Flanges 1

[Shaun187]

Hey guys, new here on the forum.

Stupid question, if possible, how can I connect a 125lbs FF flange to a 150lbs flange. I've checked and the PCD don't match?

Please advise

Thank you

 

[Shaun187]

a Reply to my own question, could I perhaps supply a blank flange and get them to dril to the correct PCD?

 

[CRG]

Shaun187, please check again because I believe that the pitch circle is the same between 125 & 150 flanges. If you are sure that the pitch circle is different, please state the size of flange because I would like to learn which 125/150 flanges for a given pipe size have different pitch circles.

 

[donf]

Shaun187,

I agree with CRG. The bolt circle, number and size of bolt holes should be the same. Please double check and let us know what you find.

You also need to take into consideration that you're connecting dissimiliar materials (possibly cast iron and forged steel) and should follow the rules for doing so (ref ASME B16.5, sect 5.3.5). If, in fact, it is cast iron and steel, specify the class 150 flange to have a flat face and use a full face gasket to prevent cracking the brittle class 125 flange.

One last thing. Try to get into the habit of properly describing flanges as "class 150" versus "150 lb" or "150#".

donf

 

[JJPellin]

With large steam turbines, it is common to have a class 125, cast iron, full-face flange on the turbine case connected to a class 150, steel, full-face flange on the piping. The bolting works fine under all examples that I have seen. We struggle to make sure that the fitters don't make up these flanges with spiral wound gaskets made for raised-face flanges. The risk is the possibility of overstressing and cracking the cast iron flange which is part of our turbine case. I have had to force them to remove large steam turbines in order to replace this gasket with the correct full-face gasket.

Johnny Pellin