thread794-360799 I was looking f 4

[Big BE]

thread794-360799

I was looking for an answer regarding exactly this topic, but specifically for when the requirement to consider pass grooves came into Appendix 2. I do know that in designs from 1980-ish it is obvious when running the flanges to today's code that the gasket ribs were NOT considered, as even at 1/2 width it doesn't fly with existing bolting, but as soon as you remove the requirement to consider pass gasket it works just fine.
I am also of the opinion that when supplying REPLACEMENT parts, such as a channel or shell, but not both, that we would be able to use the original COC rules, so long as the client understands no U-stamp is possible for those parts, as they will not meet CURRENT code. When upgrading in some cases the client may even ask for B7M in lieu of B7 and of course then it may become even more important, but likely won't work with the B7M regardless.

 

[Christine74]

I take it that you are just replacing the channel and mating to an existing heat exchanger shell? As you describe that can be a problem because the requirement to account for the pass partition in the flange gasket seating calculation wasn't added to ASME Section VIII Div. 1 until Part UHX was adopted in 2004. TEMA added a non-mandatory recommendation to part RGP to account for the pass partition plates in either the 7th (1988) or 8th (1999) edition of their standard.

As I see it here are your options:

1) Advise the client that the new channel cannot meet the requirements of the current code with the existing shell flange, which will need to be replaced.
2) Design the channel per the original year of the code of construction and document it on an NBIC R-1 Repair or R-2 Alteration form.
3) You can try to chamfer the leading edge of the pass plate (don't go below 3/8 inches) in order to reduce the required gasket seating area. It might also be possible to use bolts with higher allowable stress or a larger diameter/larger root area.
4) Use an enclosed pass partition plate "box" with a removable cover so you don't have to account for the pass plate in the design of your flange.


-Christine

 

[Big BE]

Thank you Christine,
Hadn't thought of the option to fab box type pass arrangement. It's 4 pass so a little more complex...
Makes sense that TEMA was sometimes ignored for pass consideration of bolting and then UHX went and messed everything up, LOL

Yes my standard practice would be to make client aware that the bolting is insufficient for existing design. Generally when something has been operating for 40 years they will tend to just let that go. In this case it came up as well because they'd like to go with B7M instead of B7...that definitely is a problem in this case.
My engineer's first reaction was higher stress bolting, but we are also in Canada so low temp is an issue for 354-BD.
All good though, I have my plan of attack figured.

 

[Christine74]

Interesting. I've never seen B7M stud bolts specified for external bolting bolting before, only for internal bolts in "sour" service where SCC is a concern. Might want to verify if that's actually needed.


-Christine

 

[Big BE]

Yes it's a thing here. Some operators want B7M where the plant is sour, even though WE all know the environment isn't sour enough to cause issues. It's not an issue on their ANSI piping flanges so they seem to figure they can blanket everything with B7M studs, not realizing TEMA flanges are all calculated bolting, rather than legacy.
Usually we simply tell them sorry, can't use B7M for existing unless it was already that way. At least on a floating head supply we can modify the qty studs if there is room to do so.
I take issue with needing to educate engineering firms on things like this. Operators, OK I get not everyone knows little details like that, but engineering firms acting on behalf of operators should have a certain level of expertise
That's my issue though I guess...LOL

 

[SnTMan]

OP, this kind of thing is done all the time
There are ways...

Regards

Mike
.

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

 

External studs can be affected by leaks of sour fluid. Sometimes more so because of drying fluid concentrating the bad actors.

Why not substitute B7M for B7, unless it for reasons of availability? There is no downgrade in minimum strength and you gain resistance to sulphide stress cracking.


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Big BE]

??
There is no downgrade in minimum strength and you gain resistance to sulphide stress cracking.
??
there is a 20% reduction in strength per ASME code between B7 to B7M

 

[SnTMan]

Exactly. I don't get the B7M angle

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

 

Note to self: don't rely on memory for Code details.

The point remains, when SSC stalks your plant, B7 is not a good option.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[SnTMan]

Well yeah, but about useless for the Original Problem...

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

 

[r6155]

All that you guys are talking about the strength of B7 or B7M is lost if torque (low accuracy method) is used to tighten the studs.

Regards

 

[Big BE]

@r6155, please tell me how the operating strength of a stud is affected by torqueing it vs tensioning.
The material still has the same properties regardless of tightening method. I don't disagree with the low accuracy comment but I would not agree that is really an issue for MOST applications.

 

[r6155]

@ Big BE
See ASME PCC-1, it is clear

Regards