"Our system is simpler," says Caffyn. "When we set out to develop Penguins via a subsea tieback, we believed we could install a pipeline rated to 400 bar, which is the closed-in tubing-head pressure of the wells. But as we got more into the design of the pipeline, we found two problems. The first was the sheer thickness of the steel - the 16-in. pipe would have been very thick indeed. It was not certain which pipe mills in the world, if any, could supply the pipe to the specification required. The second problem was the design of the pipe-in-pipe system itself. It soon became clear that the stresses would be too large to allow the surface S-lay option to work, and the upheaval buckling stresses would have made trenching and burying a very expensive exercise with an uncertain outcome. We therefore looked at an instrumented protection system. Our design philosophy is that, although the line is rated for lower pressure than the pressure of the wells when closed in, the line is also designed not to burst at that tubing-head pressure. It would possibly deform radially, but it wouldn't rupture, avoiding a hydrocarbon release. That determined the level of valve instrumentation required at the manifolds. For Penguins, we have called it an 'Instrumented Over-Pressure Protection System,' rather than the more widely recognized 'High Integrity Pressure Protection System.' Our philosophy has been developed in close consultation with the UK Health & Safety Executive, which has accepted our proposal for this project."