Hot-dip galvanized conveyance pipe, heavy type (SCH 40)

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Carbon-steel pipe with schedule 40 wall, hot-dip galvanized with a minimum of 550 g/m² of zinc on each surface (ASTM A53), for conveying cold water, compressed air and non-corrosive gases in NPT-threaded lines. 6 m lengths, 12 sizes from 1/4″ to 6″. Dimensions per ASME B36.10-2022. Not suitable for steam or water above 60 °C (section 3).

VT-86944 · heavy-type SCH 40 galvanized pipe, threadable · 6 m lengths · price from $148,034 COP + VAT per length (Jul 2026, confirmed on quotation)

1. Technical specifications

Dimensions and calculated working pressure by size

NPS	DN	Outside Ø		SCH 40 wall		Weight (black pipe)		Allowable pressure at ≤38 °C¹
		mm	in	mm	in	kg/m	lb/ft	bar	psi
1/4″	8	13.7	0.540	2.24	0.088	0.63	0.42	335	4,864
3/8″	10	17.1	0.675	2.31	0.091	0.84	0.56	277	4,019
1/2″	15	21.3	0.840	2.77	0.109	1.27	0.85	266	3,869
3/4″	20	26.7	1.050	2.87	0.113	1.69	1.14	220	3,197
1″	25	33.4	1.315	3.38	0.133	2.50	1.68	207	3,010
1-1/4″	32	42.2	1.660	3.56	0.140	3.39	2.28	173	2,509
1-1/2″	40	48.3	1.900	3.68	0.145	4.05	2.72	156	2,266
2″	50	60.3	2.375	3.91	0.154	5.44	3.66	133	1,929
2-1/2″	65	73.0	2.875	5.16	0.203	8.63	5.80	144	2,102
3″	80	88.9	3.500	5.49	0.216	11.29	7.59	126	1,837
4″	100	114.3	4.500	6.02	0.237	16.07	10.80	108	1,566
6″	150	168.3	6.625	7.11	0.280	28.26	18.99	86	1,256

¹ Internal pressure calculated in section 2 (Barlow, S = 137.9 MPa, E = 0.85 for ERW manufacture, −12.5% wall tolerance), rounded down. It is not a certified rating for any lot: read the calculation basis and the technical notice. Weight is that of plain-end black pipe per ASME B36.10-2022; zinc adds the mass calculated in section 3.

General specifications

Product	Hot-dip galvanized carbon-steel pipe, schedule 40 wall (SCH 40) — the "heavy type" of the Colombian conveyance market
Material and grade	Carbon steel per ASTM A53. The calculations in this sheet use Gr B (yield ≥240 MPa / 35 ksi; tensile ≥415 MPa / 60 ksi); the certified grade of each lot appears in its mill test certificate (MTC) and is confirmed on quotation.
Manufacture	Electric-resistance-welded longitudinal seam, ERW (A53 Type E) — quality factor E = 0.85 per ASME B31.3-2024, Table A-1B. A seamless lot (Type S) carries E = 1.00, raising allowable pressure by 17.6%; manufacture type is confirmed on quotation.
Coating	Hot-dip zinc, minimum mass 550 g/m² (1.8 oz/ft²) on each surface — inside and outside — per ASTM A53/A53M-24, verifiable by ASTM A90/A90M testing (section 3)
Commercial class	"Heavy type" = schedule 40 wall (this sheet). The "light type" conveyance pipe is a thin-wall water pipe for medium and low pressure (certified in Colombia under NTC 5890) and has its own product page in the catalog.
Ends	NPT threaded (ASME B1.20.1) with plastic protector, or plain; confirmed on quotation (section 4)
Commercial length	6 m lengths
Wall tolerance	Minimum wall at any point ≥ 87.5% of nominal (−12.5%), per ASTM A53/A53M-24
Applicable standards	ASTM A53/A53M-24 (black and galvanized pipe) · NTC 3470:2021, Colombian equivalent of A53 · ASME B36.10-2022 (dimensions) · ASME B1.20.1 (NPT threads) · ASTM A90/A90M-21 (coating mass) · reference design code: ASME B31.3-2024

2. Engineering calculations (allowable internal pressure)

Allowable internal pressure is estimated with the Barlow formula, applying the wall manufacturing tolerance and the weld-quality factor. Every value used is declared below — nothing is silently assumed:

