# OHTC of fully buried pipe

Overall heat transfer coefficient (OHTC) of the buried pipe.

In offshore developments pipeline burial may be required for protection and on-bottom stability by means of placement of rock, grit or seabed material on the pipe. Acc. to a publication from Bai2005, burial can result from the gradual infill of sediments on a trenched pipeline; it can also develop from seabed mobility or pipeline movement.

When a pipe is fully buried a term, $h_{soil}$, is added to the definition of the overall heat transfer coefficient to account for the heat transfer by conduction through the asymmetric soil layer surrounding the pipe. The outside film coefficient $h_{ext}$ is replaced with a pseudo film coefficient, $h_{amb}$, modeling the heat transfer by convection at the sea/soil interface.

Case when $D_{ext}/2$ < $H$.

Symbol
$U_{buried}$
Unit
W/(K.m$^2$)
Formulae
 $\frac{1}{\frac{D_{ref}}{D_{in} h_{in}}+\frac{D_{ref}}{D_{wall} U_{wall}}+\frac{1}{h_{buried}}}$ Carslaw & Jaeger $\frac{1}{\frac{1}{h_{buried}}+\frac{1}{h_{amb}}}$ Morud & Simonsen / OTC 23033 $\frac{1}{\frac{D_{ref}}{D_{in} h_{in}}+\frac{D_{ref}}{D_{wall} U_{wall}}+\frac{1}{h_{buried}}+\frac{1}{h_{amb}}}$ Ovuworie $\frac{1}{\frac{D_{ref}}{D_{in} h_{in}}+\frac{D_{ref}}{D_{wall} U_{wall}}+\frac{D_{ref}}{D_{ext} h_{soil}}+\frac{1}{h_{amb}}}$ fully buried
Related
$D_{ext}$
$D_{in}$
$D_{ref}$
$D_{wall}$
$h_{amb}$
$h_{buried}$
$h_{in}$
$h_{soil}$
$U_{wall}$
OHTC of pipe wall [W/(K.m$^2$)]
Used in
$U_{OHTC}$