vent and drain removable closure

[pipe15]

this question is with respect to the use of flanges or threaded caps for the removable closure on vent, drain and test connections. all lines in question are either 1 or 2". Allowance for any threading would obviously be considered in pipe wall thickness. Jurisdiction is all ASME Section III or B31.1.

are there design pressure/temp limits where I must use flanges for closure or can I use threaded caps in all cases. downstream piping of all shutoff valves for these lines meet the design conditions of the different process lines.

thanks
Mark

 

[jte]

Mark-

I would suggest that you go to the field and have someone install a cap on a 2" threaded connection. Let it rust for 3 years. Now go back and try to remove it. Should be fun to watch… I can't claim to be the strongest guy out there, but I've had to call in help from my refinery technician neighbor in breaking an old galvanized steel 3/4" threaded joint. He's pulling on his wrench as hard as he can on one side while I'm backing him up with a wrench on the other side of the joint. We finally managed to break the joint open on the third or so try.

So, consider the abuse the joints will take and the torques applied to the system by a couple of gorillas trying to break the joint. Are you overstressing your 1" pipe farther down (maybe where it connects with a larger but thinner pipe?) with the load applied by someone trying to get the cap off? Figure a 250# guy hanging on a 24" pipe wrench to determine your moment.

Thus, acting as the owner's engineer, I would veto a 2" threaded cap and question a cap on a 1" fitting. Flanges are much easier to open… For what its worth, I'm used to seeing plugs, not caps. Don't know why…

jt

 

[4everlearning]

Pipe15:
Go with the caps. Typical install.
JT's point is valid. Problem is, you either get beat up by whoever is paying for the higher cost of flanges, or the guy muscling the cap - pick your poison.

 

[pipe15]

thanks for your thoughts, but the bigger question is are there design conditions where I must use a flange set for closure?

thanks

 

[NozzleTwister]

For vents and drains, I'm used to seeing threaded forged plugs screwed into the end of the vent or drain valve. Also, the vents and drains I see are normally about 3/4"

For the Piping Spec that you have, I would use the normal valve specified for your line size and provide whatever closure is appropriate on the end of that valve.

NozzleTwister
Houston, Texas

 

[dcasto]

I've taken the position to never install all these drains and vents and design in ways to commision or decommision lines without them. Sometimes you are stuck, but the babysitting of 3/4" valves under LDARS is not worth their installation to begin with. You need to make the change.

 

[BigInch]

Use a plug, except if you have to attach some other piece of pipe or hose with flanges on them from time to time.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[pipe15]

so, if I hear you guys right, threaded closure is the way to go.

even if I have an ASME Section III Class 1, CL2500 rated system, with a Class 1 drain using a single 1" valve, I can still use a threaded cap for the removable closure.

I have had some people tell me that there is no way I can use a threaded cap in this case and that I have to use a flange set for closure.

thanks again for your thoughts
Mark

 

[BigInch]

Sorry... I meant that only for the <= 1" vents, drains and test connections. 1.5" and above ,for any type of connection, flanges appear to be preferred in most all cases.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com