2000 Horse-power Installation of Babcock & Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers at the Kentucky Electric Co., Louisville, Ky.
A special grade of soft flanging pipe is selected to prevent breaking. The bending action is a severe test of the pipe and if it withstands the bending process and the pressure tests, the reliability of the joint is assured. Such a joint is called a Van Stone joint, though many modifications and improvements have been made since the joint was originally introduced.
The diameter and thickness of such flanges should be special extra heavy. Such flanges should be turned to diameter, their fronts faced and the backs machined in lieu of spot facing.
In lines other than given for pressures over 150 pounds, all flanges for wrought-iron pipe should be threaded. All threaded flanges for high pressure superheated lines 3½ inches and under should be “semi-steel” extra heavy. Flanges for other than steam lines should be manufacturer’s standard extra heavy.
Welded flanges are frequently used in place of those described with satisfactory results.
Fittings—For saturated steam under pressures up to 160 pounds, all fittings 3½ inches and under should be screwed. Fittings 4 inches and over should have flanged ends. Fittings for this pressure should be of cast iron and should have heavy leads and full taper threads. Flanged fittings in high pressure lines should be extra heavy, and in low pressure lines standard weight. Where possible in high pressure flanges and fittings, bolt surfaces should be spot faced to provide suitable bearing for bolt heads and nuts.
Fittings for superheated steam up to 70 degrees at pressures above 160 pounds are sometimes of cast iron.[78] For superheat above 70 degrees such fittings should be “steel castings” and in general these fittings are recommended for any degree of superheat. Fittings for other than high pressure work may be of cast iron, except where superheated steam is carried, where they should be of “wrought steel” or “hard metal”. Fittings 3½ inches and under should be screwed, 4 inches and over flanged.
Flanges for pressures up to 160 pounds in pipes and fittings for low pressure lines, and any fittings for high pressure lines should have plain faces, smooth tool finish, scored with V-shaped grooves for rubber gaskets. High pressure line flanges should have raised faces, projecting the full available diameter inside the bolt holes. These faces should be similarly scored.
All pipe ½ inch and under should have ground joint unions suitable for the pressure required. Pipe ¾ inch and over should have cast-iron flanged unions. Unions are to be preferred to wrought-iron couplings wherever possible to facilitate dismantling.