P = 2 · S · E · t_ef / D

S — basic allowable stress	S = 137.9 MPa (20.0 ksi) at ≤38 °C per ASME B31.3-2024, Table A-1, for ASTM A53 Gr B. If the lot certifies Gr A, S drops to 110.3 MPa (16.0 ksi) and the pressures in this sheet scale down accordingly.
E — quality factor	E = 0.85 for ERW welded pipe (A53 Type E) per ASME B31.3-2024, Table A-1B — the usual supply of galvanized conveyance pipe. This is why a welded pipe takes less pressure than the same seamless pipe: with E = 1.00 (Type S) the values rise 17.6% (at NPS 2″: 156 bar, the table in data sheet FT-TC-TUB-SCH40-001).
t_ef — effective wall	t_ef = 0.875 · t_nominal: the A53 manufacturing tolerance allows the wall to be up to 12.5% under nominal at any point, so the calculation uses the guaranteed minimum wall. Zinc thickness is not added: the coating protects, it does not carry pressure. No corrosion allowance is subtracted here (see Design, application notes).
D — outside diameter	Nominal outside diameter per ASME B36.10-2022 (table in section 1).

Worked example — NPS 2″ (DN 50)

1. Nominal SCH 40 wall: t = 3.91 mm; outside Ø: D = 60.3 mm (ASME B36.10-2022).
2. Effective wall: t_ef = 0.875 × 3.91 = 3.421 mm.
3. P = 2 × 137.9 MPa × 0.85 × 3.421 / 60.3 = 13.30 MPa ≈ 133 bar ≈ 1,929 psi.

Derived allowable pressure by size (≤38 °C, E = 0.85)

NPS	Effective wall	P (MPa)	P (bar)	P (psi)
1/4″	1.960 mm	33.54	335	4,864
3/8″	2.021 mm	27.71	277	4,019
1/2″	2.424 mm	26.68	266	3,869
3/4″	2.511 mm	22.05	220	3,197
1″	2.958 mm	20.76	207	3,010
1-1/4″	3.115 mm	17.30	173	2,509
1-1/2″	3.220 mm	15.63	156	2,266
2″	3.421 mm	13.30	133	1,929
2-1/2″	4.515 mm	14.50	144	2,102
3″	4.804 mm	12.67	126	1,837
4″	5.268 mm	10.80	108	1,566
6″	6.221 mm	8.67	86	1,256

Temperature derating — S(T) per ASME B31.3-2024, Table A-1

The allowable stress of A53 Gr B steel barely drops within the galvanized service range; the ceiling is set by the zinc coating, not the steel:

Temperature	S		Factor vs. 38 °C	Galvanized service?
	MPa	ksi
≤38 °C · 100 °F	137.9	20.0	1.000	Yes
93 °C · 200 °F	137.9	20.0	1.000	Dry fluids only (in water >60 °C zinc reverses its potential — section 3)
149 °C · 300 °F	137.9	20.0	1.000	Dry fluids only, up to 200 °C
204 °C · 400 °F	137.2	19.9	0.995	No — exceeds the coating's 200 °C limit

Above 200 °C of continuous exposure the outer free-zinc layer peels from the zinc-iron alloy layers (American Galvanizers Association). For higher-temperature service specify black pipe: data sheet FT-TC-TUB-SCH40-001.

3. Zinc coating: mass, service life and limits

Hot-dip galvanizing protects steel in two ways: as a barrier — zinc exposed to the atmosphere passivates into a basic zinc carbonate patina that slows its own corrosion — and as a sacrificial anode — zinc is anodic to steel in the galvanic series, so at cuts, scratches and edges it corrodes before the substrate does (American Galvanizers Association).

Minimum zinc mass	550 g/m² (1.8 oz/ft²) on each surface, inside and outside, per ASTM A53/A53M-24.
Equivalent thickness	≈77 µm per surface: 550 g/m² ÷ 7.14 g/cm³ (zinc density, CRC Handbook) = 77.0 µm. Real coatings usually exceed the minimum; each lot's value appears in its test report.
Measurement	ASTM A90/A90M-21: the reference gravimetric method of A53 — the coating of a specimen is stripped and the mass difference weighed.
Zinc melting point	419.5 °C (CRC Handbook); the useful service limit of the coating is far lower: 200 °C (see below).

