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[MW:24017] Exchanger Bolting SA 540 B23 Cl1 vs B24 Cl1 for low temp service

By Materials & Welding

We are having U type exchanger with  Shell side MOC –SA 516 Gr 70  and Tube side MOC-Titanium2

Design code is ASME Sect VIII Div.2 Ed.2013

Girth flange Bolting for shell side specified as per FEED is SA 540 B24 Cl. 1 ( size is 3")

MDMT of Tube side and Shell side is -46 °C

 

 

However, due to regret letter received from fasteners manufacturers,Vendor  proposed to use SA 540 B23 Cl.1

 

The proposed MOC may be acceptable by designer since :

1.       Due to NO change in allowable stress, design of Girth flange will not change.

2.       Since these fasteners are externally coated with robust painting system before installation, slightly low % of Mo content can be taken care of.   

 

However, main concern is the Impact Testing requirement :

 

1.       B24 : Minimum energy values are shown in Note 3 of Table 2 of SA 540

2.       B23 :  Note 4 of Table 2 of SA 540 states that "No minimum values established and tests shall be run for information only".

3.       How to check these values are minimum required/acceptable for -46 deg.cel ?

 

Considering, MDMT of exchanger as -46 deg.cel, can it be allowed use SA 540 B23 Cl.1 ?

 

Request your views on same.

 

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