Valve Test Pressure Chart – API 598 Hydrostatic Test & ASME B16.34 P-T Rating
Complete reference for industrial valve test pressures. Covers API 598 hydrostatic body test, seat test, and pneumatic air test for ASME Class 150–2500. Includes ASME B16.34 maximum pressure vs temperature for WCB carbon steel, and PN flange test pressures per EN 12266. Published by Supreme Valves India.
Quick Summary
- API 598 defines hydrostatic shell (body) test at 1.5× rated pressure, seat test at 1.1× rated pressure, and pneumatic air test at 7 kg/cm² (100 psig)
- Class 150 body test = 30 kg/cm² (427 psig), seat test = 22 kg/cm² (313 psig)
- Class 300 body test = 78 kg/cm² (1109 psig), seat test = 57 kg/cm² (811 psig)
- Class 600 body test = 156 kg/cm² (2219 psig), seat test = 115 kg/cm² (1636 psig)
- ASME B16.34 WCB Class 150 at ambient = 20.0 kg/cm², drops to 5.6 kg/cm² at 425°C
- PN-16 body test = 24.0 kg/cm², seat test = 17.6 kg/cm² per EN 12266
API 598 – Testing Pressure (ASME Classes)
Hydrostatic body (shell) test, seat closure test, and pneumatic air test pressures for ASME pressure classes 150# through 2500#. All values in kg/cm² with psig equivalents.
| Class | Hydro Test | Air Test (Seat) |
|
|---|---|---|---|
| Body (Shell) | Seat | ||
| 150# | 30 kg/cm² (427 psig) | 22 kg/cm² (313 psig) | 7 kg/cm² (100 psig) |
| 300# | 78 kg/cm² (1109 psig) | 57 kg/cm² (811 psig) | 7 kg/cm² (100 psig) |
| 600# | 156 kg/cm² (2219 psig) | 115 kg/cm² (1636 psig) | 7 kg/cm² (100 psig) |
| 800# | 210 kg/cm² (2987 psig) | 154 kg/cm² (2190 psig) | 7 kg/cm² (100 psig) |
| 900# | 234 kg/cm² (3328 psig) | 172 kg/cm² (2446 psig) | 7 kg/cm² (100 psig) |
| 1500# | 390 kg/cm² (5547 psig) | 286 kg/cm² (4068 psig) | 7 kg/cm² (100 psig) |
| 2500# | 651 kg/cm² (9259 psig) | 477 kg/cm² (6785 psig) | 7 kg/cm² (100 psig) |
Note: Unit is kg/cm² (psig). Body test = 1.5× rated CWP. Seat test = 1.1× rated CWP. Air test is constant at 7 kg/cm² (100 psig) for all classes. Test medium: clean water for hydrostatic, dry air or nitrogen for pneumatic.
How to Read This Table: The body (shell) test verifies the pressure integrity of the valve body and bonnet — the valve is partially open and pressurized. The seat test verifies the sealing of the disc/ball against the seat — the valve is fully closed. The air test is a low-pressure pneumatic check for bubble-tight shutoff.
API 598 / EN 12266 – Hydraulic Test Pressure (PN Ratings)
Test pressures for PN-rated (metric) valves per API 598 and EN 12266. Covers PN-06 through PN-40.
| Standard | Body Test | Seat Test | Air Test |
|---|---|---|---|
| PN-06 | 09.0 kg/cm² | 06.6 kg/cm² | 7 kg/cm² |
| PN-10 | 15.0 kg/cm² | 11.0 kg/cm² | 7 kg/cm² |
| PN-16 | 24.0 kg/cm² | 17.6 kg/cm² | 7 kg/cm² |
| PN-25 | 37.5 kg/cm² | 27.5 kg/cm² | 7 kg/cm² |
| PN-40 | 60.0 kg/cm² | 44.0 kg/cm² | 7 kg/cm² |
Note: Unit is kg/cm². Body test = 1.5× PN rating. Seat test = 1.1× PN rating. Air test = 7 kg/cm² for all PN ratings. These values apply to steel, stainless steel, and alloy steel valves.
