, or butt weld, so a gaugeable instrument line can be permanently joined to a welded pipe or tube run. Crestflo makes these in 316/316L, duplex, and nickel alloys up to 2″ (50 mm) tube OD. They come in single- or double-ferrule versions, get tested to ASTM F1387, and are dimensionally engineered as drop-in replacements for the major brands.
On this page, a weld connector means one specific thing: a stainless-steel or alloy instrumentation fluid-system fitting with a weld end connection. It's not an electrical weld connector. Not a welding-cable lug, either. And it's not a structural weld coupling.
Weld Connector Tube Fitting: Also Known As
The same part is called by several names on drawings, catalogs, and RFQs. Buyers specify it as a tube weld connector, a weld connector fitting, a welded tube connector, or a tube-to-weld connector, and, with the words reversed, a tube fitting weld connector, as well as an instrumentation weld connector, a weld end connector, or a weld-end tube fitting. Split by the weld-end style, it is the tube socket weld connector (also written as a tube socket weld adapter), the male pipe weld connector or male pipe weld tube fitting (abbreviated MPW connector), the pipe socket weld connector, or the butt weld connector; the socketed pattern is sometimes labeled a tube weld gland or simply a weld gland. Every one of these describes the weld-connector family covered here; the weld-end styles below split it by the joint it welds into.
What Is a Weld Connector Tube Fitting? (Tube-to-Weld Working Principle)
A weld connector caps off an instrument tube run and hands the job over to a welded joint. On one end, the ferrule swages onto the tube OD, forming a leak-tight compression seal that also grips the tube so it can't pull out. The other end is a machined weld prep, fused to the mating pipe or tube by socket weld or butt weld. Specifiers reach for this fitting when the transition has to be permanent and high-integrity. A welded joint has no thread to back off and no seal to age, so it's the pick where a threaded or purely gaugeable joint won't cut it: high-temperature service, welded hook-ups, lines built to a welding code. Since the weld side is all-metal fusion, the connector adds no elastomer and no extra leak path to the run it welds into.
Weld End Styles: Tube Socket Weld, Male Pipe Weld (MPW), Pipe Socket Weld & Butt Weld
The weld-connector family comes down to one defining feature: a weld end opposite the ferrule tube end. Each style ships as a standard item, or gets made to order, in whatever alloy and size your line requires.
| Weld end style | Description | Mating joint | Governing standard | Best for |
|---|---|---|---|---|
| Tube socket weld | Tube seats into a machined socket bore, fillet-welded at the shoulder | Instrument tube | Socket-weld end dims per ASME B16.11 | Tube-to-tube welded instrument lines |
| Male pipe weld (MPW) | Male weld spigot that socket-welds into a pipe fitting or coupling | Pipe / pipe socket | ASME B31.3 welded joint | Tube line into a welded pipe run |
| Pipe socket weld | Female socket bore sized to a pipe end | Pipe | ASME B16.11 | Tube to a socket-welded pipe branch |
| Butt weld | Weld-prepped end aligned and full-penetration butt-welded | Tube or pipe | ASME B31.3 | High-integrity, full-bore welded joints |
Choosing between a tube socket weld and a butt weld comes down to what kind of joint you actually need. A tube socket weld seats the mating tube inside a machined socket, then fillet-welds the shoulder, which gives you fast, repeatable fit-up. A butt weld aligns the tube ends and produces a full-penetration, full-bore joint with no internal crevice. When cleanliness, flow, or fatigue life matters most, that's the one to pick.
For the dedicated end-type category pages, see socket weld tube fittings and butt weld tube fittings. If you need automatic, high-purity welded connections, check orbital weld fittings.
Weld-end socket bore and land dimensions follow the applicable ASME standard, and they can be customized to your requirement. Request the dimensional detail for your size and schedule from our engineering team.
