Connections on Bulk Liquid Tanks 4

[PuffJr]

I have been catching grief for having threaded connections on bulk liquid tanks. The knock on them is that they can easily be broken (with which I agree), and that the breach will be difficult to remediate if a break occurs (which I consider less valid).

In my mind, the breakage risk is more a function of size (and the connections in question ARE small, 3/4" and 1"), than of joining technology. A flanged nozzle in this range is just as easily broken as a threaded fitting. Also, a broken fitting on a filled liquid tank is a challenge to repair in any case; what makes the difference if it is threaded or flanged?

Avoiding small connections will be difficult. The half couplings are meant to accept thermowells, pressure transmitters, and ball valves for sampling. All of these have inherently small process connections. In addition, half couplings are nice because they are short, making the shipping envelope smaller (most of my tanks are shop-fabbed), and allowing a little better penetration by thermowells and other devices.

I am considering ignoring the concern about threaded connections, and adopting a minimum pipe size to mitigate the breakage risk. Even then, many devices (sensors, transmitters) will neck down from the process connection, merely displacing the weak point. Perhaps there are governing codes, of which I am unaware. What is considered best practice?

 

[nickelkid]

What is in the tank?

What are the likely sources of excessive loading on the connections?

 

[PuffJr]

Tanks contain motor oil, or motor oil component fluids.

Anticipated excessive loading would be collision with fork truck, aerial platform, etc.

 

[Artisi]

Have you considered "guarding" the fitting so it cannot be knocked - seems a simple solution.

 

[PuffJr]

Yes, on some devices very near the floor, we have half-pipe guards welded to the tank shell. Of course, field welds cause warranty and code compliance (UL 142, API 650) problems...

 

[djack77494]

Though I don't really agree with the practice, I think it has gotten quite common to specify a minimum of 2" flanged nozzles for all connections. You can bolt a drilled blind flange to the nozzle for any smaller sized instruments you may want to attach. Some feel this is more robust than using half couplings and screwed connections. The strong pluses to this, in my opinion, are avoiding any possibility of striping the threads on a coupling, plus a lessening of the likelihood of leakage at the nozzle.

 

[BigInch]

I'm with djack, its what all of us I know are doing.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[PuffJr]

OK, then. While I am standardizing with best practice, what projection is recommended for flanged nozzles? I have been using 6", I think.

 

[Artisi]

While a short pipe stub / flange is streets ahead of a threaded fitting welded directly to a tank, it doesn't overcome the problem of a small and fragile attachment being knocked and the fitting broken, guarding is still required.

 

[BigInch]

I'd use a minimum of 2" Diameter sch 80 pup w/ WN flange and leave room for welding, bolting, cleaning and painting. One pipe diameter or so should be enough in most cases.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[PuffJr]

Why is WN preferable to SO in this case?

 

[BigInch]

I haven't used a SO in 34 years of this stuff. See the star on this thread378-209647.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[djack77494]

Time for me to return the favor and backup BigInch. SO flanges seem to be (are) a no-no for vessel nozzles. I believe that to be reasonable since you don't have access to the backside of the flange and you may not be effective in filling potential "cavities". WN flanges are definitely more robust. A bit of projection can be handy for access for tightening the flange bolts. Balance against the risk of nozzle damage during installation.

 

[MJCronin]

djack, et al..

My turn..

My experience has been:

- All major AE firms and large engineering company guidelines require a certain minimum size on tanks and pressure vessels (usually 1.5 or 2 inch, NPS). That minimum size connection is flanged, schedule 80 or greater and 4-6 inch projection.

- I have only encountered WN flanges on pressure vessels ( never API 650/620 tanks). I have seen SS and CS pressure vessels in modest pressure service with slip-ons. Pressure vessels with flanges rated at 300 Class and high go with WNs

- Threaded couplings are common on Horizontal axis, atmospheric tanks (UL142 type) where the nozzle is above the normal liquid level.

My opinion only

-MJC

 

[djack77494]

MJC,
I stand corrected regarding my comment about using WN flanges. I agree that they are typically a requirement for pressure vessels, but not necessarily for atmospheric tanks. Nonetheless, as we tend to move towards being ever more conservative in our designs, it seems to have become common on atmospheric tanks. (Maybe I work in an overly conservative company.) Also, I concur with your additional comment about schedule 80 thickness.

 

[BigInch]

Why djack ? The question was, "What is considered best practice?" and it came without any further qualification of atmo or pressure tanks, horizontal, vertical or whatever. For a "one size fits all x API620/50 & pressure tanks rule of thumb best practice", I'll stick with my "minimum of 2" Diameter sch 80 pup w/ WN flange" above. Exceptions, sure.. there must be 1000s of them. Hope we don't have to give a recommendation for all of them.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[djack77494]

OK. Seems I'm under attack from the left and the right. Yet we are all basically in agreement. I'd be fine with saying WN flanges are "best practice" and recognizing that there are situations where they are not typically used.

 

[BigInch]

Attaboy.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/