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Welding Neck Flange description ISO PN

Welding Neck Flange description ISO PN

Welding Neck Flange description ISO PN

Dear all,

I am working in an EPC company for refinery heater. I am now working on a revamping project for which I have an small issue.

We are going to manufacture a new furnace and it will replace the existing one. That means, the we are going to connect our furnace on the existing process line (done by flange).

On the plant drawings I have in my hands, it seems that flanges from client side is defined as ISO PN 100 DN 150 for example.

It seems that flange defined by ISO PN or only by PN are not exactly the same. I have to define the flange of my furnace and my main question is my flange will be EN or ASME Flange.

Does anyone know if ASME & EN flanges can be assembled together without any issue ? or should I respect ASME-ASME Flange or EN-EN Flange combination ?

For my case ISO PN is a demomination for ASME or EN Flange ?

Thank you in advance,

Best regards,


RE: Welding Neck Flange description ISO PN

EN 1092 flanges don’t mate with ASME B16.5 flanges. You need same to same. Also, ISO PN designation seems odd.

You haven’t stated the standard applicable here. ISO may mean anything, but ISO 7005 seems plausible. Either ISO 7005 or EN 1759 has both Class rated and PN rated flanges listed, if I’m not mistaken.

PN is by the way never related to ASME.

RE: Welding Neck Flange description ISO PN

From bitter experience, I recommend someone actually has a look at the flange and see what it is. Check what is stamped on the flange and measure it. If you are connected to an existing flange also consider site fit and if a site weld will be required.

RE: Welding Neck Flange description ISO PN

Well so far for such an important interface you have very little information if this is all there is.

You only appear to know the nominal size ( 150 or 6 inch) and the nominal pressure rating ( 100 bar) at some unknown temperature.

Your known unknowns include:
1) Actual specification that the flange was designed to ("ISO" is an organization, like "ASME" it is meaningless in technical terms without the added information)
2) The material of the flange
3) The derating of the flange at your operating temperature ~( depends on 1 and 2 above)
4) Bolting sizes and material
5) Confirmed dimensions and gasket type (RF, RTJ )

However you will need the same type flange. In general the different flange codes do not fit each other.

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

RE: Welding Neck Flange description ISO PN

Dear all,

THank you for all your helpful feedbacks.

I know that a lot of information is missing, but this is only what I have in my hands when I read the existing drawings dated on 1969...

The conclusion is that the flanges already on site are designed as per EN norm, but since the drawings might have been not in their last version, I will ask confirmation to the client.

Anyway thank you for your help and your time.

Have a nice day and weekend to everyone !


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