Elongation of LWN Flanges 1

[teokal]

Dear all,

I am facing a case where the existing LWN flanges (SA105) we have in our possession are shorter in length than those required by the new revision of the Pr. Vessel's drawing (they were ordered correctly as per IFC drawing). My question is wether we can elongate the LWN flange by welding a piece of SA106 GrB pipe of relevant thickness. Is it permitted by the Code (ASME BPVC Section VIII Div.1)? Is there a reference to it, either if it is allowed or restricted?
Thank you all.

Only best result in absolutely necessary time

 

[SnTMan]

teokal, as LWN flanges generally are made such that the ID is the nominal pipe diameter, it is not likely you will find pipe that matches ID or OD either one. Could it be done? Yes. Nasty? Very much so.

How did this change come about? If requested by the customer, see if they will pay for the change, or accept the deviation. If your mistake, eat it, or see if the customer will accept the deviation.

Regards,

MIke

 

[nickelkid]

A request for a deviation sounds very reasonable to me. When requesting be sure to have any associated cost and delivery impacts to the schedule. If the difference in length does not have any effect on the design other than minor changes in piping I would be surprised if they would absorb cost and delays. If it is on you, suck it up like SNTMan suggested and get the correct lengths.

 

[racookpe1978]

I disagree: The "pipe" portion of the longweld neck flange should be standard sizes, and should be acceptable for a full-penetration butt-weld joint on its length. The flange portion is made up to fit that pipe as indicated.

BUT! ... You need to look at reaction forces due to the extra length (greater moment arm, greater forces due to water hammer or relief valve opening, etc.) Also, you need to be sure the joints are not too close to the PV wall weld joint.

 

[gr2vessels]

My two cents! The pressure vessel calculations are only looking for the joint of the nozzle and the vessel wall. Accordingly, you need to provide sufficient nozzle neck thickness as per the code. The Code is not interested in the nozzle neck length, provided to have sufficient nozzle neck length for reinforcement.
Yes, you can extend the nozzle neck as you wish, provided it complies with the welding and material requirements. There is no other code restriction, hence the code stops at the weld of your extension to the LWN flange/forging. Remember, the PVC code stops at the first weld after the nozzle weld to the shell. Normally, the forged nozzle necks are tapered down the ST thickness just below the flange! The external nozzle loads are subject to piping loads and you need to negotiate the minimum loads with the piping designers or you can advise them of the load capacity of the nozzle as per WRC or similar/allowed calculations.

 

[SnTMan]

See the link:

http://www.lyncoflange.com/customer/lyflfi/customerpages/lwn_150_E.htm

 

[JStephen]

The pipe portion of a LWN flange is not normal pipe size, racooke. The ID will be the nominal size (4" is 4.000" ID). Pipe of similar wall thickness will be 4.5" OD with reduced diameter.