Thanks for the informations about boilers in the U.S.
I will add only a few things on boilers in Germany.
Welded boilers appear as standard first after WW2, so the large boiler exchange program by the german federal railways came, as the death of steam was unstoppable, to late to change something with new technology.
Usually problematic was the welding of the fitting parts at the outer edges of the firebox shell to the tubular boiler hull, the firedoor and some other mounting parts like the dome of the boiler with the throttle valve in it. After the overcome of several problems, new, completely welded boilers were developed and a replacement program between 1957 and 1965 was undertaken, so spend several high need series of steam engines a fully welded boiler. Steam locomotives build after 1952 usually were fitted with a welded boiler, but still small series of boilers, especially for industrial railways or industrial private shunting were found with riveted boilers.
During WW2 germany was short on copper, because this was need in military warfare purposes, so many boilers were refitted with a welded firebox from steel, so welding appeared step by step, leading to the build of very improved boilers by Henschel in hesse.
After 1952 the engineer at Henschel development department, Dr. Tross, found several specials on welding technology, like better welded stays and crown bolts and the development of high output boilers, like for the SAR Series 25 and 15 made Henschel locomotive works very famous.
Because of having till the end of steam in Germany a various mix of different, but standardized locomotive series, steam locomotives there was a co-existence of riveted old boilers, like on former prussian railways series locomotives or on non-boiler replacement program included series of heavy freight locomotives series 44, and fully welded boilers, like series 41 and 01.10
The locomotives were usually withdrawn from service and set out of service on heavy boiler failures, because most shops were still able to maintain a riveted boiler, but the work was time consuming and needed much more labour, than welded boilers - so this was the main argument to replace a locomotive with a new diesel or electric type, so it was often used, even in the boiler did not need any rivet maintenance of rivet replacement. On the other hand, on several riveted boilers one can find cut parts with newly welded in patches. Welding made boiler repairs more easy, so cutting a part of the boilers shell and welding in a new patch was a common practice in many shops. Usually shich patches were found on the firebox and firebox shell and the bottom of the main tubular boiler, were high corrosive parts of the boiler water accumulate and lead to long term material failures, which need material replacement.
Also Mannesmann tube works delivered many boiler smoke tubes, it was later in Germany common to weld the tube ends with prefabricated contract and prefabricated widened ends, which were welded on the tube ends. Prefabrication of those ends was more easy and better to handle, as working with the fully length tube in the tube works of the shops.
Allways keep two-thrid level in gauge and a well set fire, that's how the engineer likes a fireman
(sorry, please be patient - this 'freight train' may start slow )
