Jackwill,
Steam is 5.5 bar manometric, this is 6.5 bar absolute, from vapor tables the temperature is 162.1ºC (approximate).
If you are in design please take in count the “Dow Chemical Company suggest use of the fluid in the temperature range between 450º-750ºF” (232.2º-398.9ºC) (Geiringer P., Handbook of Heat Transfer Media, p. 77).
From your MLDT, the mean temperature of Dowtherm A is approximately 83.5ºC, from table V-4.3 Geiringer handbook, the viscosity is 2.1 cP --> Heavy hydrocarbon.
From Wuithier P., Raffinage et Génie Chimique, Vol . II, p. 1067, in French, for “Réchauffeurs” -->Vapeur d´eau (steam) and Hydrocarbures lourds (heavy hydrocarbon)--> U = 6-60 BTU/hr ft2 ºF. We can take Um = 66/2 = 33 BTU/hr ft2 ºF = 187,4 W/m2ºC. This value include fouling and pressure loss is between 0.35 to 0.7 kg/cm2.
Warning: Approximate overall heat transfer coefficient: Use as guide as to order of magnitude and not as limits to any value. Coefficients of actual equipment may be smaller or larger than the values listed (From Branan C., Rules of thumb for Chemical Engineers, Table 3 p. 33).
I Hope help you.
Napo.