PED - classification problem

[IvekG]

Hi to everybody,
I need help from experienced engineers regarding classification of equipment according to PED.
In my firm we usually manufacture small hot water air heaters for use in industrial environment. Now we have an inquiry for steam heat exchanger that will be used for heating air that is used later in some process.
Heat exchanger is made of steel finned tubes and steel headers. Tubes are welded to tubesheet on top of which is half-pipe header (I think it is called bonnet header) also welded.
Steam is 2,2 bar; 170degC; connection is flange - DN80
Air is heated from 20degC to 100degC.

My question is:
Is this heat exchanger considered as piping (acc. to article 2.3 of PED) or is it considered as pressure vessel?

I think that it is pressure vessel, but I am not sure and the engineer in certification agency was not very helpful.

I hope my case is clearly explained. In case more information is needed please do tell.
Thank you.

 

[XL83NL]

Normally, it's considered a vessel, such that you need to determine the overall volume to do the classification. However, the exception which may be applicable here is guideline B-04, which provides an escape and allows classification of the HE as piping, under 3 conditions;
[ul]
[li]air is the secondary fluid,[/li]
[li]they are used in refrigeration systems, in air conditioning systems or in heat pumps,[/li]
[li]the piping aspects are predominant.[/li]
[/ul]
Review B-04 of the PED guidelines completely here.

If you have further doubts, please feel free to post your question, or contact your notified body and explain them in detail your plan, so they can help you further.

 

[XL83NL]

Hi Ivek,

I see you have logged in onto the website a day after I posted my reply. I see you are a new member with only 1 topic (so far). So far so good. Please take this the good way, but it's good practice that when someone replies to a query that has been posted, and puts his or her effort into given a professional opinion or statement of facts, that this is appreciated by the OP in some way or another. Just a simple thanks can already be enough. Im not 100% sure if you have alreayd read my reply, I'm just assuming; if Im mistaken, then Im sorry.

Regards

 

[dbday]

Hi,
Further to this PED classification problem.

Can I modify the question slightly.

If I have a bare vessel with nothing inside, and say an internal volume of 50 litres.
I can obviously work out the classification for the pressure using the Pressure multiplied by Volume rule etc.

However, what happens if my vessel has some solid metallic internals of some description that take up a significant proportion of the internal volume.
Lets say they take up 50% of the volume, so lots of internal pipes, solid bulkheads, etc etc.

What happens then to the classification then, do I still use the original 50 litres, or can I mark it down ?

Thank you in advance for any views on this.

 

[XL83NL]

No, the internal volume decreases, however there are 2 situations;
- the internals are just 'plain' metallic materials, like support plates, buble tray, fixtures, etc. Items which contain no differential pressure. For this situation, their volume can be subtracted from the overall volume.
- when you have an internal pipe, which conatins pressure, 'running' through a vessel (typically like the situation with a heat exchanger, or coolingcoils), you now have 2 pressure volumes, or chambers, and need to split the assessment. Thus, do the assessment twice, one assessment for each volume or chamber. The specific properties (like fluid type, etc) of each chamber have to be taken into account for each assessment.

 

[dbday]

Hi XL,
Gee, that sounds complicated, but helpful to my situation.

My actual bar volume value for my empty vessel comes out at 51.
Considering air and designing as a pressure vessel, it seems to me that this is just above the boundary PSV=50 where moves from SEP to Cat 1.
Group 2 gases for vessel.
So obviously I want to find a reasonable justification to put it into SEP.

As my internals are substantial solid metallic rings holding perforated tubes between them it sounds like I can subtract the volume of the rings, but not the perforated tubes.
Would that be your understanding ?

 

[XL83NL]

Yes, provided the tubes dont hold any pressure and are open to the internal atmosphere of the vessel. Can you provide a sketch?

 

[dbday]

Hi XL,
See attached sketch.
The unit is cylindrical in shape.
It has pipe caps for ends (not flat as drawn) with couplings to connect.
The internals rings are solid.
The dashed line represents a perforated cylinder.
I hope it is clear.
Thanks

 

[XL83NL]

Yes, in that case, subtract the volume of all internals.

However, if, for some reason, there's a case where the user of this device could, under certain circumstances, remove some internals and hence increase the volume of the pressure chamber, I think this needs to be accounted for in the classification. This could only be the case when the internals are not permanently affixed to the isnide, e.g. by screws. But that's an exceptional case which is very infrequently found, in my experience.

 

[dbday]

Hi XL,
The internals are welded in position, so detachment should not be a problem.
Thank you for the help.

 

[XL83NL]

You're welcome.