The following thermal problems are caused by changes in pressure:
- With gas, the Joule Thompson effect may give sub zero temperatures (or cryogenic temperatures) due to high pressure drop across valves during startup (e.g. over production choke valves). During shutdown of a well, the upper part of the well tubing, will cool down rapidly because the ambient formation temperature is near to the seawater temperature, the tubing is normally not thermally insulated and the tubing is gas filled. This can give the following problems:
- Low temperature material problems
- Hydrate and/or ice formation
- High required hydrate inhibitor injection rate
- Required hydrate inhibitor injection rate above injection capacity
- For liquid and high pressure gas, the Joule-Thompson effect may give increased temperature (Joule-Thomson inversion temperature), which may be problem if there are high temperature design temperature problems.
- During depressurization, severe cooling may be caused by isentropic expansion (lost expansion work for the fluid at the entrance of the pipe which "pushes" i.e. does work on the fluid downstream, due to expansion ) in addition to the Joule-Thompson cooling. This may give temperatures below minimum design.
Joule-Thompson Cooling White Paper