Blind FF mating RJ flange 2

[ElCidCampeador]

Hi,

according to a new disposition of my client, I have to close a blind RJ flange 6" #300 with a carbon steel blind FF from plate Thk.10mm. Then the entire piping line (where this flange is present) will be filled up with nitrogen @ 2 bar and shipped.

2 questions:

-Do you think 10mm thickness will be enough? (I think yes)
-Could be a leak between FF and RJ flanges, even if I use a ring joint gasket?

More in general, what kind of problems may I face with this particular flange coupling? Thank you.

 

[LittleInch]

A class 300 RTJ is a little odd. Do you mean RF?

What type of gasket are you thinking of?

This sounds like a wholly bad idea to me. The contact points for your gasket are small for an RTJ.

Nitrogen gas can easily kill people if it starts to leak out in transit and or would dissipate and not do what it is supposed to.

To be fair 10mm plate won't bend but I don't understand why you can't use a proper blind flange and gasket?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ElCidCampeador]

I'ts a blind FF from plate mating a RTJ flange. Suppliers are closed so It's faster for us cutting blinds from plate.
For gasket I have no idea, rubber? Soft iron?

 

[LittleInch]

You're probably better off with a large O ring inside the groove if you can.

Still doesn't sound good though.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ElCidCampeador]

Still doesn't sound good though.

Yep, this is also my idea.

Anyway, I've just checked thickness (in a very approximated and easy way) for FF-RJ flange but also FF-RF flange...using formulas acc. to ASME VIII Div.I and blind should have 30mm thickness as minimum.
This to satisfy seating condition (which from calculation is the very warning point).

I could cut blind from a higher thickness plate...15mm maybe, but 30 is too much.

Do you have any suggestion to improve the safety of this (unusual) blinding system? I know, "Not doing this" would be the best option...

 

[LittleInch]

Well a 6" #300 blind in B16.5 is 35mm thick, but here this is a low pressure spade off so you're not trying to hold in 50 bar.

Only other thing is to insert an expanding plug into the nozzle as your primary seal and then add this blind as a secondary containment and paint it yellow to warn everyone.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ElCidCampeador]

Only other thing is to insert an expanding plug into the nozzle as your primary seal and then add this blind as a secondary containment and paint it yellow to warn everyone.

I can't put anything inside the vessel, the only thing that I could do is acting on the blind from outside (e.g. welding sort of reinforcement to the outside face of blind...? Or clamping in a certain way?)

Bear in mind that the blind, once arrived to the main plant, will be thrown in the trash.

 

[ElCidCampeador]

One more clarification: acc. to my software calculation "10mm Thickness is less than minimum required thickness for seating condition", so any further action should be done in order to solve this problem.

What if I use a torque control with a torque wrench?

 

[LittleInch]

Not even something like this??

10 or 15mm is good enough to hold 2 bar.

Just don't bolt it down too hard.

Hence use a soft O ring and squash it into the groove.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ElCidCampeador]

Not even something like this??

What is the name of that "plug"?...but it will take too much time to find it on the market.

 

[LittleInch]

Plumbers use them all the time.

6 inch plug (you get some err interesting options with that search) or "expanding pipe stopper"

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ElCidCampeador]

ahhhh...okok, but my client requires blinds only (bolted joint).

 

[marty007]

If seating is driving your calcs to 30mm thickness, use a very soft rubber or self-energizing gasket with very low y-value...

 

[SnTMan]

...and you may use higher than Code allowables...

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

 

[ElCidCampeador]

Thank you all for your advices.

I re-calculate using higher code allowable (close to Yield Point) and changing gasket and I reach 20mm, which is high but there's a chance to find something.

Another question: available plate would be S275 and not P275, so good for structural application but not for pressure parts...do you think that could be a problem?

 

[LittleInch]

What pressure are you using in these calculations?

Have you sourced an o ring or other gasket material

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ElCidCampeador]

What pressure are you using in these calculations?

0,3 bar...(2 bar in the first post was a precautionary value changed by client)

Have you sourced an o ring or other gasket material

Well, I'm trying to find a blind RTJ...What I verify for now is a blind FF from plate with a WN-RF (I have another 6" connection but simply RF), but plate is for structural.

Blind as flat head has stresses different from a rolled plate for shell; in addition pressure is very low, so I think that S275 (or better S355) for this application could be a valid alternative solution. Am I wrong?

 

[r6155]

Why not try with a mock up?
Rubber O-ring and 10mm plate for blind flange.

Regards

 

[ElCidCampeador]

In the end for RTJ we will put a flat asbestos-free gasket on to the inside ring between groove and inside WN central bore (leaving empty the o-ring groove), using a 20mm thk blind with smaller bolts than usually used for that flange...calculation is ok with that configuration.

Thank you all for your ideas and time.