Steam pipe sizing
Enter the gauge pressure and steam flow to get a recommended pipe size by velocity or pressure-drop basis. All assumptions and sources are listed below.
Verification: comparison with published values
The same inputs are run through Spirax Sarco, TLV, and a Korean field example, and compared with this calculator. Pressure-loss figures can differ by a few percent due to the assumed roughness value.
| Item | Published value | Calculator value | Source |
|---|---|---|---|
| T4 | |||
| V (150A, 6,989 kg/h) | 25.000 m/s | 24.993 m/s | Spirax Sarco, Pipes and Pipe Sizing 표 10.2.4 (ASME Sch40 기준) |
| T5 | |||
| 필요 안지름 | 130.3 mm | 130.3 mm | Spirax Sarco, Pipes and Pipe Sizing 예제 10.2.4 |
| asme40 150A 유속 | 17.880 m/s | 17.880 m/s | Spirax Sarco, Pipes and Pipe Sizing 예제 10.2.4 |
| T6a | |||
| 유속 | 17.880 m/s | 17.880 m/s | TLV 계산기 (유속법), 2026-10-26 직접 실행 |
| 100 m 손실 (우리는 거칠기 0.046 mm 로 TLV 보다 약 2 % 낮음) | 0.0699 bar | 0.0685 bar | TLV 계산기 (유속법), 2026-10-26 직접 실행 |
| T6b | |||
| 유속 (150A) | 18.610 m/s | 18.610 m/s | TLV 계산기 (유속법), 2026-10-26 직접 실행 |
| 100 m 손실 | 0.0774 bar | 0.0758 bar | TLV 계산기 (유속법), 2026-10-26 직접 실행 |
| T6c | |||
| 유속 (65A) | 24.531 m/s | 24.531 m/s | TLV 계산기 (유속법), 2026-10-26 직접 실행 |
| 100 m 손실 | 0.2686 bar | 0.2625 bar | TLV 계산기 (유속법), 2026-10-26 직접 실행 |
| T6d | |||
| 유속 (100A) | 21.286 m/s | 21.286 m/s | TLV 계산기 (유속법), 2026-10-26 직접 실행 (90A 제외 확인) |
| 100 m 손실 | 0.1248 bar | 0.1221 bar | TLV 계산기 (유속법), 2026-10-26 직접 실행 (90A 제외 확인) |
| T6e | |||
| 유속 (40A, 1-1/2") | 23.308 m/s | 23.309 m/s | TLV 계산기 (유속법, IP 입력), 2026-10-26 직접 실행 |
| T6f | |||
| 유속 (80A, 3") | 43.006 m/s | 43.006 m/s | TLV 계산기 (압력손실법, IP 입력), 2026-10-26 직접 실행 |
| T7 | |||
| 필요 안지름 | 39.710 mm | 39.710 mm | Spirax Sarco 예제 10.2.2 (압력손실 기준), TLV [3] |
| stpg40 40A 유속 | 13.499 m/s | 13.499 m/s | Spirax Sarco 예제 10.2.2 (압력손실 기준), TLV [3] |
| stpg40 40A 165 m 손실 | 0.3312 bar | 0.3312 bar | Spirax Sarco 예제 10.2.2 (압력손실 기준), TLV [3] |
| T8 | |||
| 유속 (65A, 2-1/2", ASHRAE 「약 13,000 fpm」) | 13,000.0 ft/min | 13,072.0 ft/min | ASHRAE 1997 Fundamentals 증기 배관 예제 (Armstrong Steam Conservation Guidelines CG-25 재수록) |
| T9 | |||
| 필요 안지름 | 81.310 mm | 81.308 mm | 국내 실무 블로그 예제 (참고용, [10]) |
| stpg40 100A 유속 | 15.793 m/s | 15.793 m/s | 국내 실무 블로그 예제 (참고용, [10]) |
Calculation basis
Based on dry saturated steam (quality x = 1). Saturation properties come from interpolating the IAPWS-IF97 steam table, and velocity/pressure loss use the same Darcy-Weisbach + Colebrook equations as the duct and pipe calculators.
