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