Criteria for choosing between Breech lock Type heat exchanger and D(TEMA) type heat exchanger

[Chengin]

Hi,
I'm a project engineer working for a revamping project in a refinery.

In our company, there are several RDS process unit, which processes under about 200bar.
I found that some heat exchangers in RDS unit are breech lock type, which built 20years ago.
But some heat exchangers in other RDS unit built last year are D(modified D) type.

I think D type is better with respect of maintenance and price, because it doesn't need diaphram plate.
So I wonder what type of heat exchanger people choose these days when in comes to high pressure.(Design pressure is about 200bar)
Also I would like to know if there is any criteria for choosing breech lock type heat exchanger.

Thank you.

 

[SnTMan]

JJINY, TEMA D (Special High Pressure Closure) is a kind of all-encompassing term, that would include diaphragm designs, breech-lock and other special designs. The common feature of these is some way to reduce the required bolting as compared to, say, an Appendix 2 design where the bolting must both restrain the hydrostatic end force and maintain a gasket seal.

A diaphragm design uses a welded seal such that the bolting is only required to resist the hydrostatic end force. They are straight forward and pretty much anybody can design and build one. Breech-locks tend to be more or less proprietary designs, so some fabricators do them, some don't. They typically seal with a gasket, but would use separate bolting or other means to seat the gasket and resist the hydrostatic end force

Not sure, but the design shown appears to be a diaphragm, as the channel cover is beveled back, this normally would provide access to seal weld the diaphragm. The internal structure appears to be a "pass box", which has more to do with isolating the channel cover and it's seal from a relatively large temperature differential than pressure as such. I've not seen one exactly like it (if that's what it is), looks like some kind of liner in the channel? Some kind of removable split ring?

Breech lock does have the advantage of not needing a welded seal so might be the choice for ease of maintenance, diaphragm design should be relatively less expensive and possibly more reliable.

Regards,

Mike

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

 

[Chengin]

Thanks for reply
The drawing I attached is Modified D Type, which has diaphragm gasket.
So it welds to channel part(seal weld).

 

[SnTMan]

Another thing about the pass box that did not occur to me in my previous post: It is needed to seal the tubeside passes one from the other, so that the normal sealing of the pass plates against the channel cover via gasket ribs is not needed. Regardless of temperature differentials.

I feel better now

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