General Introduction to Alloy 20 (UNS N08020)

Alloy 20, designated as UNS N08020, is an austenitic corrosion-resistant alloy with nominal composition of 35Ni-35Fe-20Cr-Cb. It has the addition of small amount of copper and molybdenum. Alloy 20 was originally developed in 1951 for dilute sulfuric acid service. Niobium is added which makes the alloy can be used without PWHT. Alloy 20 flanges can be readily made from ASTM B462 UNS N08020 forgings or ASTM B463 UNS N08020 plates. They can be furnished in a variety of flange types including weld neck, slip on, threaded, socket welding, blind, lap joint, and LWN, etc. There are 7 rating classes available: Class 150, Class 300, Class 400, Class 600, Class 900, Class 1500, Class 2500.

Chemical Composition

Element	Wt, %
Carbon [C]	≤0.07
Manganese [Mn]	≤2.00
Phosphorus [P]	≤0.045
Sulfur [S]	≤0.035
Silicon [Si]	≤1.00
Nickel [Ni]	32.00~38.00
Chromium [Cr]	19.00~21.00
Molybdenum [Mo]	2.00~3.00
Copper [Cu]	3.00~4.00
Niobium+Tantalum [Nb+Ta]	8xCarbon~1
Iron	Remainder

*The tabulated values are abstracted from ASTM B462 Gr. UNS N08020.

Mechanical Properties

Alloy	Tensile Strength, min.		Yield Strength, min.		Elongation, min.	Reduction of Area, min.
ASTM B462	ksi	MPa	ksi	MPa	%	%
UNS N08020	80	551	35	241	30.0	50.0

*All values shall be measured at room temperature.
*Alloy 20 flanges shall be supplied in stabilized-annealed condition.

Pressure-Temperature Ratings for Alloy 20(UNS N08020) Flanges

Temp. °C	Class 150	Class 300	Class 400	Class 600	Class 900	Class 1500	Class 2500
-29~38	20.0	51.7	68.9	103.4	155.1	258.6	430.9
50	19.5	51.7	68.9	103.4	155.1	258.6	430.9
100	17.7	50.9	67.8	101.7	152.6	254.4	423.9
150	15.8	48.9	65.3	97.9	146.8	244.7	407.8
200	13.8	47.2	62.9	94.3	141.5	235.8	392.9
250	12.1	45.5	60.7	91.0	136.5	227.5	379.2
300	10.2	42.9	57.0	85.7	128.6	214.4	357.1
325	9.3	41.4	55.0	82.6	124.0	206.6	344.3
350	8.4	40.3	53.6	80.4	120.7	201.1	335.3
375	7.4	38.9	51.6	77.6	116.5	194.1	323.2
400	6.5	36.5	48.9	73.3	109.8	183.1	304.9
425	5.5	35.2	46.5	70.0	105.1	175.1	291.6

*Working pressures by classes, unit: bar.

Temp. °F	Class 150	Class 300	Class 400	Class 600	Class 900	Class 1500	Class 2500
-20~100	290	750	1000	1500	2250	3750	6250
200	260	740	990	1485	2225	3710	6180
300	230	710	945	1420	2130	3550	5920
400	200	680	910	1365	2045	3410	5680
500	170	655	875	1310	1965	3275	5460
600	140	605	805	1210	1815	3025	5040
650	125	590	785	1175	1765	2940	4905
700	110	570	755	1135	1705	2840	4730
750	95	530	710	1065	1595	2660	4430
800	80	510	675	1015	1525	2540	4230

*Working pressures by classes, unit: psig.