Using higher permissible stress material instead of SB-151 O60 for floating head flange.

[mechengineer]

Hi Experts,
Floating head heat exchanger.
Shell side medium: see water.
Shell side DP at DT: 26.3 bat at 150 deg.C
Shell side DP at DT: 17.2 bar at 70 deg.C
Shell ID: 450 mm
Floating falnge material: SB-283 C70620.
Client data sheet for the bolt material: UNS C70620.
Vendor uses the bolt material of SB-151 O 60 for the floating head flange. The bolt size will be 2.5" (63.5 mm). It is too large.
May anyone advise a higher permissible stress bolt material applicable to instead of SB-151 O 60.

Regards

 

[CuMo]

Sometimes clients might assign bolting material identical to the main components which isn't always the best solution,
simply because they don't know better.
Have you checked if it is possible to use "more" standard bolting materials instead?
This bolting is quite exotic and will be too expensive for sea water.