Monoblock isolation joint or isolation gasket plus sleeved bolts?
Monoblock isolation joint or isolation gasket plus sleeved bolts?
(OP)
Electrical engineer straying a little outside his field of expertise so bear with me. 
I've received a TQ regarding the type of isolation joints we would prefer to install on the pipework on a liquified gas storage facility. I'm familiar with the old-fashioned type of joint using an isolation gasket and sleeved bolts and have used this in an operational environment on cooling water service in a power plant environment without any difficulty other than inadvertent connections across the joint by instrument impulse lines, valve actuator cable armour, and the like. The pro's and cons of each type of joint in hydrocarbon service is new to me. The process fluid is propane and pressure is up to approx. 40 BarG. Process pipework sizes are in the 200mm - 600mm range, possibly including some small-bore lines too.
Can anyone offer any insight or references which would be the more suitable isolation method in this instance, and why?
I've received a TQ regarding the type of isolation joints we would prefer to install on the pipework on a liquified gas storage facility. I'm familiar with the old-fashioned type of joint using an isolation gasket and sleeved bolts and have used this in an operational environment on cooling water service in a power plant environment without any difficulty other than inadvertent connections across the joint by instrument impulse lines, valve actuator cable armour, and the like. The pro's and cons of each type of joint in hydrocarbon service is new to me. The process fluid is propane and pressure is up to approx. 40 BarG. Process pipework sizes are in the 200mm - 600mm range, possibly including some small-bore lines too.
Can anyone offer any insight or references which would be the more suitable isolation method in this instance, and why?





RE: Monoblock isolation joint or isolation gasket plus sleeved bolts?
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RE: Monoblock isolation joint or isolation gasket plus sleeved bolts?
http://www.eng-tips.com/threadminder.cfm?pid=1529
Use translation assistance for Engineers forum
Note the rules include No Student posting
RE: Monoblock isolation joint or isolation gasket plus sleeved bolts?
1) Eliminate a flanged joint which is notmally the pipeline side of the ESD / isolation valve
2) Have far higher relaibility in terms of voltage breakdown and lack of galvanic corrosion onthe bolts
3) No crevice corrosion
4) Virtually as storng as the main pipe in torsion, and bending
5) Valid for all presures and temperatures
If the process fluid can transmit electrical current you need to be careful to internally coat the pipeline side to avoid internal corrosion, but that would also affect a flanged joint
The real key is item 1 for most operators as a leak int he flange on the pipeline side of your islation valve is very bad news
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Monoblock isolation joint or isolation gasket plus sleeved bolts?
I'm not certain but my understanding is that vessels are likely to be alloy steel and pipework will be stainless. Fluid is liquified propane and will normally be at or slightly above ambient temperature although from memory the design window is fairly wide from approx +60°C to -40°C. The vessels and pipework in question form part of a mounded storage facility which is in FEED at present.
LittleInch,
Thanks for the list, that seems to weigh fairly heavily in favour of the monoblock. I assume cost is significantly higher for the monoblock, but are there any technical disadvantages? I agree that minimising the probability of leaks is our number one objective, closely followed by minimising corrosion problems.
Should have stated before that it's an impressed current system and likely to be a fairly powerful one based on the initial estimates of required current from the piping guys.
RE: Monoblock isolation joint or isolation gasket plus sleeved bolts?
I hope you got the current requirements from the corrosion engineer, not the piping man... High current on a new system is not good, but doesn't mean high voltage all the time.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Monoblock isolation joint or isolation gasket plus sleeved bolts?
Longevity will be a big plus from my perspective.