| Item | Equation | Note |
|---|---|---|
| Absolute pressure | p_abs = p_g + 101.325 kPa | Adds standard atmospheric pressure, 101.325 kPa |
| Saturation properties (table interpolation) | T_sat, v_f, v_g, h_f, h_g = f(p_abs) | 4-point Lagrange interpolation in ln(p) |
| Mass flow rate | ṁ = q, 또는 ṁ = 3600 · Q(kW) / h_fg | For heat power inputs (kW, MBH), divide by latent heat h_fg |
| Volumetric flow rate | Q = ṁ · v_g | Mass flow rate times specific volume v_g |
| Bore from velocity basis | D = √(4Q / (πV)) | Solved directly from the design velocity |
| Bore from pressure-loss basis | R(D) = R_target | R(D) = target solved by bisection in log D (same method as the pipe calculator) |
| Reynolds number and friction factor | 1/√f = −2 log₁₀( ε/(3.7D) + 2.51/(Re√f) ) | Colebrook equation (same solver as the duct and pipe calculators) |
Pipe size tables
Pick a pipe schedule to see the outside diameter, wall thickness, and bore for each size.
STPG Sch40 (KS D 3562 / JIS G3454)
KS D 3562 / JIS G 3454 carbon steel pipe for pressure service Sch40. Default in this calculator.
| Size | Outside dia. mm | Wall mm | Bore mm |
|---|---|---|---|
| 15A | 21.7 | 2.8 | 16.1 |
| 20A | 27.2 | 2.9 | 21.4 |
| 25A | 34.0 | 3.4 | 27.2 |
| 32A | 42.7 | 3.6 | 35.5 |
| 40A | 48.6 | 3.7 | 41.2 |
| 50A | 60.5 | 3.9 | 52.7 |
| 65A | 76.3 | 5.2 | 65.9 |
| 80A | 89.1 | 5.5 | 78.1 |
| 100A | 114.3 | 6.0 | 102.3 |
| 125A | 139.8 | 6.6 | 126.6 |
| 150A | 165.2 | 7.1 | 151.0 |
| 200A | 216.3 | 8.2 | 199.9 |
| 250A | 267.4 | 9.3 | 248.8 |
| 300A | 318.5 | 10.3 | 297.9 |
SGP (KS D 3507 / JIS G3452)
KS D 3507 / JIS G 3452 carbon steel pipe for ordinary piping (SPP/SGP). Only for use below 1 MPa (KDS 31 25 25:2021).
| Size | Outside dia. mm | Wall mm | Bore mm |
|---|---|---|---|
| 15A | 21.7 | 2.8 | 16.1 |
| 20A | 27.2 | 2.8 | 21.6 |
| 25A | 34.0 | 3.2 | 27.6 |
| 32A | 42.7 | 3.5 | 35.7 |
| 40A | 48.6 | 3.5 | 41.6 |
| 50A | 60.5 | 3.8 | 52.9 |
| 65A | 76.3 | 4.2 | 67.9 |
| 80A | 89.1 | 4.2 | 80.7 |
| 100A | 114.3 | 4.5 | 105.3 |
| 125A | 139.8 | 4.5 | 130.8 |
| 150A | 165.2 | 5.0 | 155.2 |
| 200A | 216.3 | 5.8 | 204.7 |
| 250A | 267.4 | 6.6 | 254.2 |
| 300A | 318.5 | 6.9 | 304.7 |
ASME B36.10M Sch40
ASME B36.10M Sch40 (inch sizes).
| Size | Outside dia. mm | Wall mm | Bore mm |
|---|---|---|---|
| 15A (1/2) | 21.34 | 2.77 | 15.8 |
| 20A (3/4) | 26.67 | 2.87 | 20.93 |
| 25A (1) | 33.4 | 3.38 | 26.65 |
| 32A (1-1/4) | 42.16 | 3.56 | 35.05 |
| 40A (1-1/2) | 48.26 | 3.68 | 40.89 |
| 50A (2) | 60.33 | 3.91 | 52.5 |
| 65A (2-1/2) | 73.03 | 5.16 | 62.71 |
| 80A (3) | 88.9 | 5.49 | 77.93 |
| 100A (4) | 114.3 | 6.02 | 102.26 |
| 125A (5) | 141.3 | 6.55 | 128.19 |
| 150A (6) | 168.28 | 7.11 | 154.05 |
| 200A (8) | 219.08 | 8.18 | 202.72 |
| 250A (10) | 273.05 | 9.27 | 254.51 |
| 300A (12) | 323.85 | 10.31 | 303.23 |
Pipe roughness ε
Material values from Moody's 1944 friction factor chart, converted to mm. Roughness grows with age and water quality, so enter other values with Custom.
