Pipe flanges for small diameter pipe 1

[bush47]

Many engineering pipe specifications will specify the use of 300# flanges for pipe diameters of 3" and below for pipe classes specified for 150# service. Does anyone know the basis of this? I havve heard it is to provide the smaller pipe more structural strength and resistance to vibration issues.

 

[pennpiper]

Statement:
"Many engineering pipe specifications will specify the use of 300# flanges for pipe diameters of 3" and below for pipe classes specified for 150# service. "

In my more than 45 years in Process Plant Piping Engineering and Design I have NOT found this to be true.

Unless it is something very, very special these sizes and ratings have all used "Unions" for removal assembly joints.

 

[europipe]

Bush,

Pennpiper is correct,
Your company is an exception in pipespecs.
Maybe it is done for later upgrading of process systems.
150# specs use 150# flanges for all sizes by other companies.

Greetings

 

[BigInch]

The basis of that is a MISTAKE that has been cut and pasted into the documents you've been reading lately.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[bush47]

Based on your replies there is no basis for using the 300# flanges for the smaller sized pipe for 150# service. If this was a cut and paste mistake than it appears to be infectious because I have found this in specifications from Foster Wheeler, "Ford, Bacon & Davis", CB&I/TPA and in old Mapco and Premcor refinery specifications. It may just be a refinery specific requirement.

 

[BigInch]

There is no basis for it other than to provide extra mechanical strength when needed. I think its over the top to provide the next higher class rating and would prefer to do something like specifying XXS pipe as a minimum and increase the bore of the flanges to match, when such piping is to be used to fabricate a gas piping blowdown vent, or similar application where stresses are likely to be higher than the norm. Maybe that's not likely to carry the higher moments that a extra class flange would handle, but the piping is likely to be the weakest link-stress wise. If you're trying to stop leaks with an extra class flange, I would think it would just cause a nearby 6" flange gasket to blow first. No gain there. Asking for extra class factor, without necessarily specifying a greater wall thickness is not likely to achive the desired effect anyway, as the pipe with a wall thickness matching the pressure requirement might not be able to transfer the full moment of a flange that has been increased one class higher. Where's the advantage of specifying one component to a higher standard, when the connected pipe is not speced in the same manner.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[bush47]

BigInch,
Thanks. Great information. When I see these types of changes in specifications, I scratch my head and say why did they do this. As you said I see no advantage to going to the higher class to to provide more available bolt load for seating stress. Typically at these smaller flanges there is plenty of bolt load available to seat the gaskets and have a leak free joint.

 

[unclesyd]

You will find that specification no Class 150 flanges on small process or utilities piping in our piping specs. We also require a Class 300 flange on any system using Spiral Wound Gaskets.
We permit no unions in alloy piping systems and if one is used in CS it is on a case by case basis.

I know of two other very large chemical companies that have very similar piping specifications.

 

[unclesyd]

After reading the post by BigInchI should add to my post that all our small piping is Sch 40 or heavier. This includes all our SS piping.

One problem not mentioned is with Class 150 flanges, especially in SS, mechanics have been know to roll or cup a flange and when using a Teflon gasket you have problems.

 

[bush47]

Just receieved some information from one of our other refineries. The purpose for going from a the 150# to the 300# class was to eliminate using 4 bolt flanges (3" and below for 150# flanges). The concern was a reliability of a flange if one bolt is lost (due to damage, corrosion, or defective bolt). The 2" and 3", 300# flanges have 8 bolts and loss of a bolt is not as critical.

 

[moltenmetal]

If the loss of a flange bolt in a 150# 4-bolt flange is worrisome to them, what must they think of all that German equipment with the 2-bolt flanges on it? Or what about Grayloc hubs, Victaulic couplings or sanitary fittings?

I've seen this anti-150# prejudice before but never understood it. I don't know if anyone has calculated the cost versus the benefit of such a spec, pushing every flanged valve or instrument in the line up to 300# etc. Personally I have no hesitation using a 150# flange set at any size in a 150# line. We experience no problems with these flanges with spiral wound gaskets either.

Avoiding unions in alloy service? That I can understand. The only unions we permit are in CS, and then only with a brass seating ring. Even after lapping, alloy unions are a 1st order PITA.

 

[BigInch]

A lot of offshore pipelines in the GOM in the early 80s arbitrarily used 900# class where only 600# was required and 600# where only 300# was needed. Enron was one of them. I got them started using the proper flanges with no ill effects that I've ever heard of. I think even Transco changed after that. I follow the logic I've already mentioned above, again with no ill effects that I'm aware of, then again why put a 2" pipe somewhere a bolt is going to get knocked off? Seems like the pipe and flange would be damaged before you kicked off a bolt without hurting those. Leaves me to believe that the gasket integrity was the only worry. Well, I guess its only a 2", so whatever floats your boat....

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JLSeagull]

A commonly specified control valve requirement is for globe style bodies smaller than NPS 6 to include Class 300 minimum flanges. I think that the pricing for Class 150 and Class 300 is usually the same for smaller globe style control valves in carbon steel.

 

[SNORGY]

I just ran across this very issue last night in a client piping specification. Therein it was specified that 300# flanges in 3" NPS and smaller could be used in what was otherwise a 150# line class. There was a note number in the "Notes" column that linked to a note on the second page, where it was stated that the 300# flanges were primarily intended for equipment connections that required them; presumably this might include control valves as mentioned in one of the posts above.

I prefer resolving such situations via notes and markings on the drawings that identify the off-spec flange pair.

I have seen some clients express a preference for 300# flanges in small lines in order to achieve what they perceive to be better joint tightness in hot lines such as heat medium glycol or heat medium oil, which tend to be difficult services to seal once a leak path develops.

To me, the best answer is in proper fit-up and alignment and adequate regard for piping displacements and supports to ensure that a 150# flanged joint maintains its integrity throughout the operating range. We have probably all seen situations where the "solution" was "get a bigger snipe and yank that sucker together and really reef on those nuts.". It does work, but one has to think that there's a better way.

Regards,

SNORGY.

 

[cvg]

Indeed I have, 30" flange, contractor used a wrench with 10 foot long cheater bar and a backhoe to push on the bar - just to get the gasket to seal. Solution was to reject the flanged fitting and get a new one that fit and sealed properly...

 

[BigInch]

We all know that after they do all the larger flangeups and finally get down to the 2" stuff, op guys simply don't like seeing only 4 bolts.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rmw]

I had a client once whose maintenance foreman used a 900# flange on a 15 psig steam deaerator pipe - I think it was 2 inch pipe. He had come from the old field where a lot of stuff was higher pressure and he brought this 'more is better' mentality with him. He was highly insulted that I challenged him on this. Every time I went by that equipment I just shook my head. His (bosses) money........

rmw

 

[rneill]

I have seen this requirement before as well and was told it had to do with the bolt pattern on the flanges and the integrity of the connection in a fire. However, I remember reading an API report on fire resistance of flanges many years ago and as I recall it didn't support this theory.

It may also have something to do with the whole issue that most spiral wound gaskets don't meet code calcs in class 150 since you either exeed the allowable stress of the bolting or you have insufficient seating stress on the gasket. The manufacturers make low stress 150 spiral wound gaskets but these are rarely used and we almost always look the other way on this issue. Perhaps they have done some analysis and determined that this is a signficant problem on the small bore flanges and they want the additional bolt load area ?