Tube sheet material deviation

[Rakesh2560]

Hi all ,

we are in process of procuring tube bundle for our Kettle type S & T heat exchanger the following are the design parameters
Shell side tube side
corrosion allowance 0.125 0.125
design temp F 415 / 41 MDMT 500 / 41 MDMT
deisgn pressure psig 75 / FV 425 / FV
Test pressure psig 112.4 637.3

tube Moc SA 213 TP 316L
tube sheet MOC SA 516 Gr 70 + A 240 Gr 316l
code ASME Sec8 Div 1
Type BKU
Tema R
tube to tubesheet joint rolled and welded

Now vendor is suggest material A266 Gr 4 for tube sheet with clading with justification that forging is better then plate material due to high thickness (tube sheet thickness is 6.46" or 164 mm with 10 mm clad) .Is this change justifiable ?
Need guidance in this regards,

 

[abhimech1991]

Rakesh2560,

offcourse forging material is always better than plate . But if your contract asks for SA-516 gr. 70, then you can provide SA-516 gr. 70. Code allows both materials for the tubesheet application.

 

[Rakesh2560]

Thanks abhimech for the reply can you please provide me a reference code where this material are listed also this is very old vessel so should I ask vendor to calculate the thickness with new material allowable stresses and what about weld joints will there be any change in tube to tubesheet joints?

 

[abhimech1991]

Pls refer UCS-23 of ASME sec VIII div-1

 

[Afox88]

The stress values for SA-266 are in Section II-D. It is very common for tubesheets above 5" to be made out of forgings such as SA-266 Gr 4, as plate really needs to be available for heat exchanger vendors to buy. Forgings, as being suggested by your vendor, can be made to any size. That is not to say that the plate is not out there, I am sure that it is, but the less common the material = the more costly the material.

On a side note, if your vendor is a ASME Code vendor, they are mandated to do the new thickness calculations based on whatever material that is chosen. Therefore, if they hypothetically determine that Code requires a thicker tubesheet, they are obligated under CODE to provide it and provide calculations to you showing that this tubesheet will pass.