| Material | ε (mm) | Moody's value |
|---|---|---|
| Commercial steel | 0.046 | 0.00015 ft |
| Galvanized steel | 0.15 | 0.0005 ft |
| Drawn tubing (copper, brass) | 0.0015 | 0.000005 ft |
Saturated steam table (IAPWS-IF97)
The exact table this calculator interpolates (computed with iapws 1.5.5, matching CoolProp IF97 to 15 digits).
| Pressure (abs.) kPa | Saturation temp. °C | Specific volume v_g m³/kg | Latent heat h_fg kJ/kg |
|---|---|---|---|
| 10.0 | 45.8 | 14.67 | 2,392.1 |
| 15.0 | 54.0 | 10.02 | 2,372.4 |
| 20.0 | 60.1 | 7.648 | 2,357.5 |
| 30.0 | 69.1 | 5.229 | 2,335.3 |
| 40.0 | 75.9 | 3.993 | 2,318.5 |
| 50.0 | 81.3 | 3.240 | 2,304.7 |
| 70.0 | 89.9 | 2.365 | 2,282.7 |
| 101 | 100.0 | 1.673 | 2,256.5 |
| 150 | 111.4 | 1.159 | 2,226.0 |
| 200 | 120.2 | 0.8857 | 2,201.6 |
| 250 | 127.4 | 0.7187 | 2,181.2 |
| 300 | 133.5 | 0.6058 | 2,163.4 |
| 400 | 143.6 | 0.4624 | 2,133.3 |
| 500 | 151.8 | 0.3748 | 2,107.9 |
| 600 | 158.8 | 0.3156 | 2,085.6 |
| 700 | 165.0 | 0.2728 | 2,065.6 |
| 800 | 170.4 | 0.2403 | 2,047.3 |
| 1,000 | 179.9 | 0.1943 | 2,014.4 |
| 1,200 | 188.0 | 0.1633 | 1,985.3 |
| 1,400 | 195.0 | 0.1408 | 1,958.8 |
| 1,600 | 201.4 | 0.1237 | 1,934.3 |
| 2,000 | 212.4 | 0.0996 | 1,889.8 |
| 2,500 | 224.0 | 0.0799 | 1,840.1 |
| 3,000 | 233.9 | 0.0667 | 1,794.9 |
| 3,500 | 242.6 | 0.0571 | 1,753.0 |
| 4,000 | 250.4 | 0.0498 | 1,713.5 |
| 4,500 | 257.4 | 0.0441 | 1,675.9 |
| 5,000 | 263.9 | 0.0394 | 1,639.7 |
Recommended velocity and pressure loss
25 m/s for saturated steam and 35 to 40 m/s for superheated steam are common practice per Spirax Sarco and TLV. For the pressure-loss basis, 0.1 to 0.2 bar per 100 m (10 to 20 kPa) is a typical range.
The practical limit is about 40 m/s; above that, noise and erosion risk increase. For runs longer than 50 m, it is good practice to re-check the pressure-loss basis even after sizing by velocity.
Per KDS 31 25 25:2021, total pressure loss should not exceed one-third of the initial gauge pressure. Per Crane TP-410, once the loss exceeds about 10% of the absolute pressure, the single-point (incompressible) Darcy-Weisbach assumption loses accuracy, so the run should be split and recalculated.
Sources
- Spirax Sarco, Steam Engineering Tutorials, "Pipes and Pipe Sizing"
- TLV, Steam Line Sizing Calculator
- ASHRAE Handbook, Fundamentals (SI), chapter "Steam Systems"
- Crane Co., Technical Paper No. 410, "Flow of Fluids"
- Ministry of Land, Infrastructure and Transport (Korea), KDS 31 25 25:2021 "Piping Systems"
- IAPWS-IF97 (International Association for the Properties of Water and Steam), computed with the iapws package (1.5.5)
Frequently asked questions
Can this calculator be used for wet or superheated steam?
No. This calculator assumes dry saturated steam only (quality x = 1). Wet steam has a smaller specific volume and superheated steam a larger one, so the required bore would differ.
Why do the results differ slightly from Spirax Sarco or TLV?
Small differences in the assumed pipe roughness, rounded pipe-table dimensions, and interpolation method can lead to a few percent difference in pressure loss. Values that do not depend on roughness, like velocity and required bore, usually match to several decimal places. See the verification table below for a direct comparison.
When should SGP (black pipe) not be used?
Per KDS 31 25 25:2021, SGP (SPP) may not be used once the design pressure reaches 1 MPa (10 kgf/cm², about 145 psi). Above that pressure, choose a pressure-piping schedule such as STPG.
Last updated 2026-10-26.