Valve Test Pressure Chart – API 598 Hydrostatic Test & ASME B16.34 P-T Rating

Q: What is API 598 valve testing?

API 598 is the standard for valve inspection, examination, and testing. It specifies three types of tests: (1) Shell (body) hydrostatic test – tests the pressure-containing boundary of the valve at 1.5× rated pressure using water. (2) Seat closure test – tests the sealing ability of the valve seat at 1.1× rated pressure. (3) Pneumatic (air) seat test – low-pressure air test at 7 kg/cm² (100 psig) to check for seat leakage using bubble method. Test duration depends on valve size: 15 seconds for valves ≤2", 60 seconds for 2.5"–6", 120 seconds for 8"–12", and 300 seconds for 14" and above.

Q: 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. 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 leakage class (ANSI/FCI 70-2).

Q: 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.

Q: How long should a valve hydrostatic test be held?

Per API 598, the minimum test duration for hydrostatic tests depends on valve size: NPS ≤2" (DN50) = 15 seconds, NPS 2.5"–6" (DN65–150) = 60 seconds, NPS 8"–12" (DN200–300) = 120 seconds, NPS ≥14" (DN350+) = 300 seconds. For shell (body) tests, the duration is the same. Some end-user specifications (e.g., Shell DEP, Aramco SAES) may require longer hold times.

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 pressure-temperature ratings for WCB, SS316 & LCC materials, expanded PN test pressures (PN-06 to PN-160) per EN 12266, API 598 allowable leakage rates, interactive pressure unit converter, and engineering FAQs. 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
Soft-seated valves = zero leakage required; metal-seated per API 598 Table 8/9

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 in parentheses.

Class	Rated CWP kg/cm² (psig)	Hydro Test		Air Test (Seat)	Test Factor
Class	Rated CWP kg/cm² (psig)	Body (Shell)	Seat	Air Test (Seat)	Test Factor
150#	20.0 (285)	30 kg/cm² (427)	22 kg/cm² (313)	7 (100)	1.5× / 1.1×
300#	52.1 (740)	78 kg/cm² (1,109)	57 kg/cm² (811)	7 (100)	1.5× / 1.1×
600#	104.1 (1,480)	156 kg/cm² (2,219)	115 kg/cm² (1,636)	7 (100)	1.5× / 1.1×
800#	140.6 (2,000)	210 kg/cm² (2,987)	154 kg/cm² (2,190)	7 (100)	1.5× / 1.1×
900#	156.2 (2,220)	234 kg/cm² (3,328)	172 kg/cm² (2,446)	7 (100)	1.5× / 1.1×
1500#	260.3 (3,705)	390 kg/cm² (5,547)	286 kg/cm² (4,068)	7 (100)	1.5× / 1.1×
2500#	433.8 (6,170)	651 kg/cm² (9,259)	477 kg/cm² (6,785)	7 (100)	1.5× / 1.1×

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. CWP = Cold Working Pressure at ambient temperature (-29 to 38°C).

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. The "Rated CWP" column shows the maximum cold working pressure per ASME B16.34 at ambient temperature.

API 598 / EN 12266 – Hydraulic Test Pressure (PN Ratings)

Test pressures for PN-rated (metric/DIN/EN) valves per API 598 and EN 12266-1. Expanded from PN-06 through PN-160. All values in kg/cm².

