class descriptions

I don't remember where I have seen this and it will take me a long time to do the research to find the definition for the different designations. Even then I don't know if it will satisfy you.

I will give you my version.
- 150 lb = This is the old tried and true manner of designating a 150 Pound Flange rating. The "lb" is just the English language abbreviation for "Pound" and is based on the Latin word "Libra".
- 150# = The "#" is just a sign for Pound. This was quicker and easier to use on drawings.
- Class 150 = This is the more current and more acceptable form for designating a 150 Pound Flange rating.

All three mean the same thing.
I hope this helps.

Screwed and Socket-Welded Fittings

These fittings perform the same function as the Butt-Weld fittings. There function is the same but the method of joining and the dimensioning is different. Normally these fittings are used in sizes 1-1/2" (or 2") and smaller. Welded fittings are specified the same as the pipe, by weight, schedule or wall thickness. Screwed and Socket-Weld fittings are specified per the pressure class.
Thread engagements as well as the depths of the sockets for different pipe sizes are different and must be looked-up on an approved dimension table.

Threaded fitting pressure classes:

· 125# Cast Iron
· 250# Cast Iron
· 150# Malleable Iron
· 300# Malleable Iron
· 2000# Forged Steel *
· 3000# Forged Steel *
· 6000# Forged Steel
* Most common

The Cast Iron and Malleable Iron fittings are basically used for air and water services at a low temperature and pressure. Forged fittings are normally used for higher pressures and temperatures as well as for the more complex commodities.
The majority of the screwed fittings will have female (internal) threads per NPT (National Pipe Thread). The exception will be the swages and the plugs - they will have male (external) threads.

Socket-Weld fittings are manufactured in two classes.

· 3000# Forged Steel
· 6000# Forged Steel

Socket-Weld fittings have a deep socket into which the pipe slips and aligns itself. The weld is then made on the outer surface of the pipe and fitting. This eliminate the need for or use of special clamps or tack welding for alignment prior to the final fit-up welding. At the bottom of the socket a 1/16" gap is left to compensate for expansion when the weld is made. This gap is called a root-gap. The swage does not have an internal socket; it will fit into the socket of a fitting or be butt-welded to a pipe.

The dimensions for screwed and socket-weld fittings must be looked up on a standard fitting dimension chart. There are no dimension short-cuts for these fittings.