Group 1.9 Pressure-Temperature Ratings

1.25Cr-0.5Mo alloy steel. The lightest of the common chrome-moly grades, used where carbon steel has lost too much of its rating but the service does not justify 2.25Cr-1Mo.

Standard: ASME B16.5
Group: Group 1.9
Materials: A182 F11 Cl. 2, A217 WC6, A387 Gr. 11 Cl. 2
Class 150 at 100 °F: 290 psig (20.0 bar)
Class 150 at 600 °F: 140 psig (9.7 bar)

ASME B16.5 pressure-temperature ratings for Group 1.9 materials, in psig.
Class	100 °F	200 °F	300 °F	400 °F	500 °F	600 °F	650 °F	700 °F	750 °F	800 °F	850 °F	900 °F	950 °F	1000 °F
Class 150	290	260	230	200	170	140	125	110	95	80	65	50	35	20
Class 300	750	750	720	695	665	605	590	570	530	510	485	450	320	215
Class 400	1000	1000	965	925	885	805	785	755	710	675	650	600	425	290
Class 600	1500	1500	1445	1385	1330	1210	1175	1135	1065	1015	975	900	640	430
Class 900	2250	2250	2165	2080	1995	1815	1765	1705	1595	1525	1460	1350	955	650
Class 1500	3750	3750	3610	3465	3325	3025	2940	2840	2660	2540	2435	2245	1595	1080
Class 2500	6250	6250	6015	5775	5540	5040	4905	4730	4430	4230	4060	3745	2655	1800

Interpolation between listed temperatures is permitted; extrapolation is not.

How far this table has been checked. The Class 400 row rests on a single secondary source. The other classes agree in two independent sources. None of the values on this site has been checked against the standard itself; see how the figures are checked.

What Group 1.9 is used for

This is the 1¼Cr-½Mo chrome-moly group. The chromium and molybdenum give the steel creep strength, which is why it is used for steam and hot hydrocarbon service at temperatures where carbon steel has faded.

Reading the ratings

A Class 300 flange in Group 1.9 is rated 750 psig at 100 °F, 605 psig at 600 °F and 215 psig at 1000 °F, which is 29% of its cold rating. Every other class in the group follows the same curve, scaled by the class. It is at or above Group 1.1 carbon steel at every temperature in the table: at 1000 °F carbon steel is down to 85 psig in the same class.

Each figure is the highest gauge pressure the flange may see at that metal temperature. To use the table, fix the material group and the design temperature first, read down to find the lowest class whose rating is at or above the design pressure, and interpolate between columns if the temperature falls between them. The rating of the flange is often what limits a line, since the pipe wall is usually good for more.

Guides and comparisons for this page

Pressure-temperature deratingReading a P-T table and interpolating between temperatures.Hydrostatic test pressureWhat a line is tested at, and what its flanges allow.Pipe material selectionA53, A106, A312 and A335: which grade suits which duty.Carbon steel vs stainless steel pipeStrength, temperature and corrosion trade-offs.Class 150 vs Class 300Dimensions, bolting and ratings of the two commonest classes.

Common questions

Which materials are in ASME B16.5 Group 1.9?

A182 F11 Cl. 2, A217 WC6, A387 Gr. 11 Cl. 2.

What is a Class 300 Group 1.9 flange rated at 600 °F?

605 psig (41.7 bar). At 100 °F the same flange is rated 750 psig (51.7 bar).

Other material groups

Group 1.1 Group 1.2 Group 2.1 Group 2.2 Group 2.3 Group 1.10 Group 1.15