Designated as UNS K91560, the T91/ P91 steel is a 9Cr-1Mo ferritic alloy steel with deliberate addition of vanadium and niobium, as well as controlled nitrogen content. It has outstanding heat-resistance and creep strength. It also has good resistance to corrosion, oxidation and fatigue rupture at elevated temperatures. The T91/ P91 steel is primarily used for superheater and reheater in power plant boiler construction, headers, main steam pipeline, as well as the heating furnace piping in petrochemical industry. Compared to other austenitic alloy steels, it has better thermal conductivity and thermal expansivity.

1. Equivalent and Related Standards

Standard/Grade	Product
ASTM A335 P91	seamless pipes
ASTM A213 T91	seamless tubes
ASTM A387 Gr.91	steel plates
ASTM A182 F91	forgings(valves, valve parts, flanges, fittings)
ASTM A234 WP91	butt-welding pipe fittings
ASTM A200 T91	seamless pipes(refinery)
ASTM A336 F91	forgings
ASTM A369 FP91	forged and bored pipes
NFA 49213, Gr. TUZ 10CDVNb09-01	seamless pipes for boiler superheaters & heat exchangers
NFA 49219, Gr. TUZ 10CDVNb09-01	seamless pipes for refinery
DIN 17175, X10CrMoVNb9-1	heat-resisting seamless pipes
BS 3604-2 Gr. 91	ferritic alloy steel for high temperature and high pressure service
BS 3059-2 Gr.91	alloy steels for boilers and superheaters
EN 10216-2, X10CrMoVNb9-1	seamless pipes for pressure purposes
ASTM A217 C12A	castings
ASTM A691 Gr. 91	electric-fusion-welded pipes

*The ASTM & ASME corresponding standards: i.e. ASTM A335 P91 & ASME SA335 P91, ASTM A213 T91 & ASME SA213 T91.

2. Chemical Composition of T91/ P91 Steel

Element	C	Mn	P	S	Si	Cr	Mo	Others
Content, %	0.08-0.12	0.30-0.60	≤0.020	≤0.010	0.20-0.50	8.00-9.50	0.85-1.05	*

*V:0.18-0.25, N:0.030-0.070, Ni:≤0.040, Al:≤0.020, Cb:0.06-0.10, Ti:≤0.01, Zr:≤0.01.

3. Mechanical Properties of T91/ P91 Steel

Standard	Grade	Yield Strength min. MPa[ksi]	Tensile Strength min. MPa[ksi]	Elongation min. %	Hardness Max. HB
ASTM A213/ A335	T91/ P91	415[60]	585[85]	20	250

*The tensile test shall be conducted at room temperature.
*It is 2″ specimen for the test; the elongation shall be longitudinally tested.

4. Physical Properties of P91/ T91 Steel

Temperature		Modulus of Elasticity		Thermal Conductivity	Linear Expansivity		Specific Heat	Density
°C	°F	GPa	103ksi	W/mK	10-6/°C	10-6/°F	J/kg*K	kg/m3
20	68	218	31.6	26	0.0	0.0	440	7770
50	122	216	31.3	26	10.6	5.9	460
100	212	213	30.9	27	10.9	6.1	480
150	302	210	30.5	27	11.1	6.2	490
200	392	207	30.0	28	11.3	6.3	510
250	482	203	29.5	28	11.5	6.4	530
300	572	199	28.9	28	11.7	6.5	550
350	662	195	28.3	29	11.8	6.6	570
400	752	190	27.0	29	12.1	6.7	630
450	842	186	27.0	29	12.1	6.7	630
500	932	181	26.3	30	12.3	6.8	660
550	1022	175	25.4	30	12.4	6.9	710
600	1112	168	24.4	30	12.6	7.0	770
650	1202	162	23.5	30	12.7	7.1	860

*The typical physical properties at different temperatures.