pressure vessel with coating (hydrotest and curing)

[wydim]

Hello all,

I've got to quote the fabrication of a pressure vessel with a HALAR ECTFE coating.
According to coating manufacturer/installator, this coating is cured at 800°F.

I've read UG-99(k)(1) and (2) and I understand I can request an exemption (from the client) to perform an hydrotest prior to the coating and also exemption from leak test.
but what about the structural integrity of the welded joints and base metal at 800°F AFTER the curing at 800°F.

I don't need an PWHT (SA-240, ''thin'' material, 145 psig ), but what is the effect of this temperature on the atomic structure of the SS during operation of the tank. do I need special considerations for the calcs and design?

thank you !

 

[0707]

800ºF is far from the transformation structure of SA 240 so at that temperature metalurgicaly nothing happens, but the melting point of HALAR ECTFE is 464ºF what will happen to your coating?

 

[wydim]

0707, thank you for your response.

this is from an official letter by the supplier that does the coating :

HEAT CURE PROCESS-WARNING-CUSTOMERS RESPONSIBILITY.
Coating of Teflon® requires curing at temperatures in excess of 800F. In some instances,
such temperatures may result in distortion of part or related metal stress relief changes
during or after the process. XXXXXX inc. does not and cannot assume responsibility
for determination of physical properties of your parts. If you do not know whether your
parts will withstand 800F Fahrenheit, please verify before submitting them to XXXXXXXXX inc.​

 

[Dhurjati Sen]

What is the curing time?
What is the tolerance limit for the curing temperature? Could it go upto 850F ?

Answers to above would determine whether sensitization or weld decay would take place.

And do remember, the question that why this coating is being done is not yet been asked.

DHURJATI SEN
Kolkata, India