PN Rating	Body Test (1.5× PN)	Seat Test (1.1× PN)	Air Test	Approx. ASME Class Equiv.
PN-06	9.0 kg/cm²	6.6 kg/cm²	7 kg/cm²	—
PN-10	15.0 kg/cm²	11.0 kg/cm²	7 kg/cm²	Class 150 (low)
PN-16	24.0 kg/cm²	17.6 kg/cm²	7 kg/cm²	Class 150
PN-25	37.5 kg/cm²	27.5 kg/cm²	7 kg/cm²	Class 150–300
PN-40	60.0 kg/cm²	44.0 kg/cm²	7 kg/cm²	Class 300
PN-63	94.5 kg/cm²	69.3 kg/cm²	7 kg/cm²	Class 600 (low)
PN-100	150.0 kg/cm²	110.0 kg/cm²	7 kg/cm²	Class 600
PN-160	240.0 kg/cm²	176.0 kg/cm²	7 kg/cm²	Class 900

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. ASME Class equivalents are approximate — always verify with the applicable standard. PN-63 and above are common in European (DIN/EN) high-pressure applications.

PN to ASME Class Conversion: PN-10 ≈ Class 150 (low range), PN-16 ≈ Class 150, PN-25 ≈ Class 150–300, PN-40 ≈ Class 300, PN-63 ≈ Class 600 (low), PN-100 ≈ Class 600, PN-160 ≈ Class 900. These are approximate equivalents based on pressure ratings at ambient temperature — always verify with the project specification.

ASME B16.34 – Max Pressure vs Temperature

Maximum allowable non-shock working pressure (kg/cm²) at elevated temperatures. Select a material group to view the P-T rating table.

Material: ASTM A216 WCB (casting) / ASTM A105 (forging) — Carbon Steel. Max temp: 538°C (1000°F). ASME B16.34 Group 1.1.

Class	-29 to +38°C (Ambient)	+100°C	+200°C	+300°C	+350°C	+400°C	+425°C
150#	20.0	17.7	14.0	10.4	8.5	7.0	5.6
300#	52.1	50.1	44.6	40.6	38.3	33.3	23.2
600#	104.1	100.2	89.3	81.1	76.6	66.6	58.6
800#	138.8	133.6	119.1	108.3	102.1	88.8	78.2
900#	156.2	150.3	134.0	121.8	114.9	99.8	88.0
1500#	260.3	250.5	223.0	203.0	191.5	166.4	146.6
2500#	433.8	417.5	372.0	338.3	319.0	277.4	244.4

Note: Unit is kg/cm². For temperatures above 425°C, use alloy steel (WC6/WC9). Max temp limit for WCB = 538°C (1000°F).

Material: ASTM A351 CF8M (casting) / ASTM A182 F316 (forging) — Austenitic Stainless Steel. Max temp: 816°C (1500°F). ASME B16.34 Group 2.2.

Class	-29 to +38°C (Ambient)	+100°C	+200°C	+300°C	+400°C	+500°C	+538°C
150#	20.0	17.2	14.0	12.0	10.5	9.5	9.2
300#	52.1	44.8	36.4	31.3	27.3	24.7	24.0
600#	104.1	89.6	72.8	62.6	54.6	49.5	48.0
800#	138.8	119.5	97.1	83.5	72.8	66.0	64.0
900#	156.2	134.4	109.2	93.9	81.9	74.2	72.0
1500#	260.3	224.0	182.0	156.5	136.5	123.7	120.0
2500#	433.8	373.3	303.3	260.8	227.5	206.2	200.0

Note: SS316 retains significantly more strength at elevated temperatures vs WCB. At 425°C, SS316 Cl.150 ≈ 10.2 kg/cm² vs WCB 5.6 kg/cm². Max operating temp = 816°C (1500°F).

Material: ASTM A352 LCC (casting) / ASTM A350 LF2 (forging) — Low-Temperature Carbon Steel. Min temp: -46°C (-50°F). Max temp: 340°C (650°F). ASME B16.34 Group 1.2.

