Alloy 20 is endorsed by relative ASME Boiler & Pressure Vessel Codes (BPVC). A variety of product forms and conditions of Alloy 20 (UNS N08020) are listed in below table which are applicable for corresponding ASME BPVC specifications and temperature limits.

Product Form & Condition	ASME BPVC Applicability & Maximum Temperature Limits of Alloy 20
	I	III	VIII-1	XII
1	NP	800	800	650
2	NP	NP	800	650
3	NP	NP	800	650
4	NP	800	800	650
5	NP	800	800	650
6	NP	NP	800	650
7	NP	NP	800	650
8	NP	NP	800	650
9	NP	800	NP	NP
10	NP	NP	800	650
11	NP	NP	800	650
12	NP	800	NP	NP
13	NP	NP	800	650
14	NP	NP	800	650
15	NP	NP	800	650

*1&2: ASTM B462 UNS N08020 forgings, annealed; 3&4: ASTM B463 UNS N08020 plates, annealed; 5&6:ASTM B473 UNS N08020 bars, annealed; 7&8: ASTM B729 Alloy 20 seamless pipe & tube, annealed; 9,10 & 11: ASTM B464 Alloy 20 welded pipe, annealed; 12, 13 & 14: ASTM B468 Alloy 20 welded tube, annealed; 15: ASTM B366 Alloy 20 seamless or welded fitting.
*I: ASME BPVC Section I Power Boilers; III: ASME BPVC Section III Nuclear Facility Components, Class 2 & 3; VIII-1: ASME BPVC Section VIII Division 1, Pressure Vessels; XII: ASME BPVC Section XII Transport Tanks. NP: not permitted.

Conclusion: Alloy 20 (UNS N08020) materials are not allowed to be used for the construction of power boilers. However, they can be used for the construction of Class 2 & 3 nuclear facility components and transport tanks with maximum temperature limits of 800°F and 650°F respectively.