Flanges - Cast iron (pump) / Carbon steel (piping) 1

[EngMecBra]

Hi,

Here I have a pump in cast iron, discharge nozzle 4" 125# FF, that shall be connected to a pipe line in carbon steel, flange 3" 150# RF.

Am I going to have any problem?

I'm worried with the possibilities below:
1 - Cast iron flange be broken during assembly due to its fragility.
2 - Cast iron "contaminate" carbon steel to be in touch.

What do you think about this situation? How can I solve this problem and finally connect equipment and piping?

Tks

Rodrigo Alves

 

[LittleInch]

Yes, you will have a problem as the flanges won't mate to each other.

You need to buy a #125 FF 4" carbon steel flange with a full face gasket to mate with your pump FF flange. Mating a FF cast iron flange to an RF flange risks breaking the cast iron flange especially if it is subject to shock loading or cold temperatures.

I haven't heard of any contamination issues, by which i assume you mean galvanic corrosion.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[MechPipe13]

another solution is to simply machine the raised face off that 150# flange.

 

[rconner]

Might want to also read the part of the recent thread at

http://eng-tips.com/viewthread.cfm?qid=341363

related to gray cast iron flange matings with raised face flanges.

 

[LittleInch]

Mecnpipe. I don't have a copy of 16.5 to hand, but is a 3" #150 directly equal to a 4" #125??.I know there are some of these different size and rating combinations that work, but would be good to confirm.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[racookpe1978]

Do not mix sizes and ratings.

 

[MJCronin]

This is discussed in "The Piping handbook" by Nayaar...

The most common solution is to machine away the RF off of the steel piping flange..

Pump manufacturers don't like to supply pumps with RF flanges (causes delays

Tightening a ductile RF steel flange against a brittle cast iron flange has ruined pump casings in the past.

These people are the experts:

http://locator.gouldspumps.com/pom_0007.html

 

[LittleInch]

Rodrigo. I've had a look at the dimensions and Unless you've made a typo in your post, there is no way a #125 4" flange will mate to a 3" #150 flange. For a start there are 8 bolts instead of 4 and the pcd is completely different.

So buy a 4" #125 c steel flange, RF if necessary and then machine the RF bit off and also a 4" x3" reducer to mate with your 3"pipework.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[EngMecBra]

Thanks for all !!

 

[tothepoint]

Another proven approach is to fit an adapter ring outside the RF of the mating flange, which essentially converts the RF flange to a FF flange. Then use an full face or Reduced Area (OPRA) gasket. Both flanges must be the same NPS and pressure class.