Class	-46 to +38°C (Ambient)	+100°C	+150°C	+200°C	+250°C	+300°C	+340°C
150#	20.0	18.3	16.9	15.5	13.8	11.5	9.8
300#	52.1	47.7	44.0	40.3	35.9	30.0	25.5
600#	104.1	95.4	88.0	80.6	71.8	60.0	51.0
900#	156.2	143.1	132.0	120.9	107.7	90.0	76.5
1500#	260.3	238.5	220.0	201.5	179.5	150.0	127.5
2500#	433.8	397.5	366.7	335.8	299.2	250.0	212.5

Note: LCC/LF2 is designed for low-temperature service (cryogenic). Impact tested to -46°C. Same ambient ratings as WCB but max temperature limited to 340°C (650°F). For temperatures below -46°C, use LCB (-59°C) or austenitic SS.

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.

Test Pressure Comparison Chart

Visual comparison of body test, seat test, and air test pressures across ASME pressure classes.

Interactive Pressure Unit Converter

Convert between common pressure units used in valve testing. Enter a value in any unit and see all conversions instantly.

Pressure Converter

Enter Value

Unit

kg/cm²

30.00

psi (psig)

426.70

bar

29.42

kPa

2,942.1

MPa

2.942

atm

29.04

Pressure Unit Relationships

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 Conversions

°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 full interactive unit converter for pressure, temperature, Cv/Kv, and pipe size calculations.

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)

API 598 – Allowable Seat Leakage Rates

Maximum allowable seat leakage during closure (seat) test per API 598. Rates differ based on valve type (resilient-seated vs metal-seated) and valve size.

Resilient (Soft) Seated Valves

Valve Size	Liquid Test	Gas Test
All sizes	Zero leakage	Zero leakage

Applies to: Ball valves (PTFE/RPTFE seat), butterfly valves (EPDM/NBR seat), plug valves with soft inserts. Zero visible leakage is required for both liquid and gas closure tests.

Metal Seated Valves – Liquid Test

NPS (DN)	Allowable Rate (drops/min)	ml/min
≤ 2" (DN50)	0	0
2½"–3" (DN65–80)	2	0.10
4" (DN100)	3	0.15
6" (DN150)	4	0.20
8" (DN200)	6	0.30
10" (DN250)	8	0.40
12" (DN300)	12	0.60
14"–16" (DN350–400)	14	0.70
18"–20" (DN450–500)	18	0.90
24" (DN600)	24	1.20

Applies to: Gate valves, globe valves, check valves, and metal-seated ball/butterfly valves. Per API 598 Table 8 (9th edition). 1 drop ≈ 0.05 ml.

Metal Seated Valves – Gas (Pneumatic) Test

NPS (DN)	Gate Valve (bubbles/min)	Globe Valve (bubbles/min)	Check Valve (bubbles/min)
≤ 2" (DN50)	0	0	Note 1
2½"–4" (DN65–100)	8	8	Note 1
6" (DN150)	12	12	Note 1
8" (DN200)	20	20	Note 1
10"–12" (DN250–300)	24	24	Note 1
14"–16" (DN350–400)	28	28	Note 1
18"+ (DN450+)	36	36	Note 1

Note 1: Check valves are typically not gas-tested per API 598. If required by the purchaser, leakage rates per the gate valve column apply. Bubble count measured at downstream using water immersion method. Per API 598 Table 9.

ANSI/FCI 70-2 Leakage Classes vs API 598: API 598 defines factory acceptance test leakage limits. ANSI/FCI 70-2 defines operational leakage classes (II, III, IV, V, VI) used in control valve specifications. Class VI (bubble-tight) is equivalent to API 598 "zero leakage" for soft-seated valves. For critical shutoff applications, always specify the leakage class in addition to API 598.

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 Calculator

Calculate Cv/Kv for liquid, gas, and steam service

Valve Standards Reference

API 598, API 600, ASME B16.34, BS 6755 and more

Valve Material Guide

WCB vs SS316 vs Duplex — temperature limits and corrosion

Need Valves with Test Certificates?

Supreme Valves India supplies valves with API 598 hydrostatic test certificates, EN 10204 3.1 material certificates, and IBR Form III-C. Complete documentation for every valve.

Request Quote with Test Certs WhatsApp