Weld Connector Design & Ferrule Technology: Single vs Double Ferrule
Crestflo weld connectors come in two tube-side designs: double-ferrule (two-ferrule) and single-ferrule. The two-ferrule geometry keeps sealing and gripping as separate jobs, so the seal holds up under vibration, pressure cycling, and thermal movement. The single-ferrule design, by contrast, is simpler and uses fewer parts, making it a good fit for suited services. Ferrules come hardened or non-hardened depending on what's needed, and every part carries a heat/lot number. Take a look at the single-ferrule design and the matching nut-and-ferrule sets. For the trade-offs, our single vs double ferrule and hardened vs non-hardened ferrules guides lay them out.
Weld Connector Materials: 316/316L Stainless, Duplex & Nickel Alloys
316/316L stainless is the standard for general instrumentation work. When the media turns corrosive, sour, high-temperature, or heavy with chloride, the full alloy ladder is there. Grades ship to ASTM A269 / A276 / A479, with values set per the applicable standard, and they're adjustable to what the job needs. Because the joint is welded, the connector body, the weld end, and the mating pipe or tube must use alloys compatible for welding: a matched grade, or a qualified filler. Our engineering team checks that against your weld procedure.
| Alloy family | Grades offered | Selection driver | Material page |
|---|---|---|---|
| Austenitic stainless | 304/304L, 316/316L, 904L | General to elevated-chloride service | 316/316L, 304/304L |
| Duplex / super-austenitic | Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20 | Chloride stress-cracking, strength | Duplex 2205, Super Duplex 2507 |
| Nickel alloys | Inconel 600/601/625/718/825, Incoloy 800/800H/825, Monel 400/K500, Hastelloy C-276/C-22/B-2/B-3/X, Nickel 200/201 | Sour, acidic, cryogenic, high-temp | Inconel 625, Monel 400, Hastelloy C-276 |
| Titanium | Titanium Gr2 | Seawater, chloride, weight | Titanium Gr2 |
Unsure which grade the job calls for? Start with our material selection by service guide, or try the alloy selector instead.
Weld Connector Sizes: 1/8″ to 2″ OD, Imperial and Metric
Tube-side connections span tube OD from 1/8″ to 2″ (50 mm). Fractional sizes include 1/8″, 1/4″, 3/8″, 1/2″, 3/4″, and 1″, each with a metric equivalent, and the more common ones get their own landing pages. Weld-end bore and schedule match the mating pipe or tube per the applicable ASME standard, confirmed at the time of order.
| Imperial OD | Metric OD | Size page |
|---|---|---|
| 1/8″ | 3 mm equiv. | 1/8-inch fittings |
| 1/4″ | 6 mm equiv. | 1/4-inch fittings |
| 3/8″ | 10 mm equiv. | 3/8-inch fittings |
| 1/2″ | 12 mm equiv. | 1/2-inch fittings |
| 3/4″ | 19 mm equiv. | 3/4-inch fittings |
| 1″ | 25 mm equiv. | 1-inch fittings |
| — | 6 / 8 / 10 / 12 mm | 6mm, 8mm, 10mm, 12mm |
We offer both metric and imperial/fractional weld connectors. For sizing details, check the full tube fitting size chart or the tube OD reference.
High-Pressure Weld Connector Ratings: Pressure, Temperature & Standards Conformance
A weld connector doesn't carry one blanket pressure number. On the tube side, working pressure follows the tube OD, wall thickness, and alloy, worked out on the allowable-stress basis of ASME B31.3. On the weld side, the joint itself sets the limit, along with the mating pipe or tube schedule and the alloy in use. Values come from the applicable standard and can be customized to the requirement at hand.
The compression tube-fitting family is qualified to ASTM F1387.
Because the weld joint is all-metal, with no elastomer anywhere in it, service temperature is bounded by the chosen alloy rather than by a soft seal. Check each alloy's material page for its temperature envelope.
A high-pressure weld connector is only as strong as the weakest point in that chain. A heavier tube wall and a higher-strength alloy will push the ceiling up, but that number has to come down as temperature climbs, following the alloy's allowable-stress curve. There's no single high-pressure figure that holds across every service condition.
