Pressure Rating?

Hi,

I just need to ask

* What actually is meant by Pound rating of pipe fittings and valves like 500, and for SW fitting 3000 ...

and why it is designated as being used; I mean why cant we have SW fitting of 2900 pound rating

Cheers

(c&p) Perhaps this will help;

If you go back far enough in history ( the following information is derived from " Marks Handbook, 4th edition, 1941)
There were 3 classes of cast iron flanges rated as "American Standard"; 25 Lb, 125Lb and 250Lb.
They were listed as.
American Standard Cast-iron Pipe Flanges and Flanged Fittings
For Maximum Working Steam Pressure of 25Lb., 125 Lb, and 250Lb per Sq.In. (Gage)


. These ratings roughly corresponded to the nominal ratings of the iron pipe available at the time; Standard Pipe, Extra Strong Pipe and Double Extra Strong.

These eventually evolved into the Schedule10, 40, 80, and 160 pipes that we have today.
The Flanges have evolved into the ANSI flanges of today, but the labeling stayed similar.

At the time the engineer had to really design his system because the terms Standard pipe, Extra Strong Pipe etc. were dimensional standards, the pressure rating of the pipe was based on material and manufacturing. For instance Grade B seamless had a higher pressure rating than "Grade B Electric fusion welded steel per ASTMA155" but Grade B Electric fusion welded steel had almost the same pressure rating as "Lap-welded steel per ASTM A106. Marks lists 27 types of fabricated pipe from Seamless steel to Cast Iron and differentiates the cast iron as centrifugally cast or pit cast.

An interesting side note, the size ranges included in the standard at the time..
25 Lb. Flanges. 4" to 96 " pipe size

125Lb. Flanges... 1" to 12" pipe then 14" O.D. to 96" O.D., the 96" used (68) 2 ¼" bolts on a 108 ½" bolt circle. Oil Field stuff.

(c&p) This too could help;

The question you raise fits together with another historical question concerning the origin of the specific dimensions of pipe schedules. We have never found an authentic historical account that explains either. Because we have the same curiosity as yourself, and since we have known and had conversations with some of the people ( now deceased ) who worked on the earliest API Flange Specifications, we will offer a “speculative history.”

All flanges seem to have originally derived from pipe. Pipe nominal sizes like 2”, 3”, and 4”, when originally standardized, had approximately 2”, 3”, and 4” inside diameters. Flanges, as originally standardized, had their nominal sizes designated according to the pipe with which they corresponded. As industry found the need to contain higher pressure, standardized pipe needed thicker walls to contain this pressure. This resulted in “schedules” designating wall thicknesses on given outside diameters of pipe, these outside diameters now fixed in size with the advent of standardized pipe threads. As electric arc welding became a common procedure, Welding Neck Flanges became available with necks and inside diameters to match the various “schedules” of pipe.

For oil and gas well use, flange connections needed standardized bores so that standardized tools could pass through these bores. In contrast to pipe, flange design allowed the necks of flanges to increase in size to allow thicker walls to contain higher pressure, keeping the working bore's inside diameter the same. Pipe “nominal” size to flange “nominal” size “tradition," along with the fact that API adopted ASA flange face and thickness dimensions for 6B flanges, resulted in the original flange designations, e.g., 2” Series 1500, with 2-1/16” bores. Flanges with 2-1/16” bores would pass tools 2” in outside diameter; 4-1/16” bore flanges would pass tools 4” in outside diameter, and so on. As standardization continued and specialized requirements presented themselves, bore sizes like 7-1/16”, 11”, 13-5/8”, and others developed. Higher pressure requirement also contributed to the need for new flanges, and in the 1950’s, API adopted 6BX flanges for this purpose.

For years 6B flanges had their sizes designated as nominal 2”, 3”, 4”, 6” etc. With the advent of 6BX flanges, API designated flanges by bore and working pressure.

Some history on flg ratings.


www.woodcousa.com/flange_history.htm