Using Manways as Nozzles 2

[david6245]

Hello, I am a cheme and have what seems to be a dumb mechanical question.

In general, is the design of manways such that they are the same thing as nozzles? If I have a 24"-300# RFWN std wt manway, what is the difference between that and a 24"-300# RFWN std wt nozzle? Can a manway support the same load as a nozzle from a pipe?

I am wanting to re-purpose a decommisioned tower and the 24" manway would be a perfect nozzle for my process.

Thank you in advance,

David

 

[roca]

Yes a manway is the same as a nozzle with respect to pressure design and nozzle reinforcement design.
However for nozzle loads additional reinforcement pad thickness and / or pad diameter or additional local shell or head thickness may be required dependent on the required nozzle loads.
You need to get a PV engineer to check the current manway design details – in the corroded or as inspected condition (thickness checks) - and apply the proposed nozzle loads to see if it all works

 

[bernoullies123]

A manway and a nozzle are both branch connections. Manways are generally not design to sustain any external loadings as with the process nozzles.
The manway could be used as a process nozzle but the it would need to be checked with the anticipated piping loads at the connection.
Manways access is a requirement, so you will need to ensure that sufficient access is still applicable.

 

[EngAddict]

No, they are not necessarily the same. The thickness required for a manway or inspection opening may be reduced from that of a nozzle, irrespective of any additional nozzle loads. Check the code to which it was designed and get a copy of the mechanical design report to check.

 

[keon2001]

check also UG-45....the thickness required for manway and nozzle might be different....

 

[torsani]

I think if you want to use a manway as a nozzle, it should be in accordance with UG-45 rules for nozzle.

 

[eadwine]

Just one practical consideration, Manways are installed on vessels in specific locations for specific internal maintenance operations. If you convert the manway into a process nozzle, what happens to the Maintenance Dep't's/Contractor's ability to access vessel internals for maintenance and repair?

Better to install a new nozzle on the vessel under the applicable code.

 

[jte]

David-

The manway cover is a part of the vessel. Removing it permanently should be treated as an alteration - you are changing something which is listed on the U-1 form by removing the blind and converting the manway to an access nozzle.

As keon pointed out, the minimum thickness requirements for nozzles are a tad different from those for manways. However, chances are that you have a Sch 60 or thicker manway and this won't be an issue.

Adding the loads from a 24" pipe may be an issue. The area reinforcement required by code for nozzle openings is only marginally related to the reinforcement which may be required for piping loads. The nozzle needs to be checked by a vessel engineer for this. Are you planning on adding pipe supports as well? New pipe on an existing support? Are the loads from the new pipe less than or equal to those for which the support was originally designed. These need to be checked, but are probably not a killer for your project.

The manway access must be maintined, as eadwine pointed out. This may be accomplished by using a removable spool piece on the piping. Keep in mind that the piece will have to be rigged in and out every time the process/access opening is used [ref: VIII-1 UG-46(f)(7)]. Make sure there is rigging access for a crane or a permanent structure to move the spool piece. Add a lifting lug to the spool piece at its center of mass to assist in rigging.

jt

 

[unclesyd]

We have multiple SS vessels where the manway is used for process also. These are mostly where we use the 20" or 24" nozzle on the vessel as the connection for a vertical calanderia to the column. Originally we used a "tee" type connection with a cover plate that allowed access to the top of the tubes and as a manway entrance to the column. In a very corrosive area we eliminated the cover plate and started using an elbow type connection, which required removal for egress to the column. When we used cover plates they were routinely flipped or changed out.