9 replies to this topic

[chem2013]

Hi Everyone,
 
I am facing this following situation:
 
MAWP calculation guideline:
 
This needs to be calculated for process vessel for hot and corroding condition.
 
Now one exchanger manufacturer is avoiding MAWP calculation for plate and frame exchanger by stating that calculation is not possible for gasket sealing system. Therefore, MAWP for plate and frame exchanger is considered to be same as design pressure of exchanger following note 34 in ASME Sec VIII, Div. 1 ,2010.
 
I understand ASME Sec VIII, Div. 1 does not indicate gasket MAWP calculation requirement explicitly.Therefore, manufacturer should calculate MAWP for exchanger plate only. I assume no other component will have lower MAWP than plates.
 
Kindly advice whether exchanger manufacturer is correct or manufacturer should calculate MAWP for plates as per guideline.
 
Looking for your advice.
 
Regards.
 

[Pilesar]

A single exchanger plate is not a pressure vessel. I agree with the exchanger manufacturer that design pressure is the maximum allowable working pressure of plate and frame exchangers. The gaskets are the weak point. Welding the plates together overcomes the gasket problem, but then the plates cannot be separated. If the manufacturer states MAWP as if the gasketed exchanger were a welded plate exchanger, what good would that do? The gaskets would still fail first and the exchanger could never be operated or pressure tested at the imaginary MAWP.

[fallah]

chem2013,

 

Attached code case of ASME may help you out for your query...

Attached Files

•  ASME Code Case 2766.pdf   49.56KB   138 downloads

[chem2013]

Hi Fallah,

 

The conclusion from this case is not clear to me. Point (a) talks about calculation of MAWP for all pressure parts. So, my understanding is manufacturer still needs to calculate MAWP for all necessary pressure containing parts. For gasketed plate portion no test or design calculation is required if remaining conditions particularly ( and (d) are met.

 

So, in summary, MAWP of plate and other pressure containing parts to be calculated as per code. For,gasket part no test or design calculations are necessary if remaining conditions are met.

 

Please share your opinion.

 

Also kindly share where this case was published like any journal etc.

 

Regards.

[fallah]

chem2013,

 

Actually i think determination of MAWP for plate heat exchangers that contain gasketed plate packs is generally performed by proof testing or design calculation; and the code case 2766 introduces the pre requisite requirements to do so without performing proof testing or design calculation but without referring to the detail of such determination...

[Art Montemayor]

This is an interesting and necessary topic that can be misinterpreted if not viewed from the practical point of operations.  I agree with both Pilesar and Fallah because they bring up some very important points that could mitigate a serious event.

 

There is some basic information from the OP that needs to be clarified.  The need for identifying the MAWP of a pressure vessel – and this plate & frame exchanger could be interpreted as a pressure vessel – is typically for identifying the safe set point of a possibly required PSV.  If, in fact, the unit can be subjected to over-pressure, this is necessary to know.  Pilesar’s comments correctly point to the practical and potential hazard in any gasketed equipment: the weakest point is usually the gasket.

 

The OP mentions a hot and corroding condition.  This makes the application a potentially hazardous and safety issue and makes Pilesar’s concerns and comments even more important in the event a PSV is required.

 

ASME code case 2766, as pointed out by Fallah, is meant to state that MAWP calculations are not needed for the plates and general construction as such.  However, as Fallah indicates, calculations and pressure testing are still viable in order to identify the EFFECTIVE MAWP.  What I believe is of importance here is that the unit will fail at the gasketed joint (as expected) and that pressure limit has to be identified – either by calculation and/or test pressure.  This, in my opinion is what is necessary to determine what the safe setting value of a PSV should be in order to protect the operating personnel that would be exposed to the hot and corroding fluid released through a failed gasketed joint due to over-pressure.

 

I believe the MAWP that the plate & frame supplier is alluding to is the MAWP of the metal construction and NOT of the total, operating unit.  Personnel have to be protected from the weakest part of the unit – the gasket – and not necessarily from the rest of the equipment because it is the gasket that will fail first – not the unit per se.  This can be verified by a test pressure.

[Neelakantan]

the design pressure and testing pressure is always vexing with regards to PHEs. I remember a case where we procured a set  of PHE from Alfa LAVAL for use in FPSO.  it was clear at the time of purchase that the test pressure shall be 10% over the max actual operating pressure and not based on the design pressure of the line components.

 

Just before towing from the yard, the client wanted the ABS to have CE classification (as per PED) as the client wanted to move the FPSO to Europe after three years of service in Indian ocean. ABS had a review session and PED classification document was generated for all the pressure vessels. the PHEs were not considered as Pressure vessels for CE certification on the ground that PHEs are field assembled (actually our design has three cases of having different exchanger area and the number of plates)

 

Standard manufacturers like AL normally give a test pressure  based on the type of the gasket and torque value of the bolts after re-assembly..

 

regards

neelakantan

[Rezachajang]

ASME Code Case 2766 is a good reference for ignoring MAWP calculation for plate and gasket but in most of project specifications accepting Code Cases depends on Client's approval.

In this situation if Client didn't approve, MAWP shall be calculated with Proof test or design calculation (ASME Sec VIII Div 2 or ANSYS Finite element Analysis) 

But I couldn't find any sample of MAWP calculation for PHE manufacturers so I think Clients must accept based on manufacturers standard and specifications.

[lyeskrt]

We have a media filter for water treatment ,the design pressure is 10.0bar and the operating pressure is 8.0bar .I would like to know the setting of its PSV.

[fallah]

Hi,

 

It's supposed you mean barg for pressure units; then the relevant PSV set pressure should be 10 barg or lower...