The static calculation of pipeline systems is of major importance for the safety and life time of the products. It is as well an essential tool to optimise the embedding conditions and to support the contractor at the job site. Whereas small pipes of diameters under 300 mm are often classified and installed in regard to stiffness classes, larger diameter need a careful calculation. An SN class 2, 4 or 8 classification according to ISO 9969 (just to mention a few possible classes) will not give an indication, if the product has the necessary safety reserves under a short term or long term proof.
The calculation standard use in Germany is the ATV A 127 and there are some software packages on the market, to enable a qualified engineer to do the static calculation proof for most embedding conditions. The long term proof is carried out for 50 years and the basic idea of the German Method is, that after this period under constant load there is still a minimum safety factor 2 available for the product.
Overdesign in ring stiffness is not just a waste of money, it will also result in disadvantages which may lower the safety of the project. The biggest strength of PP and PE is the flexibility, leading to a small and controlled deformation under load. Even under overload just the deformation will increase, however there will be not break and no leakage. Pipes which are far too stiff will react more than a rigid pipe than a flexible one. This will lead to less deformation, but at the same time the risk of breaks and leakages is a major problem.
Both, the saving of natural resources and the engineered design, are necessary to guarantee the quality of the product now and in 50 years.