Minimum zinc mass per meter of pipe (calculated)

With the A53 minimum mass per surface and B36.10 dimensions, zinc mass per meter is m = 0.550 kg/m² × π × (D_out + D_in):

NPS	Inside Ø	Min. zinc mass	Vs. black-pipe weight
1/4″	9.22 mm	0.040 kg/m	+6.3%
3/8″	12.48 mm	0.051 kg/m	+6.1%
1/2″	15.76 mm	0.064 kg/m	+5.0%
3/4″	20.96 mm	0.082 kg/m	+4.9%
1″	26.64 mm	0.104 kg/m	+4.1%
1-1/4″	35.08 mm	0.134 kg/m	+3.9%
1-1/2″	40.94 mm	0.154 kg/m	+3.8%
2″	52.48 mm	0.195 kg/m	+3.6%
2-1/2″	62.68 mm	0.234 kg/m	+2.7%
3″	77.92 mm	0.288 kg/m	+2.6%
4″	102.26 mm	0.374 kg/m	+2.3%
6″	154.08 mm	0.557 kg/m	+2.0%

Coating service life by atmospheric environment (ISO 9223)

Quotient estimate: life ≈ minimum thickness (77 µm) ÷ first-year zinc corrosion rate per corrosivity category (ISO 9223:2012, Table 2). It is a linear, conservative projection: the zinc rate decays after the first year as the patina consolidates (American Galvanizers Association).

ISO 9223 category	Typical environment	Zinc rate, 1st year	Estimated life of minimum coating (77 µm)
C2 (low)	Dry rural, minimal pollution (SO₂ < 5 µg/m³)	0.1–0.7 µm/yr	over 110 years
C3 (medium)	Urban with medium pollution (SO₂ 5–30 µg/m³) or coastal 1–30 km from the sea	0.7–2.1 µm/yr	36 to 110 years
C4 (high)	Industrial, or coastal under 1 km from the sea	2.1–4.2 µm/yr	18 to 36 years
C5 (very high)	Heavily polluted industrial; jetties and offshore structures	4.2–8.4 µm/yr	9 to 18 years
CX (extreme)	Marine splash zone; extreme industrial	8.4–25 µm/yr	3 to 9 years

Coating life is the time until zinc is locally exhausted on the outside surface exposed to the atmosphere (maintenance criterion: ~5% red rust). The inside surface is governed by the fluid's chemistry — hardness, oxygen, temperature — not by this table.

Temperature limits — and why not in steam or hot water

200 °C of continuous exposure is the maximum recommended by the American Galvanizers Association: above it, diffusion between the outer free-zinc layer and the zinc-iron alloy layers creates voids that peel the coating off; between 200 and 250 °C the alloy layers still protect, but peeling accelerates and continued exposure worsens it.

In water between 60 and 82 °C containing dissolved oxygen and bicarbonates, potential reversal occurs: zinc passivates, becomes cathodic to the steel and stops protecting it — attack then concentrates as pitting of the exposed steel (American Galvanizers Association). That is why galvanized pipe is not specified for steam, condensate return or hot water: a steam line also exceeds the coating's thermal limit. For those services use black pipe (data sheet FT-TC-TUB-SCH40-001).

4. NPT threading, touch-up and installation

Galvanized conveyance pipe is joined by threading, not welding: the arc burns the coating in the heat-affected zone — leaving bare steel exactly where corrosion concentrates most — and releases zinc oxide fumes (metal fume fever). If a joint does require welding, the area must be restored per ASTM A780/A780M-20.

NPT thread per ASME B1.20.1

Sizes	Threads per inch	Pitch
1/4″ and 3/8″	18	1.411 mm
1/2″ and 3/4″	14	1.814 mm
1″ to 2″	11½	2.209 mm
2-1/2″ to 6″	8	3.175 mm

Taper thread, 1:16 on diameter (3/4 in per foot), 60° flank angle (ASME B1.20.1). Threading cuts into the wall: the pressure in section 2 is at full wall — check the remaining wall under the thread on demanding lines. The schedule 40 wall is what makes the "heavy type" threadable.

Touch-up of exposed thread and damaged areas (cold galvanizing)

The cut thread is left uncoated. After assembly, touch up every exposed flight per ASTM A780/A780M-20 with zinc-rich paint: metallic zinc content in the dry film of 65–69% or above 92%, minimum thickness 50 µm (2 mils), over a clean, dry surface. For larger repairs, A780 also allows zinc thermal spraying or hot-applied zinc-alloy stick.

Galvanic couple: do not connect galvanized pipe directly to copper or brass: in the galvanic series zinc sacrifices itself at an accelerated rate against those metals. Insert dielectric unions and avoid water flowing from copper toward the galvanized run.

5. Application notes

6. Technical notice and limitation of liability