Considering Corrosion Allowance in flange thickness 2

[Amr Shams]

A closed drain drum having a 2" nozzle with blind flange RF.
Should I use the UG-34 calculations and include the corrosion allowance of the vessel to the flange thickness? or use the typical standard blind flange with a suitable rating without considering corrosion allowance?
we already purchased the standard flanges without considering C.A. But the AI said that All permanent blinds shall be designed in corroded condition.
If adding the corrosion allowance is mandatory what are our options to solve this issue?

 

[SnTMan]

Amr Shams, if you can't convince your AI that CA need not be applied, then it seems a UG-34 approach (or other, depending on your Code of construction) is your best option.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[LittleInch]

This post has something simialr

https://www.eng-tips.com/viewthread.cfm?qid=482280

Be very careful about calculating B 16.5 flanges to ASME VIII. They usually fail.

I would say that a standard flange is fine and just allow for the thickness to be checked on aa regular basis and if it approaches the 3mm RF, then replace it.

If the AI won't see sense then you might need to buy special blind flanges made a bit thicker.

But these are standard components so shouldn't need to be design checked and as said usually fail when you do, even without any corrosion....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Christine74]

Pretty sure your AI is wrong on this. There is no mention of "corrosion allowance" anywhere in ASME B16.5, so presumably some amount of corrosion is built into the B16.5 pressure/temperature ratings.

If you had an unusually high corrosion allowance like 6 mm/0.25 inches you might consider running UG-34 calculations just to confirm, but otherwise it's completely unnecessary. There are literally millions of ASME B16.5 blinds currently operating in place with no calculations done to account for the corrosion allowance.


-Christine

 

[LittleInch]

Plus it is very easy to check the thickness and replace if you really really want to.

Or just coat it.

Or get one made from Duplex.

Anything other than having to do a calculation

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[david339933]

I see this both ways.

Standard Designation: BPV Section VIII Div 1
Edition/Addenda:
Para./Fig./Table No:
Subject Description: Section VIII, Division 1 (1995 Edition, 1995 Addenda); UG-44(a) and (i)
Date Issued: 05/29/1998
Record Number: BC96-534
Interpretation Number : VIII-1-98-28
Question(s) and Reply(ies):
Question: In Section VIII, Division 1, must corrosion allowance, if specified, be considered when providing flanges and flanged fittings per UG-44(a) and UG-44(i)?

Reply: Yes.

You must also list the covers and bolting/nuts in the remarks of the data report, per W-2.

That being said, you can have different corrosion allowances for different parts of the vessel.

Standard Designation: BPV Section VIII Div 1
Edition/Addenda:
Para./Fig./Table No:
Subject Description: Section VIII, Division 1 (1998 Edition, 2000 Addenda); UG-45
Date Issued: 08/07/2001
Record Number: BC01-589
Interpretation Number : VIII-1-01-81
Question(s) and Reply(ies):

Question: When the nozzle has a different corrosion allowance than the shell (or head) it attaches to, shall the shell (or head) corrosion allowance be used in applying UG-45(b)(1) and UG-45(b)(2) in Section VIII, Division 1, and the nozzle corrosion allowance be used in applying UG-45(a), and UG-45(b)(4)?

Reply: Yes.

 

[r6155]

Measure actual blind flange thickness and verify with UT every year.

Regards.

 

[LittleInch]

Just paint or coat the bloody thing with a two pack epoxy and tell the AI it won't corrode....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

No paint of any type should be considered as a permanent protection. When paint is applied to the inside of a
vessel, corrosion allowance should be added to the wall thickness of the vessel as if it were unprotected. It is a good practice.

Regards

 

[LittleInch]

I was being a little sarcastic....

But you can brush on coatings which would work.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

Or weld overlay.

Regards

 

[bcd]

Can you just cut a solid round gasket from sheet which will completely block the media from touching the blind flange?

 

[SnTMan]

That might be he most practical thing, if the AI buys it.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[GD2]

Amr Sarma,

1) You can’t use standard B16.5 flange when CA is required. Flanges under B16.5 and B16.47 are without CA
2) for the same material, B16.5 allowable stresses are usually higher than sec Viii Div 1 allowable stress.

The above two conditions will give you a thinner flange you want to use in Sec Viii.

Even if Sec Viii allows use of B16.5 flanges, the AI had stopped it coz there is CA involved.

GDD
Canada

 

[SnTMan]

B16.5 flanges are used in PV work with CA applied all the time. Usually nobody kicks about it.

EDIT: Extensive experience has shown CA of even 1/4 in is no problem.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[GD2]

Amr Sarma,

One easy option you can try is:
Do the actual thickness measurement of the blind flange and see if you will be lucky to get a positive tolerance close to CA. This might convince the smart ass AI.

GDD
Canada

 

[LittleInch]

GDD,

I don't agree with your statement.

CA is part of pipe wall thickness so is part of the flange thickness.

The particular issue here is a blind flange thickness. Most people think the AI is being rather OTT.

Blind flange are not "designed" which is where the issue lies I think.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

See (OP).... "But the AI said that All permanent blinds shall be designed in corroded condition".

Blind flange IS NOT PERMANENT.

Regards

 

[LittleInch]

Hmmm, I'm assuming that there is a nozzle, a flange and a blind flange, i.e. take the blind flange off and all the contents of the pressure vessel come out.

Unless and until you replace the blind flange with another flange and a pipe or a valve or something, then its part of the vessel.

Could be there it's entire life or one month - who knows?

However there is an argument to say that it can be very easily replaced if it is shown to be "corroded". Problem is B16.5 doesn't actually specify if there is a CA or not included in the thickness of a blind flange and the AI is being very pedantic in asking for one.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GD2]

LittleInch,
I simply bet on the blind flange thickness tolerance (+3.2/-0.00 mm) for the 2 inch flange on the following pretext:
Say it’s a 2 in x 150# BF.

With no CA requirement:
Nominal Thk= 19.1 mm
Min thk: 19.1 mm ( zero tolerance)
Max Thk: 19.1 + 3.2= 22.3 mm ( +3.2 tolerance).
A inspector will accept the flange that will come with at least 19.1 mm.

Now assume the CA is 3.2 mm and the flange measured thickness is 22.3 mm.
Can this flange be accepted? I would say yes. Is it not the same thing as receiving the flange with min tolerance?

A logic to outsmart the AI.

GDD
Canada