RPN® · Rolled-thread steel pipe nipples

Patented leak-tight pipe nipples that resist rust ~35× longer

Our threads are cold-formed, not cut. Rolling keeps the galvanized layer intact right across the sealing threads — so there's no bare steel, no field oiling, and no early rust where cut nipples corrode first. NPT (ASME B1.20.1) and BSPT (ISO 7), DN15–DN150.

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Patented Patent certificate available on request →
  • DN15–DN150
  • SCH 40 / 80
  • Galvanized or black
  • Test reports on request
RPN rolled-thread steel pipe nipples in black and galvanized finishes on a dark studio background

Traditional cut pipe thread VS Patented rolled thread

A drop-in swap for your current nipples — same fit, no hot work, no line change. Rust holds off about 35× longer in salt-spray, threads pull 31–60% stronger than cut in tests, and each joint stays leak-tight under a 5 MPa (~725 psi) pressure test — so fewer leaks, fewer rust-outs, and fewer customer callbacks.

✕Standard cut thread

Cross-section comparison: the rolled thread keeps a thicker wall while the cut thread is thinner at the thread
Thread & wallThinner at the thread. Cutting strips steel and zinc right where the joint seals.
Cut-thread pipe nipple heavily red-rusted at the thread after neutral salt-spray testing ✕
CorrosionFirst rust in about 6 h. Bare steel at the thread corrodes fast in salt-spray.
Diagram: seating a cut-thread joint takes 3 to 4 tool turns and usually a wrench ✕
Install3–4 turns to seat. Hand-tight, then 3–4 more turns — often with a wrench.

✓RPN rolled external thread

Galvanized rolled-thread steel pipe nipples with the zinc coating intact ✓
Thread & wallFull wall kept. Rolled, not cut — the wall and zinc stay intact.
Rolled galvanized pipe nipple with no red rust on the thread after neutral salt-spray testing ✓
Corrosion~35× longer to rust. Holds off red rust far longer in salt-spray.*
Diagram: seating a rolled-thread joint takes only 1.5 to 2 tool turns with standardized torque and less force ✓
Install1.5–2 turns to seat. Hand-tight plus 1.5–2 turns — torque-standardized, less force.

*Salt-spray tests (Shanghai Baoye, reports 10D051YW / 11D007YW): 175–259 h to first red rust vs ~5–6 h for cut-thread; samples still rust eventually. Sealing verified by 5 MPa hydraulic test (GB/T 241). Figures apply to rolled external thread. Full reports on request.

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The process

Formed by pressure, not cut.

Rolling shapes the thread by cold pressure instead of cutting it away.

  1. Full wall, full zinc goes in

    A galvanized steel pipe goes in with its full wall thickness and its complete zinc coating still on it.

  2. Hardened dies press the thread

    Hardened dies roll the thread into the pipe under cold pressure — no heat, no cutting tool removing material.

  3. The metal flows and hardens

    The metal flows into the thread shape and work-hardens as it forms. Nothing is cut away.

  4. It comes out intact

    The finished thread comes out with its wall thickness and zinc coating still intact.

Hand holding two pipe nipples after about six months side by side: the cut-thread nipple is rusted at the threads while the rolled-thread nipple is still intact
Field sample, ~6 months side by side: the cut-thread nipple (left) rusts first right at the threads — the rolled-thread nipple (right) is still intact.

Because it is cold-formed and chip-free, rolling keeps the wall and the hot-dip galvanized layer that cut threading strips away — which is why it tends to hold up better in the corrosion and strength tests shown elsewhere on this page.

Test evidence

Every claim has a report behind it.

Independent labs, real conditions, figures you can check. Below are four sample-level results under stated standards — corrosion, strength, sealing and structure. All numbers stay tied to the conditions that produced them.

01 · Corrosion — salt spray

Rolled thread holds the zinc far longer

Rolled and cut-thread pipe nipple samples racked side by side inside the neutral salt-spray chamber
Neutral salt spray comparison experiment — samples racked in the chamber (CTI)

Rolled galvanized samples reached first red rust at 175–259 h in earlier tests and 88–102 h in a later run — against roughly 5–6 h for the cut-thread control.

≈35× longer to first red rust than cut-thread, sample-level
  • Shanghai Baoye 10D051YW / 11D007YW: 175–259 h
  • CTI neutral salt spray, GB/T 10125-2021, run to 102 h
  • Samples still develop red rust eventually — not rust-proof.

02 · Strength — tensile

Higher max tensile force in the pulls tested

Diagram: tensile test with a rolled-thread nipple joint pulled to failure between machine grips
Max tensile force comparison experiment (diagram)

Across the test groups, rolled samples reached a higher maximum tensile force than the cut-thread samples before failure.

