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Class 300/600 flanges

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wfn217

wfn217

Chemical
Aug 11, 2006
101
Is it a violation of ASME B31.1 to use both class 300 and class 600 flanges in the same line?
 
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Not if the service conditions stay within the 300 class limits. In that case, the 600 class flanges are just an "over-design."

If the service conditions exceed the 300 class limits are are more appropriate for 600 class flanges, the 300 class flanges are "under-designed" for the system. Not a good situation.
 
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No.

Different materials may require / permit different flanges. Nothing prevents the application of the lower class where the material is suitable for the pressure and temperature. for example, a stainless steel instrument may require class 600 where the carbon steel materials are compliant at class 300.
 
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It is not uncommon to have a spec break in a line. This is especially common at a block valve. The case may exist, that when the valve is closed, there is a potential for higher pressure on one side of the valve than the other. As a result, it maybe appropriate to have 600 # flanges on one side and 300# flanges on the other side. Of course, in this case, the valve would normally be 600# to satisfy the conditions on the higher side. All flanges should be designed to handle the conditions that they could be expected to see.
 
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No.

We use a minimum of Class 600 flanges on all of our valves on Class 150 and 300 lines. For the most part, it makes the stock room a little less crowded, and the field guys can take less stuff in their trucks when they go out. The difference in pricing is more than made up in less stock and less "oh, I need a Class 300 valve...be right back" moments.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
 
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Yes, but don't fact-to-face connect a 300 flange to a 600 flange. If the connection joins two systems of different pressure ratings, a block valve (rated to the maximum pressure of the two systems) is required as separation and pressure protection is needed to stop the possibility of overpressuring the low pressure system.

BigInch[worm]-born in the trenches.
 
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A 2" 300 and a 2" 600 will bolt together. a lot of people go ahead and match the pipe with the flange so they don't have to worry about re-certification down the road if the line is put into a different service. Bottomline just keep track of the system rating and not rely on memory.
 
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Bolt tolerance can't be the real issue? But with that said, I may be wrong, but as I recall even a <= 2" ANSI will not bolt to a <= 2" DIN (at any pressure rating).

BigInch[worm]-born in the trenches.
 
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Ashereng mentiouned the use of Class 600 flanges on all valves on Class 150 and 300 lines. Class 300 minimum was a common requirement within the oil companies for globe control valves. Fisher and Masoneilan typically furnished globe control valves rated for Class 600 applications up to about 6 NPS, thus only the flange limited the pressure class application. I would not bet on this as a current fact but it is a reasonable requirement for smallish globe control valves.
 
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I think that Class 300 is still often the minimum for flanges on control valves and block valves. The reason is a thicker flange. Class 150 flanges, in addition to being thinner, is a 4 bolt. It is not as robust.

Having said that, in many utility and off-site services, Class 150 are used.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
 
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I worked for one gas company that was stubbornly using 900# when only 600# were needed, but only in their offshore systems. They were new to the offshore sector and their reasoning was, "their partners standards required it". When they started doing their own offshore pipelines, I convinced them that 600# would do fine and the "old rule" was changed. Later, when I worked for the "other" gas companies that were responsible for influencing the first company's design, I did the same thing, but telling them that their old partner had changed that standard. That happened 3 times (4 total). As far as I know, nobody is using 900# where only 600 is needed now (please let me know if that isn't the case). My opinion is that a 150# with 4 bolts is still 1 bolt more than you need. If there was or were to be a problem, I would suspect corrosion, or that somebody didn't consider surge.

BigInch[worm]-born in the trenches.
 
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NPS 1/2 - NPS 3 are the same flanges in class 300, 400 and 600; so are the gaskets.
 
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Most users allow NPT for 1-1/2" and smaller pipes. Some allow up to 2" NPT. A very few allow 3" NPT.

I am not sure when you would use a NPS 1/2 with a flange. Can you give some examples?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
 
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The only threaded pipe my site allows is limited use in utilities and only up to 2" max...though there is a little of 6" threaded on an old water deluge system. Process pipe is welded. Two inch and under carbon steel pipe is almost always socket welded.
Examples of 1/2" flanged pipe? Orifice flange taps, seal flush connections on API pumps, low pressure steam tracing systems...really not unusual at all.
 
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I agree with bingopin.

Few users permit threaded line class fittings in hydrocarbon service. It is common for the first block to be welded or flanged with threaded fittings for the instrument interface. I have not been on a project that permitted threaded piping valves and fittings on the B31.3 side of the instrument interface for well over a decade.
 
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Thanks bingopin.

In many of our projects, we thread 2" and under, and yes, hydrocarbon service. There are some flanges of course, though not many at 1/2" or 1".

I also noticed that many of the fittings and valvs off our "christmas tree" are threaded (up to 10000 psi WOG).

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
 
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