TECTULby IMR

Fluid conduction · Pipe fittings

TECHNICAL DATA SHEET

FT-TC-ACC-NIP-001

Issue date: July 22, 2026 · Rev. 001

Check the current version

SKU VT-niple-acero-carbon-sch40-1 (carbon steel nipple sch 40/80/160, made to measure) · family of 6 references: black, galvanized sch 40 and STD, stainless, galvanized barrel and stainless barrel · made-to-measure nipples are quoted by size and length

1. Pipe nipple dimensions by schedule (ASTM A733)

A nipple is manufactured by cutting and threading pipe of the ordered schedule: its dimensions are those of ASME B36.10 pipe plus the lengths standardized by ASTM A733. The close length is the shortest threadable length of each size: two NPT threads that almost touch, with no plain body between them (A733, para. 4.2, allows fewer imperfect threads on close nipples than B1.20.1).

Master table per size, NPS 1/8″–4″

Close lengths and availability per length per ASTM A733, Table 2, concordant with the Anvil/ASC SPF manufacturer submittal (2022): in 1/2″ increments up to 6″ and 1″ increments from 6″ to 12″; the standard also tabulates lengths up to 24″ and allows special lengths (para. 4.3.2). Note A to A733 Table 2: nipples shorter than close are not recommended for pressure service. ASTM A733 covers NPS 1/8″–12″ and also schedule 160 and XXS (Table 1); the TECTUL catalog fabricates sch 40, sch 80 and sch 160 to measure.

Canonical NPT thread table per size (ASME B1.20.1)

Taper NPT thread with 1:16 taper on diameter and 60° flank angle (ASME B1.20.1). L2 is the effective thread length of the male end — the one that works when sealing; L4 the overall threaded length including incomplete threads; h = 0.8 × pitch is the nominal depth of the truncated thread. This is the canonical thread table of the TECTUL catalog: the threaded-pipe data sheets (e.g. FT-TC-TUB-GALV-001) point here instead of repeating it.

General specifications

2. Engineering calculations: the nipple is pipe — minus the thread

The nipple has no rating of its own: it inherits the allowable pressure of the pipe it is cut from — the Barlow calculation of data sheets FT-TC-TUB-SCH40-001 and FT-TC-TUB-SCH80-001 (P = 2·S·E·t_ef/D with S = 137.9 MPa at ≤38 °C per ASME B31.3-2024, Table A-1, for seamless A53/A106 Gr B; E = 1.00; t_ef = 0.875·nominal t for the −12.5% tolerance). But the thread cut must be subtracted from that wall: ASME B31.3-2024, para. 304.1.1, requires the minimum thickness t_m = t + c to include in c the nominal thread depth (dimension h of ASME B1.20.1). On a nipple, threaded at both ends, the governing section is the one left under the thread.

Worked example — 1/2″ nipple: schedule 40 vs schedule 80

1. Common data: D = 21.3 mm; 1/2″ NPT thread, 14 TPI → h = 0.8 × 1.814 = 1.45 mm (canonical table in section 1).
2. Sch 40: nominal t 2.77 mm → t_ef = 0.875 × 2.77 = 2.424 mm. Wall remaining under the thread: 2.424 − 1.451 = 0.973 mm. P = 2 × 137.9 × 1.00 × 0.973 / 21.3 = 12.59 MPa ≈ 125 bar (1,827 psi) — against 313 bar for the same pipe at full wall: the thread removes 60% of the capacity.
3. Sch 80: nominal t 3.73 mm → t_ef = 3.264 mm. Under the thread: 3.264 − 1.451 = 1.813 mm. P = 2 × 137.9 × 1.813 / 21.3 = 23.47 MPa ≈ 234 bar (3,404 psi) — 87% more than the threaded sch 40 nipple.

The arithmetic explains what intuition misses: at 1/2″ the NPT thread cuts 1.45 mm out of a 2.77 mm nominal sch 40 wall — it eats more than half the wall. That is why the same size in sch 80 (3.73 mm wall) keeps almost twice the steel under the thread, and why the code itself makes it a requirement: ASME B31.3-2024, Table 314.2.1, requires minimum schedule 80 for externally threaded carbon steel components NPS ≤ 1-1/2 in normal fluid service (gas, steam, hydrocarbons; the exception is Category D service — full detail in FT-TC-TUB-SCH80-001). Specifying sch 80 nipples for gas or steam is not an inspector's whim: it is the wall that remains after threading.

Allowable pressure calculated under the thread, per size (≤38 °C)

Declared method: Barlow on the guaranteed minimum wall (0.875·t) minus the nominal thread depth h of B1.20.1 — the c deduction criterion of ASME B31.3-2024, para. 304.1.1 — with no corrosion allowance, rounded down. The unthreaded-pipe columns reproduce (or derive with the same declared method) the values of FT-TC-TUB-SCH40-001 and FT-TC-TUB-SCH80-001, where the full series with temperature derating S(T) is published. For A312 stainless nipples the geometry of the deduction is identical; the allowable stress S of each grade is in FT-TC-TUB-INOX-001. These calculated values are not a certified lot rating — read the technical notice.

Two design takeaways: (1) in a threaded line the weak link is almost never the fitting (class 150 malleable allows 300 psi; class 3000 forged is rated as sch 160 pipe) but the nipple, because it is the thinnest pipe in the system and it is threaded; (2) the h deduction is geometric and fixed per size, so it penalizes thin walls proportionally more — the underlying reason threaded schedule 40 loses 50% to 60% of its capacity while schedule 80 loses 40% to 45%.

