From Los Angeles Live Steamers "Engine Booster"
Reprinted in Live Steam Newsletter, September 1966
Stainless steel alloys can be divided into three groups based on their metallurgical microstructures; Austenitic, Ferritic and Martensitic.
The most widely used group is the Austenitic which has the highest resistance to corrosion in the stainless steel family. The steels in this group ossess the greatest strength and oxidation resistance at elevated temperatures, yet retain their ductility at temperatures approaching absolute zero. The presence of nickel changes their fundamental structure and nature, lowering their thermal conductivity, approximately doubling their coefficient of expansion, and making them non-magetic. They are well known for their inability to be hardened by heat treatment. These steels owe their corrosion resistance to the formation of a thin but strong transparent surface oxide film. Stainless is strong and ductile in the annealed condition, but the strength may be raised greatly by cold working. Most types of stainless teels can be drawn, formed, bent and upset easily.
The Austenitic stainless steels have good creep strength, resist oxidation and maintain corrosion resistance at elevated temperatures. Types 304 and 316 are among the strongest of the Austenitic steels and are probably the most useful at temperatures up to 100 to 1400 Farenheit. Above these temperatures the most highly alloyed type 310 is superior because of increased resistance to scaling.
The stainless steels can be joined by the conventional arc and resistance welding procedures without difficulty. A properly welded joint in chromimum-nickel stainless steel is equal to the parent metal in ductility, strength and corrosion resistance. Soft soldering or silver brazing is generally used as a sealing operation to close a lock-seamed or riveted joint. Soldering and brazing stainless steel is not difficult if the surfaces are clean and a suitable flux is used.
Used for Steam Lines
Have you ever considered using 300 series stainless steel tubing for general plumbing outside of your boiler, that is, lines exposed to the outer air?
Steam lines which are surrounded by air, particularly if it is moving air, can loose an amazing amount of heat if the lines are copper because of the rapid flow of heat through the thickness of the metal. Remember that copper has a very high conductivity to heat and electrical flow and this fact can work against you as well as for you.
Stainless steel, on the other hand, has a very low conductivity for a metal and thus retards the flow of heat through the metal. In effect, compared to copper, stainless steel has a built-in insulation jacket.
300 Series stainless steel tubing is very ductile, soft solders and silver brazes beautifully, and can be procured in a range of sizes far beyond those available in copper.