We were calculating vessel skirt expansion from a chart in older days.
Later, people started using the same in equation form:

avg skirt temp (deg C) = (t-tamb)* 83.6/(k* h/ sqrt(thk) + 15.5) + t amb
where t, tamb are in degc, k = 1 for firebrick insul & 1.6 for no insul & h & thk are skirt height & thickness (k*h/sqrt(thk) > 120 to have this expression as valid). I wish my mentors here to help with the units of h & thk - are both of these in mm?

regards,

sam