Piping Classes Origin ? 2

slazzi:

Take a few stress pills and relax. You are wandering through a world dominated by mechanical engineers. It is their method of identifying pounds force per square inch gauge without having to say it as such.

Piping class numbers typically indicate the flange class. Pressure ratings depend on material and temperature.

For ASME B16.5 made from Material Group 1.1

Temp -20 to 100 deg F


#150 285 psig
#300 740 psig
#600 1480 psig
#900 2220 psig


Take a look on the web and you should find a complete list.

Stolen from thread292-77429

bvi (Mechanical) 18 Nov 03 9:29
Class and NPS are designations, not measurement units (e.g. Class 150 and NPS 4). Thus, there is no point in making a US Conventional Units to SI units conversion. As such, Class (e.g. Class 150) and NPS (e.g. NPS 4 for a pipe with a 4.5 inch OD) are used both in the SI unit portion of the new B16.5 standard and in the US Customary Units portion of the standard.

Note that Class pins down the geometry of the flange. The pressure rating depends upon the material of construction and the temperature.

As for designations of # (150#) vs Class (CL-150) that goes back about 30 years. In the 1968 edition of B16.5, the ratings are given for pound (lb) classes. By the 1977 edition, the ratings are given by class (CL-). I suspect that the change actually happened in the 1973 edition, but I don't have that ed.

Now for what relationship the flange classes have to their ratings: There is a relationship. The flange class plays a role in the formulas used for bolting cross sectional area, wall thickness, and flange rating. For example, the wall thickness formula is the usual variation of t=pr/S with p being the flange class as pressure. Interestingly, the flange rating approach for CL-150 is different than that of the other classes. Take a look for yourself in Annex B (pg. 103) of B16.5 2003 (Annex D for those of you still using the 1996 ed.)

jt

I have never understood the class ratings either. I suspect that at some point it the distant past, a "150 lb" flange was actually good only for 150 psi. Now and days, with more modern materials and manufacturing methods, it is good for higher pressures. Someone mentioned to me that the "150 lb" designation was related to some kind of machining operation, but I doubt it. Maybe someone out there knows the source of the designations.

Use the metric PN system: 20, 50, 100, 150, 250, 420 at least then you know it's bar a at a temperature of -30 to +120 deg C. Just a thought.

Steve Jones
Materials & Corrosion Engineer

I can't back it up with a document, but I've always believed that '150#', etc., was a reasonable working pressure for pipe and flanges made of cast iron.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

The classes once corresponded with classes of boilers.

The boiler manufacturers standardized (more or less) on steam flanges around 1928. Many of those flanges were in fact, threaded, and the rating extended itself to ensure that 750 PSI flanges didn't end up with 300 PSI pipe on them. When they started welding flanges, they were still slip-ons or Socket Mount, which led to filled welds, and no particular gain in strength or fracture toughness.

Flange design is really and largely clamped gasket design, which is obviously dependent on the gasket's elastic and plastic characteristics and those of the bolts. With Gray Iron, its also dependent on the limited ductility of GI. The temperature effect both the Material Properties for all the components and the initial vs operational deformation on gaskets and bolts...As would be the case for many operational steam boilers, these stresses and deformations would cycle through the Big Delta associted with Temp and Pressure; and small deltas associated with equipment vibration and similar.

So it took the first few rounds of research on fatigue as a failure mechanism, before they limited the use of low ductility materials. That led to the Low Class for GI flanges.

So using Weld Neck Flanges; very high torques on high strength bolts; weld neck flanges with backing rings; high spec gasket materials, and limiting the temperature and pressure cycles in service; and a 300 PSI stainless flange will quite contentetdly act as the discharge flange for a 1250 PSI Hydraulic Pump.

Curious thing, the abbreviation is like in Spanish “pound” is “Libra”; “pounds” is “Libras”, abbreviation in Spanish is: “lb” or “lbs”. About the dimension, I suppose people just get tired to call then class “150 pounds per square inch”, and only call them “150 pounds”, mechanical people do that very often.

Regards

admt63

It isn't a curious thing that the abbreviation for "pound" is "Lb". It has a factual reason: it comes from the Latin term for pound, which is "Libra". Most of the Italian, Spanish, French, and Portuguese languages is derived from the generic Latin language - hence the term "Romance" languages (from Roman, or Latin). A lot (some say as much as 40%) of our present-day English is strictly derived from the Latin, via the conquest of William of Orange over England - which forcibly introduced French into the English culture and thereby, Latin-derived terms. The rigorous study of Latin in British schools was maintained for many centuries (& may still be) as a cultural and linguistic tool.

The British moved to SI units, thus reducing the confusion of such English Unit terms. Still, at jobsites I find that the Scottsmen use "stones" when speaking of weight.

John

Gentlemen

For your interest, the origins of latin in England

Latin was the language spoken by the ancient Romans. As the Romans conquered most of Europe, the Latin language spread throughout the region. Over time, the Latin spoken in different areas developed into separate languages, including Italian, French, Spanish, and Portuguese. These languages are considered “sisters,” as they all descended from Latin, their “mother” language.

In 1066 England was conquered by William, duke of Normandy, which is in northern France. For several hundred years after the Norman invasion, French was the language of court and polite society in England. It was during this period that many French words were borrowed into English. Linguists estimate that some 60% of our common everyday vocabulary today comes from French. Thus many Latin words came into English indirectly through French.

Many Latin words came into English directly, though, too. Monks from Rome brought religious vocabulary as well as Christianity to England beginning in the 6th century. From the Middle Ages onward many scientific, scholarly, and legal terms were borrowed from Latin.

During the 17th and 18th centuries, dictionary writers and grammarians generally felt that English was an imperfect language whereas Latin was perfect. In order to improve the language, they deliberately made up a lot of English words from Latin words. For example, fraternity, from Latin fraternitas, was thought to be better than the native English word brotherhood.

The term is actually "Class" 150, 300, 600, etc. The origin of the numbers (150, 300, 600, etc) was the pressure in psig at the corresponding saturated steam temperature. The ratings are different today due to change in materials and flange design.

Here is an excellent site that has some information on the API and ANSI relationship. The online tools are very good in makeup and identification of API flanges.