PN to ASME Class Equivalents: PN-10 ≈ Class 150 (low range), PN-16 ≈ Class 150, PN-25 ≈ Class 150–300, PN-40 ≈ Class 300. These are approximate — always verify with the applicable standard for your project.
ASME B16.34 – Max Pressure vs Temperature (WCB Carbon Steel)
Maximum allowable non-shock working pressure at elevated temperatures for WCB (ASTM A216 Gr. WCB) carbon steel valves. As temperature increases, allowable pressure decreases.
| Class | @ -29 to +38°C (Ambient) |
@ +200°C | @ +300°C | @ +350°C | @ +425°C |
|---|---|---|---|---|---|
| 150# | 20.0 | 14.0 | 10.4 | 8.5 | 5.6 |
| 300# | 52.1 | 44.6 | 40.6 | 38.3 | 23.2 |
| 600# | 104.1 | 89.3 | 81.1 | 76.6 | 58.6 |
| 800# | 138.8 | 119.1 | 108.3 | 102.1 | 78.2 |
| 900# | 156.2 | 134.0 | 121.8 | 114.9 | 88.0 |
| 1500# | 260.3 | 223.0 | 203.0 | 191.5 | 146.6 |
| 2500# | 433.8 | 372.0 | 338.3 | 319.0 | 244.4 |
Note: Unit is kg/cm². Material: ASTM A216 WCB (carbon steel casting) / ASTM A105 (carbon steel forging), ASME B16.34 Group 1.1. For temperatures above 425°C, use alloy steel (WC6/WC9). Maximum temperature limit for WCB = 538°C (1000°F).
Important: These are maximum allowable non-shock working pressures. For services with thermal cycling, vibration, or pressure surges, apply appropriate derating. For sour service (H₂S), material must also comply with NACE MR0175/ISO 15156. Always verify with the latest edition of ASME B16.34.
How Valve Testing Works
Step-by-Step Test Procedure
- Shell (Body) Test: Valve is partially open. Both ends are blanked off. Water is filled and pressurized to 1.5× CWP. Hold for required duration. Inspect for leakage through body, bonnet, and gland.
- Seat (Closure) Test: Valve is fully closed. Pressure is applied from one side at 1.1× CWP. Measure leakage past the seat on the downstream side. Compare against allowable leakage rate.
- Air (Pneumatic) Test: Valve is closed. Low-pressure air (7 kg/cm²) is applied. Downstream side is submerged in water or soap solution applied. Check for bubbles indicating seat leakage.
Test Duration per API 598
| Valve Size | Shell Test | Seat Test |
|---|---|---|
| ≤ DN50 (2") | 15 sec | 15 sec |
| DN65–DN150 (2½"–6") | 60 sec | 60 sec |
| DN200–DN300 (8"–12") | 120 sec | 120 sec |
| ≥ DN350 (14"+) | 300 sec | 300 sec |
Seat Leakage Classes (ANSI/FCI 70-2)
| Class | Leakage Rate | Typical Valve |
|---|---|---|
| II | 0.5% of rated Cv | Globe (single seat) |
| IV | 0.01% of rated Cv | Globe (balanced plug) |
| V | 5 × 10⁻⁴ ml/min/inch | Control valve (tight shutoff) |
| VI | Bubble-tight | Ball, butterfly (soft seat) |
Quick Conversion Reference
Pressure Units
- 1 kg/cm² = 14.2233 psig
- 1 bar = 14.5038 psig
- 1 kg/cm² = 0.9807 bar
- 1 MPa = 10.197 kg/cm²
- 1 atm = 1.0332 kg/cm²
Temperature
- °F = (°C × 9/5) + 32
- °C = (°F − 32) × 5/9
- 200°C = 392°F
- 300°C = 572°F
- 425°C = 797°F
Need more conversions? Use our interactive unit converter for pressure, temperature, Cv/Kv, and pipe size calculations.
