What is ASME B16.34 pressure-temperature rating?

ASME B16.34 defines the maximum allowable working pressure (MAWP) for valves at various temperatures. As temperature increases, the allowable pressure decreases because material strength reduces at elevated temperatures. The ratings are organized by material group (e.g., Group 1.1 for carbon steel WCB, Group 2.2 for SS316) and pressure class (150, 300, 600, 900, 1500, 2500).

What is the pressure rating of Class 150 at 100°F?

For Group 1.1 (carbon steel WCB/A105), Class 150 at 100°F (38°C): maximum allowable pressure = 285 psig (19.6 bar). For Group 2.1 (SS304/CF8), Class 150 at 100°F: 275 psig (19.0 bar). For Group 2.2 (SS316/CF8M), Class 150 at 100°F: 275 psig (19.0 bar). These are non-shock, static pressure ratings per ASME B16.34 Table 2.

What is the difference between Class 150 and PN20?

Class 150 (ASME) and PN20 (EN/ISO) are approximately equivalent but not identical. Class 150 at ambient temperature = 285 psig (19.6 bar) for carbon steel. PN20 = 20 bar at ambient. The key difference: ASME ratings vary with temperature per material group, while PN ratings are fixed at 20°C. At elevated temperatures, ASME provides specific derating curves. For practical purposes, Class 150 ≈ PN20, Class 300 ≈ PN50, Class 600 ≈ PN100.

At what temperature does carbon steel WCB lose its pressure rating?

Carbon steel (ASTM A216 WCB, Group 1.1) has a maximum temperature limit of 1000°F (538°C) per ASME B16.34. However, the pressure rating decreases significantly: Class 150 drops from 285 psig at 100°F to 170 psig at 600°F to 20 psig at 1000°F. For temperatures above 800°F, alloy steels (WC6, WC9) are recommended as they maintain higher strength at elevated temperatures.

ASME B16.34 Pressure-Temperature Rating Charts

Look up the maximum allowable working pressure for any valve at a given temperature. Select material group and pressure class to see the full P-T curve, or use the calculator for a specific temperature.

P-T Rating Calculator

Material Group

Pressure Class

Temperature

°F (enter -20 to 1000)

or Temperature (°C)

Auto-converts to °F

Pressure Rating Result

Material–

Pressure Class–

Temperature–

Max Allowable Pressure–

Group 1.1 – Carbon Steel (WCB / A105) – Pressure Ratings (psig)

Temp °F	Temp °C	CL 150	CL 300	CL 600	CL 900	CL 1500	CL 2500
-20 to 100	-29 to 38	285	740	1480	2220	3705	6170
200	93	260	675	1350	2025	3375	5625
300	149	230	655	1315	1970	3280	5470
400	204	200	635	1270	1900	3170	5280
500	260	170	600	1200	1795	2995	4990
600	316	140	550	1095	1640	2735	4560
650	343	125	535	1075	1610	2685	4475
700	371	110	505	1010	1510	2520	4200
750	399	95	410	825	1235	2060	3430
800	427	80	270	535	805	1340	2230
850	454	65	170	345	515	860	1430
900	482	50	105	205	310	515	860
950	510	35	50	105	155	260	430
1000	538	20	20	20	20	20	20

Group 2.2 – SS 316 (CF8M / F316) – Pressure Ratings (psig)

Temp °F	Temp °C	CL 150	CL 300	CL 600	CL 900	CL 1500	CL 2500
-20 to 100	-29 to 38	275	720	1440	2160	3600	6000
200	93	240	620	1245	1865	3110	5180
300	149	215	560	1120	1680	2800	4665
400	204	195	515	1025	1540	2565	4275
500	260	175	480	960	1440	2400	4000
600	316	160	450	900	1350	2250	3750
650	343	155	440	880	1320	2200	3665
700	371	150	430	855	1285	2140	3570
750	399	145	415	830	1245	2075	3460
800	427	140	395	790	1185	1975	3290
850	454	130	365	730	1095	1825	3040
900	482	120	335	665	1000	1665	2775
950	510	105	300	600	900	1500	2500
1000	538	90	265	530	795	1325	2205
1100	593	60	170	340	510	850	1415
1200	649	35	95	185	280	465	775
1500	816	20	20	20	20	20	20

Pressure Class Equivalents (ASME vs PN vs JIS)

ASME Class	PN (EN/ISO)	JIS (Japan)	Approx. bar @ 38°C	Approx. psig @ 100°F
150	PN 20	10K / 16K	19.6	285
300	PN 50	20K / 30K	51.0	740
600	PN 100	40K / 63K	102.0	1480
900	PN 150	–	153.0	2220
1500	PN 250	–	255.5	3705
2500	PN 420	–	425.4	6170

Note: ASME and PN ratings are NOT directly interchangeable. ASME ratings vary with temperature per material group. PN ratings are defined at 20°C. The equivalents above are approximate at ambient temperature for carbon steel. Always verify with the applicable standard.

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