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steel flat face flange to steel raised flange?

drw7162 (Mechanical) (OP)
20 Jan 11 9:20
I am putting together a calibration stand and I have a pump with a 3" 150# steel flat faced flange for the suction side and I have a steel raised face flange and gasket to mate to it.  Is this ok since its steel to steel or will I be setting myself up for leaks?  
tr1ntx (Mechanical)
20 Jan 11 9:49
Depends on the surface finish.  If it was machined with the intention of being able to seal steel-to-steel, you will be OK.
drw7162 (Mechanical) (OP)
20 Jan 11 10:12
Thanks for the replay, the mating flange to the pump simply says it meets these standards, MSS SP-25, ASTM A105, and ASME B16.5
tr1ntx (Mechanical)
20 Jan 11 14:08
ASTM A105 is the material.
ASME B16.5 is the flange construction standard.  It deals mostly with geometry, i.e., hole pattern, etc.

The flat faced flange is intended to be used with a full face gasket and won't necessarily have the same surface finish requirement as the Raised Face flange.  But just because it's not "required" doesn't mean that's not what it IS.  Give it the old fingernail test to see how similar they are.
moltenmetal (Chemical)
20 Jan 11 16:14
Depending on your gasket type, surface finish will matter a lot or not very much.  Spiral-wound gasket?  You might have an issue if your flat face flange doesn't have the 40-50 grooves per inch finish on it.  Composition gasket?  Likely no problem.

As far as the primary concern of bolting up a raised face flange to a flat face flange, that's only really a problem when one of the two is made from a brittle material like cast iron.  You'll be fine, provided you torque the flange stud bolts to give (approximately) even and correct tension.
drw7162 (Mechanical) (OP)
20 Jan 11 16:29
thanks for the info, here is the gasket i have
Aramid/Buna-N Flange Gasket Full Face, rated 1000psi
moltenmetal (Chemical)
21 Jan 11 10:20
That's a composition gasket, which won't be as dependant on the surface finish in my opinion.  Try it and see how it goes- since you're limited to 150# class, it shouldn't be a tough sealing job anyway.
rmw (Mechanical)
22 Jan 11 14:54
What piping standard governs the piping at this hookup?  If your piping comes under ASME B31.1, there is a section dealing with flange metallurgies, style (FF or RF) and bolting.  I can't speak for the other ASME B31.X standards as I don't deal with them.

In B31.1, I think it is Table 12, but that is from "senior" memory so don't trust it (I am not at my company compuer so I can't look it up.)

TBP (Mechanical)
23 Jan 11 10:08
When bolting 125 cast iron (which are inherently flat face flanges) to 150 steel (which are supplied with a raised face), B31.1 states that the raised face shall be removed from the 150 flange, and a full-face gasket used.

This is to prevent the relatively thin & brittle 125 CI flange from being sprung into a gap, while bolting-up - possibly cracking the flange.

250 CI flanges have a raised face, and they can be bolted directly to 300 steel flanges with their raised faces intact, using ring gaskets. The 250s are so heavy that unless the pipefitter has superhuman strength, they cannot crack during bolt-up.
drw7162 (Mechanical) (OP)
7 Mar 11 8:38
Just wanted to update everyone on how it went in case someone looks at this thread and wants to know how it worked.  I had no leaks at all by doing this, keep in mind my system is working under 50 psi also.  Thanks for all the help guys.
TenPenny (Mechanical)
7 Mar 11 10:32
99% of ANSI pumps in North America are sold with FF flanges, used with RF pipe.
MechEngNCPE (Mechanical)
9 Mar 11 11:12
I always write in my piping spec to "machine off raised face flanges when mating to flat face flanges"
moltenmetal (Chemical)
9 Mar 11 14:12
Yes, and this is why I hate pipe specs- they tend to address the exception by making a rule!

Mating raised to flat face is only a problem in certain material combinations.  It is not always necessary to machine off the raised face, which was the point of this thread.
rmw (Mechanical)
9 Mar 11 22:21
If you are designing to a specific code and that code is B31.1 it is mandatory to machine the RF off of the mating flange.  If your code doesn't call for it, then roll the dice.

Goulds has a particularly strong statement in their literature warning against this practice (unless, of course, the pump metallurgy is DI.)

MechEngNCPE (Mechanical)
10 Mar 11 14:56
"Yes, and this is why I hate pipe specs- they tend to address the exception by making a rule!"

-Deal with it.
moltenmetal (Chemical)
11 Mar 11 8:27
"Deal with it"

OK, I think that's permission to take this otherwise resolved thread a little off topic!

Hey, if you want to specify an expensive practice even when it's unnecessary in a particular set of circumstances, I don't have a problem with that- unless you're unwilling to PAY for it in cost and schedule.  

When the spec calls out an unnecessary practice, which is not followed because it makes no sense, and this is called out during inspection as a defect- "repairing" that "defect" is a little irksome, especially when the client themselves are inconvenienced by the delay.  The trouble is, the person who wrote the spec is seldom available to give their opinion about whether or not the "defect" is acceptable!

When the spec calls out a practice that is physically impossible, or will render their resulting unit inoperable, that gets a little comical.  And when one company's spec calls out a practice as mandatory, and another company's spec calls out the SAME practice as prohibited, that gets a little comical too.

I can tell you that it's far easier to get people to follow rules that make sense, especially when a little explanation is given in a guidance document as to why a particular practice is called out.
rmw (Mechanical)
11 Mar 11 18:33
The irony is that the rule can change within the code.  B31.1 prohibits FF CI from being bolted against RF in a 125/150 lb combination while permitting RF/RF or FF in 250/300 lb combinations.  

Another oddity:  I recently had a pump co build a pump with a 250# inlet and 250# outlet but they wouldn't put a RF on the 250# flanges (to which I was bolting a 300# flange.)  The same pump company on the other hand sold us a different model pump with 125# RF flanges.  Go figure.  I thought I was reading a typo when I first saw it.

If you are making this determination for your own plant or process, you can make rational decisions that make sense for the situation based on good engineering principles.  On the other hand, if you are making a product for sale to the public, then some end user can hire a consultant who has no sense, but who can read and quote from a code book and hang you out to dry with your customer.  Been there.  Once they find something to sink their teeth into, it seems to start a feeding frenzy where they will then go after and find all kinds of obscure stuff that amounts to nothing but that won't go away.  They bill by the hour you know.

rmw (Mechanical)
11 Mar 11 18:34
In the interest of full disclosure, I have worked as a consultant as well.

SNORGY (Mechanical)
16 Mar 11 9:16
I haven't had trouble (yet) just using a Garlock, elastomeric or other non-metal sheet-type gasket between pump suction RF and FF, but I would imagine that if the process fluid was out of the ordinary with regard to the risks of loss of containment, then it would be prudent to "engineer" the joint.

Alternatively, draw the P&ID with the notation, "125# FF (NOTE 1)", and then for NOTE 1 at the bottom left of the P&ID, state:


Then let the piping guys figure it out - which indeed they can.



TenPenny (Mechanical)
16 Mar 11 10:32
rmw, do you have any information about the statement in the Goulds literature?  I'm interested in seeing that.  Can you give a reference as to where it is?

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