Well you have to be more specific. Superheated or Saturated steam, English units or SI units. PI has the steam tables build into it.
You can calculate the Enthalphy of superheater steam by using the following in a dataset or calculated tag
StmSI_HPT('pressure','temperature')
pressure should be in kPa & temperature should be in celcius)
It will return J/g which is the same as kJ/kg or MJ/ton. Read your PI Server applications guide, it has a whole chapter dedicated to this.
