OHTC of part of pipe in contact with water

Overall heat transfer coefficient (OHTC) of the wetted exposed part of the pipe.

It is equal to the OHTC of an unburied pipe comprises three primary terms modeling the heat transfer by convection at the inner surface of the pipe wall in contact with the pipeline product (gas, oil, water, and possibly solids), the heat transfer by conduction through the pipe wall layers, and the heat transfer by convection at the outer surface of the pipe wall in contact with the ambient fluid. For cables, the first term is missing.

Case when $D_{ext}/2

Symbol
$U_{exposed}$
Unit
W/(K.m$^2$)
Formulae
$\frac{1}{\frac{D_{ref}}{D_{wall} U_{wall}} + \frac{D_{ref}}{D_{in} h_{in}} + \frac{D_{ref}}{D_{ext} h_{ext}}}$
Related
$D_{ext}$
$h_{ext}$
$U_{wall}$
OHTC of pipe wall [W/(K.m$^2$)]
Used in
$U_{OHTC}$
$U_{partially}$