Temporary pig launchers and receivers (PLRs) are used during installation of pipelines prior to tie-in for
- gauging pigs (checking against buckling)
- cleaning pigs
- pressure testing
- injecting gel.
PLRs can also be used as pull heads. The number of branches depends on how many pigs will be launched. The drive medium is usually water supplied through a hose from the installation vessel. Both launcher and receiver work subsea. Valves and hot stab are accessible from two sides opposite each other in case twisting of the pipeline occurs.