FFSO Flange Clarifications 2

[Packermanfan]

Hi all, I'm trying to convince the people in my office that FFSO flanges can be used in accordance with Section VIII Division 1. Apparently they have only offered RFSO flanges on Code units, even when the customer needs our units to connect to their flat plate flanges on components that are already installed. Even our subcontractor who double-checks calculations has only used raised face flanges on Code units.

Table 2-5.2 has Sketch 1a show gaskets for both flat and raised face flanges. I don't think they need to be designed as Appendix Y flanges as they wouldn't have metal to metal contact anywhere on the flange faces. But then it raises the question, should ring gaskets still be used on flat face connections, or would they be full face in that case?

Before I start suggesting things I want to have enough evidence to convince others that our "standard" designs do not have to be our only designs.

 

[jt1234]

Too many times it is not right or wrong, but the common practice so there is no benefit to argue with your people.
We found out that raised face flange is commonly made. To order FF, shop will do additional machining to remove the raised face, so why asking FF in the beginning.
We used to specify FF for internal pipe distributor, thinking it is cheaper, but then realize additional machining, we now ask for raised face slip on. Using spiral wound gasket with standard gasket seating width will make sealing much better, so why bothering full face gasket ? More seating width does not mean better, it can leak more.
Just change your mind and agree to other people to make your life easier. But nothing wrong with your thinking, keep it for yourself.

 

[GD2]

OP,
What is the flange MOC of your code units and customer's connections?

GDD
Canada

 

[Packermanfan]

@GD2 More often than not just CS SA516. If the customer requests stainless steel then we go with 304 or 316.

I just don't understand why we wouldn't offer the same connection as the customer has/is requesting.

 

[Christine74]

FF flange facings are typically specified for cast flanges with full-diameter gaskets. This is because castings are more susceptible to cracking when placed in tension, and the gap created by RF flanges imposes a bending moment on the flange. FF flanges with full-faced gaskets basically eliminate this bending moment and the associated tensile loads.

ASME Code does not prohibit FF flanges but in practice RF flanges are preferred over FF flanges for materials that aren't castings. I suspect FF flanges would be made from RF flanges that machined down, so they might actually cost more and/or have a longer lead time. That said, I would never recommend attempting to mate a FF flange with a RF flange.


-Christine

 

[SnTMan]

From memory: B16.5 permits converting a RF to FF by machining off the RF IF the required thickness (tf) of the flange is maintained.

VIII, 1, Appendx 2 permits RF of 1/16 or less to be included in the calculated flange thickness.

Above is based on older Editions. YMMV

Regards,

Mike


The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[mk3223]

It’s normally no issue to mate the RF flange to FF flange of the CS and SS material, but not cast iron.
As the request of the FF flange connection, the question is what are the details of the “flat plate flange” on the connecting components, such as material, part detail, etc. For sure to connect to the cast iron flange, it must be FF flange.

 

[r6155]

For FF flange I use ORing gasket.

Regards

 

[SnTMan]

The major part of the Job is to read all the paper, find the piece of information that doesn't match and ask the question

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

But then it raises the question, should ring gaskets still be used on flat face connections, or would they be full face in that case?

I insist: For FF flange I use ORing gasket.

Regards

 

[jt1234]

Who cares what gasket to be used as long as no leak. We built so many plants with thousands of thousand of flanges and O-ring is hardly used. We may use O-ring at 1500# or higher otherwise spiral wound is good to go. There is no issue of raised face mated with FF. The only concern is the different thermal expansion if CS mated with SS. If no way to avoid dissimilar metals, the key is to select proper bolting material, also avoid high temperature service.