Depends on the "black" steel. a 4130 type CrMo steel is much better to back purge. Also proper filler material is important with a 4130CrMo. Common practice is an ER80S-D2 filler wire. ER70S-2 is a more common acceptable alternative yet gives a slightly weaker weld joint. Yet with proper joint design, like a cluster or gusset, the cross sectional area and linear weld length compensate. Best practice is a full penetration weld to eliminate stress risers on the inside of the tubing. When full penetrating, an inert purge gas is recommended to minimize oxidation. Also best practice is a slight pre-heat to drive water out of the system minimizing hydrogen embrittlement. With GTAW (tig welding), a post heat treatment to stress relieve the weld area and heat affected zone is also recommended. This can be accomplished with an oxyacetylene torch, gently heating to dull cherry red and cooling off slowly. More professional parts are heat treated in an oven. When oxyacetylene welding 4130 CrMo tubing, this post heat treatment is not necessary as the system gets so hot it generally stress relieves and normalizes itself. Many light aircraft structures are still welded with this process. On Wed, Oct 8, 2014 at 1:17 AM, Steffen R <big.skangster@xxxxxxxxx> wrote: > Hey Marek, > > 'Formierung' is normally only used for stainless steels or titanium. > Aluminium and black steel can be welded without. > > Cheers, > Steffen > > 2014-10-07 22:30 GMT+02:00 Serge Prinz <prinz_serge@xxxxxxx>: > >> Hallo Marek, >> >> No, i didn't. >> >> Greetings from EastBelgium >> >> Serge >> >> Le 07/10/14 19:40, bnmm@xxxxxxx a écrit : >> >>> Serge, >>> >>> >>> I see that your beautiful bike is tig welded--did you back purge the >>> weld, too? ie did you protect both sides of the tubing with argon? (the >>> German term is formieren) >>> >>> >>> Cheers, >>> Marek >>> >>> >> ============================================================ >> >> This is the Python Mailinglist >> >> //www.freelists.org/list/python >> >> Listmaster: Jurgen Mages jmages@xxxxxx >> >> To unsubscribe send an empty mail to python-request@xxxxxxxxxxxxx >> with 'unsubscribe' in the subject field. >> >> ============================================================ >> >> >