3. Standard nipple, close nipple and barrel nipple

ASTM A733 (Fig. 1) distinguishes three nipple geometries; the TECTUL catalog fabricates or supplies all three:

Close nipple: what it is for — and when not to use it

A close nipple has no plain body: every gripping surface is thread. Tightening it with a direct pipe wrench damages the very thread that must seal afterwards; correct assembly uses an internal nipple wrench, which grips the bore, or the fitting is turned rather than the nipple. Practical consequences of its geometry:

• Once a fitting-close-fitting assembly is made up, it cannot be adjusted by tightening the nipple: only by turning the fittings — plan the make-up sequence.
• The nipple's whole length has thread-reduced wall (section 2 quantifies the deduction): on demanding lines specify it in sch 80.
• A733, Table 2, note A: nipples even shorter than close are not recommended for pressure service.
• The close nipple's thread has fewer imperfect threads than a regular NPT thread (A733, para. 4.2): it is a factory-made part, not a pipe field-threaded twice until the threads "almost touch".

The Colombian gas installation code (NTC 2505, fourth update) contains no restriction specific to close nipples; its requirements applicable to every threaded nipple are those of the installation section: taper NPT thread, approved sealants and corrosion protection of exposed thread (see installation note).

4. TECTUL made-to-measure fabrication and finishes

TECTUL manufactures nipples — it does not merely resell them. The nipple is cut and threaded in-shop from certified pipe (A53/A106/API 5L black, galvanized A53, stainless A312), which enables what a closed catalog cannot:

• Made-to-measure length: any length between close and the full 6 m random length, not just the A733 standard series; the standard provides for it as special lengths (para. 4.3.2) with the same tolerance (±1.6 mm up to 12″ long, ±3.2 mm above; para. 4.3.3).
• Schedule on demand: sch 40, sch 80 and sch 160 in black (sch 160 and XXS are covered by A733, Table 1, from 1/2″ up); sch 40 and STD in galvanized; sch 40 and sch 80 in 304/316 stainless.
• Gaged threads: NPT verified with a ring gage per the A733 gaging procedure (para. 5.3: hand-tight ring, rap and re-tighten, pipe end flush with the gage face ±1 turn).
• Traceability: the nipple inherits the heat certificate (MTC) of the parent pipe; supplied upon request (A733, para. 7).

Finishes and thread protection

On the galvanized nipple the parent pipe is hot-dip coated inside and outside, but the thread is cut after galvanizing: the thread flanks and the cut ends are bare steel (A733, para. 4.5). This is the product's normal behavior, not a defect — and it demands touch-up after assembly: zinc-rich paint per ASTM A780/A780M-20 on every exposed thread, the same as for threaded galvanized pipe (full procedure in FT-TC-TUB-GALV-001). On black nipples protection is that of the system (coating or non-corrosive service); on A312 stainless the passive film restores itself and needs no touch-up.

5. Frequently asked questions

What is a close nipple?

It is the shortest threadable nipple of its size — at 1/2″ it measures 1-1/8″ (28.6 mm) — formed by two NPT threads that almost touch, with no plain body between them (ASTM A733, Table 2). It joins two female connections at the shortest possible distance; since it has no gripping surface, it is assembled by turning the fittings or with an internal nipple wrench, never by biting the threads with a pipe wrench.

Schedule 40 vs schedule 80 nipple: how much pressure does each take?

At 1/2″ and ≤38 °C: 125 bar (1,827 psi) calculated under the thread for sch 40 and 234 bar (3,404 psi) for sch 80 — 87% more. The difference is not that of plain pipe (313 vs 422 bar): the NPT thread cuts h = 1.45 mm from both, and that fixed deduction punishes the thin sch 40 wall (0.973 mm left) far more than the sch 80 wall (1.813 mm left). The full table per size is in section 2.

Why do gas and steam lines require schedule 80 nipples?

Because ASME B31.3-2024, Table 314.2.1, requires minimum schedule 80 for externally threaded carbon steel components NPS ≤ 1-1/2 in normal fluid service: when schedule 40 is threaded, the thread consumes more than half the wall (h = 1.45 mm out of a 2.77 mm nominal wall at 1/2″). Category D service (non-flammable, non-toxic fluid, ≤150 psi and ≤186 °C) is the exception that allows threaded schedule 40.

Does a galvanized nipple have zinc on the thread?

No: per ASTM A733 (para. 4.5) the nipple is made from pipe hot-dip galvanized inside and outside, but the threads are cut afterwards and are bare steel, as are the cut ends. After assembly, any exposed thread is touched up with zinc-rich paint per ASTM A780/A780M-20 (≥65% zinc in dry film, ≥50 µm).

What does the Colombian gas code require for installing threaded nipples?

NTC 2505 (fourth update) requires taper NPT-type threads (clause 5.2.1.1a, via NTC 332), anaerobic sealants per NTC 2635 or PTFE tape per BS 7786 / MIL SPEC T-27730-A — it forbids hemp and paints (clause 4.8) —, corrosion protection of the exposed thread portion (5.2.1.1c), and it allows no threaded joints on pipe larger than 100.8 mm / 4″ (5.2.1.1d) nor threaded connections on buried metallic pipe (5.1.1.1).

6. Application notes

7. Technical notice and limitation of liability