+31–60% in the DN15 test group; DN25 showed about +6%
  • Result range is per test group, not a general figure
  • Rolled thread displaces metal rather than cutting it away
  • Figures are sample-level and depend on size and batch.

03 · Sealing — hydraulic

Leak-tight thread fit under pressure

Diagram: hydraulic pressure test with the sealed rolled-thread joint holding 5 MPa on the gauge, PTFE tape applied
Hydraulic pressure test, PTFE tape applied (diagram)

On the pressure bench the joint showed no leakage at 5 MPa held for 5 seconds — a leak-tight thread fit under standard conditions.

5 MPa held 5 s with no leakage (GB/T 241)
  • Test standard: GB/T 241 hydraulic pressure
  • Test sample was sealed with PTFE thread tape
  • Tape stays a sensible extra insurance, not something we tell you to skip.

04 · Structure — metallurgy & X-ray

Cold-formed grain, zinc intact, no weld defects found

Micrograph of the rolled thread profile at 50x magnification from the third-party metallographic report
Metallography — rolled thread profile, 50× (report 2012F00023JX)

Metallography shows a cold-formed grain flow. Radiographic inspection found no weld-defect indications on the tested samples, and copper-sulfate dips confirm the coating held.

3 vs 1 rolled zinc stays intact at 3 dips; cut thread exposes base metal at 1
  • Metallographic: cold-formed grain, chip-free thread
  • Radiographic: no weld-defect indications on samples tested
  • Findings apply to the specific samples inspected.

Full reports available on request.See the salt-spray, tensile, pressure and metallurgy documents behind these figures before you commit.

Request test reports

Method comparison

Choosing a connection approach

Typical method considerations — not results from a head-to-head test. Final selection depends on applicable codes, medium, pressure, mating components, installation procedure and service environment.

Criterion Cut thread Welding Press-fit RPN rolled thread
Pressure-test and joint-sealing considerations Joint sealing depends on thread geometry and condition, the specified sealant, and correct assembly. Joint integrity depends on the qualified welding procedure, workmanship and inspection. Joint sealing depends on pipe preparation, an approved seal element and fitting, and completion of the specified press cycle. Tested samples: no leakage observed at 5 MPa for 5 s in hydraulic testing conducted to GB/T 241. This is not a gas-tightness guarantee; installed-joint performance also depends on mating threads, sealant and assembly.
Corrosion-protection considerations Cutting may remove local coating and expose steel at the thread; performance depends on subsequent protection and the service environment. On coated pipe, heat can disrupt protection around the joint; the specified post-weld protection system must be applied. No hot work at the joint; corrosion performance depends on pipe and fitting compatibility, exposed pipe ends and the service environment. In tested metallographic cross-sections, the zinc layer remained visible at the formed thread; see report 2012F00023JX. Field corrosion life still depends on coating condition and exposure.
Field connection workflow A pre-threaded nipple uses conventional threaded assembly with the specified sealant. Field-cut pipe additionally requires threading, deburring and cleaning. Requires hot-work controls, a qualified operator and the specified inspection procedure. No hot work; requires a compatible fitting, jaw/tool, pipe preparation and press cycle. Installs as a conventional threaded nipple using the specified sealant and assembly procedure; no welding or press tool is required for the nipple connection.
Serviceability Generally removable when accessible; thread condition or seizure may limit reassembly. Modification normally requires cutting out the joint and qualified rewelding. Not normally intended for disassembly; modification generally requires cutting out and replacing the connection. Threaded connection can be disassembled for service. Inspect the component and apply new approved sealant before any permitted reassembly; follow project, code and manufacturer requirements.
Process-footprint considerations Thread cutting removes material as metal chips and may use cutting fluid. Hot work uses energy and consumables and may require fume controls and post-weld coating repair. No hot work at the joint; uses a compatible fitting with a seal element and dedicated manual or powered tooling. Thread formation removes no material as thread-cutting chips, and field assembly requires no hot work. No overall carbon or ESG advantage is claimed without a comparative lifecycle assessment.

Send us your current specification — we'll confirm fit.

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Applications

Built for joints where a clean seal matters.

RPN rolled external-thread nipples fit tight and install without hot work, so they suit projects where a leak-tight thread fit, corrosion resistance, and fewer return trips matter. Here is where buyers put them to work.

Black steel natural-gas distribution pipes feeding multiple boilers in a mechanical room
01

Gas distribution

A leak-tight thread fit and a make-up of just 1.5–2 turns give crews a clean, repeatable joint on gas lines — with no welding permit needed on site.