Frequently Asked Questions
What is API 598 valve testing?
API 598 is the industry standard for valve inspection, examination, and testing. It specifies three types of factory acceptance tests: (1) Shell (body) hydrostatic test at 1.5× rated cold working pressure — tests the pressure integrity of the valve body and bonnet. (2) Seat closure hydrostatic test at 1.1× rated pressure — tests the sealing ability of the valve disc or ball against the seat. (3) Pneumatic (air) seat test at 7 kg/cm² (100 psig) — a low-pressure bubble test to verify seat tightness. Test duration depends on valve size, ranging from 15 seconds for small valves to 300 seconds for large valves.
What is the hydrostatic test pressure for a Class 150 valve?
Per API 598, the hydrostatic test pressures for a Class 150 valve are: Body (shell) test = 30 kg/cm² (427 psig), which is 1.5× the rated cold working pressure of 20 kg/cm². Seat test = 22 kg/cm² (313 psig), which is 1.1× the rated pressure. Air test = 7 kg/cm² (100 psig). These pressures apply at ambient temperature using clean water as the test medium.
What is the difference between body test and seat test?
Body (shell) test checks the pressure integrity of the valve body, bonnet, and all pressure-containing parts. The valve is partially open and pressurized to 1.5× rated pressure — no leakage is allowed through the body wall, bonnet joint, or gland. Seat test checks the sealing ability of the valve disc/ball against the seat. The valve is fully closed and pressure is applied from one side at 1.1× rated pressure. Allowable leakage depends on the valve type and the specified leakage class (ANSI/FCI 70-2).
What is the maximum pressure for a Class 150 WCB valve at 300°C?
Per ASME B16.34, the maximum allowable working pressure for a Class 150 valve in WCB (carbon steel, Group 1.1) at 300°C is 10.4 kg/cm² (approximately 148 psig). At ambient temperature (-29 to 38°C), the same valve is rated at 20.0 kg/cm² (285 psig). The pressure rating decreases as temperature increases because the yield strength and tensile strength of the material reduce at elevated temperatures.
What is the test pressure for PN-16 valves?
Per API 598 / EN 12266, the hydraulic test pressures for PN-16 valves are: Body test = 24.0 kg/cm² (1.5× PN rating), Seat test = 17.6 kg/cm² (1.1× PN rating), Air test = 7 kg/cm². PN-16 is approximately equivalent to ASME Class 150 for most applications. These values apply to steel, stainless steel, and alloy steel valves at ambient temperature.
How long should a valve hydrostatic test be held?
Per API 598, the minimum test hold duration depends on valve size: NPS ≤ 2" (DN50) = 15 seconds, NPS 2½"–6" (DN65–150) = 60 seconds, NPS 8"–12" (DN200–300) = 120 seconds, NPS ≥ 14" (DN350+) = 300 seconds (5 minutes). Some end-user specifications (e.g., Shell DEP, Saudi Aramco SAES, ADNOC) may require longer hold times, typically 2–5 minutes for all sizes.
What is ASME B16.34 pressure-temperature rating?
ASME B16.34 defines the maximum allowable non-shock working pressure for flanged, threaded, and welding-end valves at various temperatures. As temperature increases, the allowable pressure decreases because material strength reduces. The ratings are organized by material group (e.g., Group 1.1 for WCB carbon steel) and pressure class (150, 300, 600, 800, 900, 1500, 2500). For example, Class 300 WCB at ambient = 52.1 kg/cm², but at 425°C it drops to 23.2 kg/cm². For full P-T data across all materials, see our P-T Rating Calculator.
Related Technical Resources
P-T Rating Calculator
Interactive ASME B16.34 lookup for all materials and classes
Valve Sizing CalculatorCalculate Cv/Kv for liquid, gas, and steam service
Valve Standards ReferenceAPI 598, API 600, ASME B16.34, BS 6755 and more
Valve Material GuideWCB vs SS316 vs Duplex — temperature limits and corrosion
Need Valves with Test Certificates?
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