First question - Is the pressure higher than 15 psig? or whatever is the cut off for tank vs pressure vessel. If it is then it's a Pressure vessel and needs to be designed to Pressure vessel codes. If it's not then a variety of shop built tanks can be used - just find a sutiable vendor.
90C though is a high temperature and if this water leaks out is harmful to humans and also needs thermal protection to stop people touching it and getting burnt. So you can't just buy any old tank and expect it to work.
That's in your hands, not anyone else's.
But even if it's more than atmospheric (even 1-2 psig), it means you're really into a circular vessel type tank rather than a simple square tanks.
this is a very poorly written question.
Please provide further details and what exactly your question is.
NB: ET is a forum for asking questions, it's not a free design service.
Remember - More details = better answers
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