Shell-tube type heat exchangers are often used to exchange heat between a high-pressure fluid and a
low-pressure fluid, and the pressure difference between the two fluids could be significantly high. If the
difference in the design pressure between the low-pressure (LP) and high-pressure sides is greater than
that covered by American Petroleum Institute (API 520 and 521) 10/13th rule, dynamic analysis is
required to ascertain that the maximum surge pressure that could be reached does not compromise the
integrity of the LP side of the exchanger. API guidelines also notes that attention should also be given not
only to the shell-side of the heat exchanger under evaluation, but also to the “upstream and downstream
systems” This paper offers further insight into the importance of including the surrounding piping systems
around the subject heat-exchanger where a tube-rupture scenario is considered, and also directs
attention to the importance of correctly specifying the appropriate boundary conditions (B.C.) at the far
ends of both the upstream and downstream piping systems. It demonstrates the effects of specifying
different B.C. on the maximum pressure surge via a case study of a hot separator vapour condenser in a
bitumen hydrotreating unit, where the process fluid on the tube-side is a vapoureliquid mixture at
9660 kPa(g). The vapour mass fraction of the process fluid is approximately 0.5, and is mostly hydrogen.
The fluid on the LP side is cooling water connected to the plant supply and return cooling systems as well
as another adjacent low pressure condenser. The design pressure for the cooling water piping system and
the adjacent condenser is 1380 kPa(g).