David W. Spitzer
David W. Spitzer

Approximately how much pressure can a 150 lb. flange withstand?

A. 60 PSIG

B. 150 PSIG

C. 180 PSIG

D. 270 PSIG

It might seem logical that a 150 lb. flange would be capable of withstanding 150 PSIG (Answer B) or maybe 20 percent more (Answer C).

However the “150 lb.” in 150 lb. flange is its name — not the pressure it can withstand (pressure rating). Perhaps more basic is that the stated question is incomplete because the flange material and operating temperature are not defined. In general, carbon steel flanges have different pressure ratings than stainless steel flanges.

Industrial Automation Insider 300x250Further, the pressure that a given flange can withstand decreases as its temperature increases. The pressure ratings for 150 lb. carbon steel and stainless steel flanges are approximately the same and will be treated as such in this article. As a side note, the pressure ratings of 300 lb. and 600 lb. carbon steel and stainless steel flanges are significantly different at different temperatures. Below find a table of approximate pressure ratings for 150 lb. flanges at different temperatures.

Temperature  Pressure Rating
Ambient 270 PSIG
400 F 180 PSIG
500 F 150 PSIG
800 F 60 PSIG


Given the vagueness of the question, it would appear that all of the answers are correct.

Additional Complicating Factors
The pressure ratings of flanges manufactured per standards are published for some materials. Pressure ratings for flanges made from different materials and other dimensions may need to be either calculated and/or tested.

David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC, offering engineering, training, strategic marketing consulting, distribution consulting, and expert witness services for manufacturing and automation companies. Spitzer and Boyes is also the publisher of the Industrial Automation INSIDER. Mr. Spitzer can be reached at 845 623-1830 or via www.spitzerandboyes.com.