79 years in service is nothing unusual for a steam loco outside the US. When I started my apprenticeship I was working on engines that were all close to 100 years old. As ElViejo notes, if you have a well-equipped, well-staffed workshop you can keep them going for a long, long time.

As for the double smokestacks, Lost World is incorrect in saying that only 4-cylinder articulated engines were normally fitted with these. Many modern rigid engines in the US and the rest of the world had them, to improve draughting and reduce cylinder back pressure. Union Pacific 844 is a good example. And as for Garratts, the only examples to have double smokestacks were the Algerian passenger Garratts, and the related engines in Senegal and the Ivory Coast, all built by Societe Franco-Belge. All other Garratts had single stacks.

H199 has double stacks because it has two independent sets of cylinders, one for the adhesion engine, and one for the Fell system grip wheels. Each set of cylinders had it's own blastpipe and smokestack.

After thinking long and hard, I came to the conclusion that the dents in the cab side panels were put there deliberately to stop the panels vibrating when the loco reached speeds that achieved resonance in them. Imperfections such as dents break up resonances in large flat panels.

The Loco has Stepenson gear - not uncommon 1875, but almost obsolete in 1956. The Loco seems to be under steam. It seems, that steam is coming out a source in front of the cab. Has anyone here seen a H class from near: Is there a safety valve or any other steam outlet on this place? Near a working safety valve nobody would stood so relaxed.

80 Years of service is for a well-maintained steam loco not uncommon. In Germany (Isle of Ruegen) there are several engines this age still in all days use, and in Romania (I've been there several times in the 90's) I also met engines built by Krauss Linz in the 1890's.
The dents in the cab could come from something rude loaded fuel.

Wikipedia has the history. The reason that the H class lasted 79 years was because they were unique; using the Fell system to propel trains over a 1:15 incline. The end came in 1955 when the Rimutaka tuneel was built.

A feature normally seen only on locomotives with four cylinders and double sets of drivers: mallet, simple articulated, or beyer-garret types, all of which are far larger than this tank engine. In this case each cylinder had its own exhaust nozzle. Strange. Well maintained machine, I give it that.

If you have a machine shop and a foundry, you can keep a locomotive like that going practically forever. Of course, after a long enough period, the only original part on it might be the number plate.

All the sheet metal looks shiny and smooth except for the cab sidewalls. It looks as if it was attacked by a massive hailstorm, or did the crew have a coal-throwing melee?

[Parking lot door-dings. - Dave]

I've been in service since 1934 -- that's 80 years!

I'd have to say, 79 years of service is pretty remarkable.