Carbon steel bolts HDG used for 316SS flanges 1

[17092003]

Hi,

Can anyone provide some assistance to the following:

Limitations in specifying ASTM A193 2H/A194 Gr. 2H bolts and nuts HDG in piping material classes 316SS dual certified ANSI 150 up to and including ANSI 900 DN 1/2" to DN 24".
Piping material classes in 316SS material dual certified have been specified for corrosion properties. Minimum design temperature for all 316SS piping material classes is (minus) - 29°C.

Thanks

 

[Ripz]

You stated your bolt spec incorretly.

It is somewhat common to use CS bolts in SS piping, even with the potential for galvanic corrosion. Usually, they'll specify the use of Galvanized or Tropicalized CS bolts.

 

[CoryPad]

The limitations include galvanic corrosion of the bolts (which requires knowledge of the application environment), bolt fracture due to thermal expansion differences (which requires knowledge of temperatures throughout the system and elastic modulus and thermal expansion coefficients for the different materials), loss of clamping and leak risk due to yielding (see thermal variation above), and attack of stainless from zinc (requires high temperature).

 

[moltenmetal]

We limit the use of galvanized or zinc-plated B7/2H fasteners to below 400 F. Zinc isn't protective beyond 400 F, and well above 400 F you have the risk of zinc liquid metal embrittlement of the stainless flanges and potentially of the fasteners too. From 400 to 800 F we use black oxide or plain oiled finish. That's also true of pipe shoes/hangers etc.