Size the tube side with our tube-pressure calculator, then check the limits against the pressure-temperature derating guide.
| Attribute | Specification |
|---|---|
| Configuration | Straight weld connector; tube socket weld, male pipe weld (MPW), pipe socket weld, butt weld ends |
| Tube-side sealing | Single or double (two) ferrule compression on tube OD |
| Ferrules | Hardened or non-hardened to requirement |
| Size range | Tube OD 1/8″–2″ (50 mm); imperial and metric |
| Weld-end dimensions | Socket-weld ends per ASME B16.11; welded joints per ASME B31.3 |
| Material standards | ASTM A269 / A276 / A479 |
| Performance qualification | Tested per ASTM F1387; NACE MR0175 / ISO 15156 compliant on request |
| Traceability | Heat/lot number on every part; EN 10204 MTC 3.1 standard, 3.2 on request |
| Finishes | Material finish, electropolish, passivation, silver anti-galling plating; oxygen-clean on request |
Swagelok & Parker Weld Connector Interchange, Backed by ASTM F1387
Crestflo weld connectors are built as dimensional drop-in equivalents for Swagelok, Parker, Hoke, Hy-Lok, and Fitok weld connectors. No guesswork. That interchange isn't a look-alike claim; it's backed by ASTM F1387 performance qualification. We present it as engineered equivalence, never as a compatibility or intermix statement. Instead of posting a static part-number table, we build the mapping for your bill of materials directly: request your Swagelok® or Parker® cross-reference, and our engineering team sends back the matched Crestflo equivalents. Start at the Swagelok cross-reference, the Parker A-Lok cross-reference, or the interchange lookup. Swagelok® and Parker® are trademarks of their respective owners.
Weld Connector Certifications, Testing & Traceability
Crestflo is ISO 9001 / 14001 / 45001 & PED certified. Its weld connectors are qualified to ASTM F1387, and NACE MR0175 / ISO 15156 compliance is available for sour service. Every part carries a heat/lot number and ships standard with an EN 10204 MTC 3.1 certificate; 3.2 is available on request. The compression tube-fitting family goes through a full test regime: hydraulic proof, burst and impulse, pneumatic, flexure fatigue, rotary flex, vibration, thermal cycling, pull-out, and vacuum. Positive material identification (PMI) and NDT are handled in-house, while destructive testing takes place at ISO/IEC 17025-accredited laboratories. Third-party inspection can be arranged on request. See material traceability, our testing & inspection capability, and the ASTM F1387 and NACE MR0175 standard pages.
Why Buy Weld Connector Tube Fittings From Crestflo
Crestflo is the instrumentation division of an export house that's been in business for four decades, recognized by the Government of India, with a proven track record delivering into the Middle East. That kind of supply discipline sits behind a brand focused squarely on instrumentation. For weld connectors, here's what it means:
- ASTM F1387-qualified drop-in interchange for Swagelok, Parker, Hoke, Hy-Lok, and Fitok. Most competitors won't publish that kind of interchange proof.
- Ready stock for standard items, made-to-order for specials, 6–8 week delivery. Compare that to the 20+ weeks common from the majors.
- Every weld-end style (tube socket weld, male pipe weld, pipe socket weld, and butt weld) comes in both imperial and metric, with single or double ferrule options.
- Full alloy range, from 316/316L through duplex, 254 SMO, Inconel, Hastelloy, and Titanium Gr2. That's a deeper lineup than you'll find on SS-only distributor listings.
- ISO 9001 / 14001 / 45001 & PED certified, with EN 10204 MTC 3.1 (3.2 on request) and a heat/lot number stamped on every part.
- Indian origin, though US and European melt is available on request, with full material traceability. TAA and domestic-melt options are there when your specification calls for them.
Datasheets and CAD models are available to customers on request. For more background, see the Crestflo Engineering Team page, our stance on US-origin & compliance, and our lead time page.
