Flange corrosion allowance on bore 1

[BigTank]

I'm wondering if anyone else noticed this, and if anyone can straighten out my logic if need be.

Examining the Compress calcs for an integral ring-type flange shows that the BORE corrosion allowance is applied in several places as if this corrosion allowance were not for the bore dimension but for the radial thickness dimension (as is the case for a shell [thickness]).

Re-stated: if the vessel shell corrosion allowance is 1/16", then the corrosion allowance on the bore dimension of that shell would be 1/8".

It appears that in Compress this BORE corrosion allowance is being treated as if it were the shell corrosion allowance (applied to a radial thickness). For example, Compress uses the BORE corrosion allowance on the shell thickness g0 for a ring-type integral flange calculation, thus actually applying twice the desired corrosion allowance.

Similar application is seen in calculating hD, hT, HD, and the factor h0.

This seems incorrect. Am I correct that this is incorrect, or do I need corrected?

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[vesselfab]

in calcs....CA should be 1/16" everywhere

yes bore will go out an 1/8" larger...1/16" on each side

 

[BigTank]

Precisely, vesselfab. But Compress is doubling the 1/16, calling it correctly by the 'bore corrosion allowance' moniker, but applying this now doubled CA to one shell thickness when used as an integral hub to a flange.

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[vesselfab]

hmmm

my compress does not do this

have you got the 1/16" ca as a global ca and calling out for another 1/16" in nozzle calcs?

 

[BigTank]

i guess my point is that, when editing the flange in the model, there is a box for 'corrosion bore'. in that box is the 1/8 as determined per discussion above, but it's taking the undertoleranced pipe used for the shell as the integral flange hub, and deducting 1/8. i wish i could upload some screenshots and/or a portion of the calcs to show you.

that is, if i enter the corrosion allowance in the appropriate box for a given model component, any global setting should be overridden for that component.

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[BigTank]

in addition, it seems to be applying this thicker corrosion allowance on its own whim throughout the calcs. perhaps i should email the model to Tom...

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[vesselfab]

the corrosion on bore is 1/16"

not 1/8


go to set options

nozzles 2 tab

click on set corrosion allowance same as parent

 

[BigTank]

but my problem is with body flanges, not nozzles.

my ca on the tab you mention is set to 0. the 1/8 came into the flanges automatically.

something else i should mention is that this particular model in which i discovered the problem is an exchanger.

nevertheless, 'ca bore' implies a ca applied to the bore dimension whereas, in the radial direction, the code applies the ca to one vessel thickness, not both across the cross-section. either Compress has a misidentification of the ca in the flange component windows (which seems most likely), or the calcs aren't using it correctly. at least that seems to be the obvious problem...i'm just looking for confirmation or denial.

man i wish i could upload some files! IT is pretty tight here...

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[BigTank]

so did we come to a consensus?

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[BigTank]

okay. over the past 8 work hours i've answered my own question:

it appears that the label in Compress for this particular corrosion allowance parameter is misleading, especially when considered in conjunction with the automatic input of corrosion allowance into the flanges from the heat exchanger input. for example, if i enter heat exchanger information with a corrosion allowance of 1/16" shell-side, all of the shell-side body flanges will have their 'corrosion allowance bore' parameters automatically populated with 1/8", leading one to believe that this automatically populated value is applied to the bore DIMENSION. but the reality of the calculations is that the value in the 'c.a. bore' box is applied through the calcs "per-side" so-to-speak (only to the thickness dimension not the bore dimension as implied).

i hope my headache helps someone else along the way. i can't be the only one that noticed this.



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