You should use the new european piping code
EN 13480 (part 3 for design)
German version is designated DIN EN 13480-3:2002 and is available at
The previous DIN standard for calculation of pipes and bends was DIN 2413 part 1(Pipes) and 2 (Bends) - but after introduction of EN13480, this is no longer applicable. (In fact DIN EN 2413 is now a bolting standard)
I am not aware of any available software but most of the calculations are pretty straightforward and can be done in a spreadsheet.
The old DIN fitting and flange standards also no longer exists. The new standards are:
EN 10253-1,
Butt-welding pipe fittings - Part 1: Wrought carbon steel for general use and without specific inspection requirements
(Draft standard) EN 10253-2,
Butt welding pipe fittings - Part 2: Wrought carbon and ferritic alloy steel with specific inspection requirements
(Draft standard) EN 10253-4,
Butt-welding pipe fittings - Part 4: Wrought austenitic and austenitic-ferritic (duplex) stainless steels with specific inspection requirements
EN 1092-1,
Flanges and their joints - Circular flanges for pipes, valves, fittings and accessories - Part 1: Steel flanges, PN designated
Hope this helps
regards
Mogens