ASME SA789 /ASTM A789: Standard for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service.
ASME SA790 /ASTM A790: Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Pipe.

Duplex and super duplex stainless steels are weldable.
Standard duplex: UNS S31803, S32205
Super duplex: S32750 (2507), UNS S32760

The differences between duplex/super duplex pipes:

WHAT IS DUPLEX STEEL?
Duplex stainless steel (UNS S31803/UNS S32205) has been developed to overcome the issues of the 300 series stainless steels, it has stronger resistance to seawater corrosion compared to stainless steel 316.
Note that, despite Duplex stainless steel shows good high-temperature oxidation resistance, 2205 suffers from embrittlement if kept at temperatures above 300oC for some period of time. (a situation that can be rectified only by a full solution annealing treatment). For this reason, Duplex stainless steels are never used for temperatures in excess of 300oC.

UNS2205 duplex steel finds application in marine projects, oil & gas exploration, closed loops water systems, desalinization plants, hydrocarbons storage and transportation, downstream refining, pulp, and paper.

SUPER DUPLEX PIPE, WHAT IS SUPER DUPLEX?
Super duplex stainless steel is a variation of the duplex steel alloy which is used in the oil & gas, chemical, power generation, mechanical and desalination industries. The higher chromium and molybdenum content of Super Duplex compare to Duplex makes it extremely resistant to uniform corrosion by organic acids like formic and acetic acid. Super Duplex also provides excellent resistance to inorganic acids, especially those containing chlorides.
Duplex steel Pipe & Tube Chemical Composition:

Grade	C≤	Mn≤	P≤	S≤	Si≤	Ni	Cr	Mo	N	Cu
S31803	0.03	2.00	0.03	0.02	1.00	4.5–6.5	21.0–23.0	2.5–3.5	0.08–0.20	-
S32205	0.03	2.00	0.03	0.02	1.00	4.5–6.5	22.0–23.0	3.0–3.5	0.14–0.20	-
S32750	0.03	1.20	0.035	0.02	0.80	6.0-8.0	24.0-26.0	3.0-5.0	0.24-0.32	0.5
S32760	0.05	1.00	0.03	0.01	1.00	6.0-8.0	24.0-26.0	3.0-4.0	0.20-0.30	0.50–1.00

Duplex steel Pipe & Tube Mechanical Properties:

Mechanical properties	Tensile,min,ksi[MPa]	Yield,min,ksi[MPa]	Elongation,%(min)	Hardness,HB(max)
S31803	90 [620]	65 [450]	25	290
S32205	95 [655]	65 [450]	25	290
S32750	116 [800]	80 [550]	15	300
S32760	109 [750]	80 [550]	25	300

Duplex Stainless steel pipes are manufactured according to the ASME B36.19 standard.
DUPLEX PIPE：S31803 Pipe, S32205 Pipe
SUPER DUPLEX PIPES: S32750 Pipe, S32760 Pipe
Duplex pipes and Super Duplex pipes match the following fittings materials: ASTM A815 (butt weld fittings) and ASTM A182 F51 / F53 / F55 / F60 (flanges / forged socket weld and threaded fittings).