What is base metal and what material is clad layer. if clad layer is of Inconel, no much worries. If clad layer is of SS again which grade ? if 321 or 347 than again no worries. if its L grade of SS, due to low range of carbon, carbaide formation is avoided at large extent. If it is normal SS grade, i.e. 304 or 316, then carbaide formation may take place.
Another way is to provide inert atmosphere (argon during heating, due to cost constraint Nitrogen can be used),
The best way is to qualify PQR with corrosion test with simulated pre / post Heating.
I am not sure Mr. Shashank want to know about just heating methods.
In case of PWHT of any clad its advisable to apply chalk paste to avoid discolorisation of clad material.
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-- On 30 October 2012 09:45, Hemant Solanki <shm8324@gmail.com> wrote:
I have gone through PWHT procedure followed by Vendor in one of our Project for cladded equipment. even though SS cladding is there vendor has kept holding temperature upto 620°C (as per CS base material requirement). whether sensitization phenomenon should look into this or not. Because at this much temperature SS cladding may get sensitize and its property may get inferior.As per UCL-34 cautionary note
Postweld heat treatment may be in the carbide-precipitation range for unstabilized austenitic chromium–nickel steels, as well as within the range where a sigma phase may form, and if used indiscriminately could result in material of inferior physical properties and inferior corrosion resistance, which ultimately could result in failure of the vessel.
Can any body tell how to take care in such situation ?--
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