Request a Weld Connector Quote or Sample
Give us the weld-end style, the tube size, the mating pipe or tube schedule, and the alloy. We'll match the part and confirm delivery. Request a quote, request a free sample, take a look at the private-label program, or become a distributor. Reach Crestflo's US team at sales@crestflousa.com, +1 346 594 9005, Houston, TX.
Weld connectors handle welded instrument hook-ups and tube-to-pipe transitions. They're used across oil and gas, offshore, petrochemical, hydrogen, LNG & cryogenic, steam tracing, and analytical sampling systems.
Weld Connector Tube Fitting FAQ
What is a weld connector tube fitting?
A weld connector is an instrumentation compression tube fitting that seals against the tube OD using one or two ferrules on one end. On the other end it carries a weld termination, tube socket weld, male pipe weld, or butt weld. This permanently joins a gaugeable instrument line to a welded pipe or tube joint.
What weld end styles are available?
Four end types are available: tube socket weld, male pipe weld (MPW), pipe socket weld, and butt weld. Socket-weld ends are sized to ASME B16.11. Welded joints, meanwhile, follow ASME B31.3. For details, check the weld-end style table, plus our socket weld and butt weld pages.
What sizes do Crestflo weld connectors come in?
Tube-side connections span 1/8″ through 2″ OD (50 mm), available in imperial/fractional sizing as well as metric. The weld-end bore and schedule are matched to whatever pipe or tube they mate with.
Which alloys can I order?
The material range covers 304/304L, 316/316L, and 904L, along with Duplex 2205 and Super Duplex 2507. It also includes 254 SMO, AL-6XN, and Alloy 20. Nickel alloys are part of the range as well: Inconel, Incoloy, Monel, and Hastelloy, plus Nickel 200/201. Titanium Gr2 rounds out the list. Weld ends and mating components are supplied in weldable-compatible grades throughout.
What pressure rating does a weld connector have?
There's no single blanket number here. The tube side tracks the tube OD, wall thickness, and alloy, worked out from the allowable-stress basis in ASME B31.3. Weld side is different: joint, mating schedule, and alloy set the value there. The compression tube-fitting family carries qualification to ASTM F1387. Values follow the applicable standard, and they can be adjusted to requirement.
Are single and double ferrule weld connectors available?
Yes. Weld connectors come in both single-ferrule and double-ferrule designs on the tube side. Ferrules are supplied hardened or non-hardened, depending on what the job calls for.
How is a weld connector welded and installed?
Swage the ferrule end onto the instrument tube first, then join the weld end to the mating pipe or tube. A tube socket weld connector seats the mating tube in its socket bore and gets fillet-welded at the shoulder. A male pipe weld end socket-welds into a pipe fitting or coupling. A butt weld end is aligned and full-penetration welded. Weld to a qualified weld procedure (WPS) per ASME B31.3, and make sure the weld end and mating component are in weldable-compatible alloys, matched grade, or a qualified filler.
Are Crestflo weld connectors interchangeable with Swagelok or Parker?
They're built as dimensional drop-in equivalents, qualified to ASTM F1387. Send us your Swagelok® or Parker® cross-reference, and our engineering team will match it to the right Crestflo part numbers.
Are they NACE compliant, and where are they made?
Weld connectors can be supplied to meet NACE MR0175 / ISO 15156 for sour service applications. They're of Indian origin, though US or European melt is available on request. Full material traceability comes standard, backed by EN 10204 MTC 3.1, with 3.2 available on request.
Related Weld Connector Resources
- Connector family: connector tube fitting · male connector · female connector · port connector
- Weld ends come in three flavors: socket weld tube fittings · butt weld tube fittings · orbital weld fittings
- Governing standards include NACE MR0175, ASME B16.11, ASME B31.3, ASTM F1387 and ASTM A269: ASME B16.11 · ASME B31.3 · ASTM F1387 · ASTM A269 · NACE MR0175
- Pillar: tube fittings