Red commercial fire-sprinkler pipework installed above a ceiling service zone
02

Fire protection

Sprinkler and standpipe runs go together faster with no hot work, and the preserved galvanized layer helps the threads resist corrosion over time.

HVAC installer assembling galvanized metal pipework in a commercial building
03

HVAC and plumbing

Chilled-water, condensate, and supply lines benefit from a snug thread seal that passes a 5 MPa hydraulic pressure test (GB/T 241, on tested samples), plus quick chip-free assembly in tight spaces.

Pipe thread-rolling machine used for cold-forming external threads
04

Industrial and process piping

Threads formed cold instead of cut keep more of the protective coating intact, which helps hold up in demanding plant and process environments.

Black and galvanized threaded steel pipe nipple product range
05

Distributors and OEM

Private-label and resale ready in DN15–DN150, galvanized or black, NPT / BSP / BSPT — a consistent rolled product that means fewer callbacks by design for your customers.

Corrosion resistance, sealing, and strength figures are sample-level third-party results under stated test conditions. Rolled samples still develop red rust eventually and are not rust-proof.

Specifications

Sizes and specifications.

A quick reference for the rolled external thread nipple range. Need a size or thread not listed? Send your spec and we'll confirm the equivalent.

Rolled external thread nipple

Ext. thread only
Size range
DN15–DN150  (NPS 1/2"–6")
Thread
NPT / BSP / BSPT
Wall / schedule
SCH 40 / 80
Finish
Hot-dip galvanized or black
Thread type
Rolled external thread
Material
Low-carbon steel
Standards
NPT gauged to ASME B1.20.1; BSPT to ISO 7 — conformance on request
Galvanized rolled-thread pipe nipples and long pipes laid out across the size range
Size range shown end to end, from 1/4" up to 4".

Match your current part.

Send your current cut-thread spec and we'll match the equivalent rolled external part.

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Figures above apply to the rolled external thread product only.

FAQ

Questions engineers ask.

Straight answers on sealing, strength, corrosion and paperwork — with the test conditions kept attached, not stripped off.

01Do I still need sealing tape?

The rolled external thread forms a tight metal-to-metal fit and passes a 5 MPa hydraulic pressure test (GB/T 241). Many installers still add PTFE tape as extra insurance, and we'd suggest keeping it in your routine.

Note: the seal-test sample was made up with PTFE tape. Tape is optional extra insurance, not a guarantee it can be skipped.

02Does it come in internal thread?

Currently external thread only. The rolling process is applied to the outside thread of the nipple. Available across DN15–DN150 (NPS 1/2"–6"), SCH 40/80, galvanized or black, in NPT, BSP or BSPT.

03How much stronger is it?

In tensile testing the rolled thread carried a higher maximum tensile force than the cut-thread control. The gain depends on size — about +31–60% in the DN15 test group and +6% for DN25 — so it is not a single across-the-board number.

Sample-level results under stated test conditions; your figures will vary by size and batch.

04Will it rust?

It resists rust far longer than cut-thread. In neutral salt spray, rolled galvanized samples reached first red rust at 88–102 h (CTI, GB/T 10125-2021) and 175–259 h in earlier reports, versus ~6 h for the cut-thread control — roughly 35× longer.

Honest caveat: galvanized steel still corrodes eventually. These samples do develop red rust in the end — this is not a rust-proof product.

05What standards and reports do you have?

Threads are rolled to NPT, BSP or BSPT. Salt-spray, tensile, hydraulic, metallographic and radiographic reports are available on request, along with conformance statements and certificates.

Stamped third-party test report covers: salt spray, tensile, metallographic, radiographic and hydraulic
Third-party report package supplied on request.
06Can I get a sample?

Yes. Request a free sample — send us your size, thread type and quantity, and we'll match it to the right nipple and get it moving.

Still have a question about your line? Send us the spec — we'll answer straight.

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Get started

Get a free sample or a quote.

Tell us the sizes you run. We'll send a rolled external-thread sample to inspect and a quote for your exact spec - no obligation.

What you'll get back

  • A free sample A physical rolled external-thread nipple to check the thread fit and the galvanized finish by hand.
  • A quote for your sizes Priced for the DN sizes, schedule, and finish you actually use - DN15-DN150, SCH 40/80, galvanized or black.
  • The test reports Third-party salt-spray, hydraulic-pressure, and tensile results under their stated conditions - so you can judge the data yourself.

No pressure and no account needed - a real person reads every request and replies with the sample and the numbers.

Scope: rolled external thread only · NPT / BSP / BSPT

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