Re: Why Class 150 ?

From: <Gordon.Reddek@Alcan.com>
Date: Sun May 09 2004 - 19:01:00 EDT

Davis,

Just to add to the plethora of replies on this one. My understanding is that in the dark and distant past flanges were first made from cast iron and did indeed have the rating ascribed to them like 150, 300 etc which truly meant 150psi, 300psi etc.. Apparently forged steel made and entry and so flanges with the same dimensions but made from the new material could safely be subject to a higher pressure. Now nobody wants to change a dimension standard do they, so instead of changing the flange dimensions they uprated them. Now if you are looking for ratios you will find that for all flanges from class 300 to class 2500 the pressure rating was increased by a factor very close to 2.47. So if you have forgotten the rating of those flanges simply multiply the rating by 2.47. It would appear that the class 150 flanges were particularly weak. They attracted a pressure increase ratio of only 1.89. When you look at them you can see why. They are pretty scraggly affairs with wide bolt spacing. That 2.47 is an interesting number. It gives you some idea of how much stronger steel is compared to cast iron. Marks Mechanical Engineering Handbook lists cast iron as having a tensile strength of 18-60 ksi and mild steel as 50-65 ksi. Assuming that flanges are made from the crummiest cast iron and steel and using the first value in the two ranges, that ratio of 2.47 looks about right.

Gordon Reddek
Specialist Mechanical Engineer
Alcan Engineering, Level 11, 119 Charlotte Street, Brisbane, Qld 4000, Australia.
Tel: +61 7 3218 3710
Fax: +61 7 3236 0155
Email: <a href="/group/PipingDesign/post?postID=ft1oOMPGUanCUib-Lad0HVXBTwopjm5dO8n3c0x0aoS9zv025BNuv_DVN8xayEtSTvOI_SbyPHpDlvKV2no2KYvC">gordon.reddek@alcan.com</a>

"DAVIS MCCONNICO" <tz2@msn.com> 08/05/2004 06:36 AM
Please respond to PipingDesign

         To:     <a href="/group/PipingDesign/post?postID=ATw7sWJzo-aWvZLgl58Cw6be4b-_LH9Lf4Q_oHgxZTh3TlWP4YEI0KGn_m4T3gXHZNiqpe2z_fUpbwPqm4Q7dHS7zxJbKLU">PipingDesign@yahoogroups.com</a>
         cc:
         Subject:        [PipingDesign] Why "Class 150" ?

Ok, all you pipe nerds.

Here's a dumb question.

I'm not an engineer, just a gasket salesman. But I enjoy reading this forum
and have enhanced my knowledge thereof. I've asked this for the last few weeks to all my engineer customers and no one knows.

Usually when a pipefitter (in the USA) refers to a "150 lb. flange" he means
an ASME B16.5 Class 150 flange. It's amazing how many think the "pressure rating" of that flange is 150 psig. Obviously, that's not the case. It's material and temperature dependent. For example, per table 2 of B16.5, a 304
Stainless Class 150 flange has a pressure rating of 235 psig AT 200 deg. F.
But here's my question:

Why DO they call it a "Class 150" flange? From whence was the figure "150" derived?

It's not the weight! It's not the pressure rating! I've even run some numbers from table 2 and it doesn't even seem to be the AVERAGE! (I ran an

average on the table for the 4 material groups of carbon steel, which is the
highest pressure rated group: 130 psig)

Here's hoping someone can clear up a long-standing and nagging question.

-Davis

Thermoseal Contact Information

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         Davis McConnico
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         Thermoseal Inc.
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         voice: 850 / 477-0960
         fax: 850 / 477-0106
         email: <a href="/group/PipingDesign/post?postID=Ue1qqGVXsLuYupVwmvXxhYLLJNvdm5TsGaZvzUlvpNISHZg1ACS4NWsqbbExfptt_CkU2ZVhMLrL_O9Lzz4YMcGwghZejw">dmcconnico@thermosealinc.com</a>







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[Non-text portions of this message have been removed] Received on Sun May 09 19:01:00 2004