New experiences in scour protection for offshore platforms and pipelines

A special problem of offshore technique is set by scouring at drilling and production platforms founded on the seabed. Scours can jeopardize severely the stability of structures and therefore this danger should be noticed for all offshore structures already in planning. This paper will describe scour protection systems for offshore platforms which have been applied at the research platform “Nordsee” and in special testing fields in the North-Sea which were observed by measuring and in technical view during a longterm period. Furthermore, it will be reported about development and proving of a new system on scale 1 : 1. By using this system web mats in contrary to the practice up to now are installed independently from depth without aid of divers at pre-destinated seabed points as platform foundations. By this report the present scientific findings of scour protection systems are mainly based on laboratory results gained by in situ-measurings and observations. The aim of the performed measuring was to determine the influence of scour protection design and formation on the local orbital steady flow condition on sediment movements and on pore water pressures in the area of these sedimentations; the measuring results allow it to draw conclusions in favour of the construction, the longterm behaviour and the applicability of these scour protection systems. The system mortar intruded nylon mats was used for the first time at the research platform “Nordsee” in extended sea depth as regular scour protection. The experiences obtained on this occasion and the measuring results up to the present are giving evidence of the efficiency, the adaptability to the unevenness of the seabed, the flexibility and longterm behaviour of the scour protection system. Based on the measuring results evidence is given concerning the forces activated by motion of the sea and a corresponding dimensioning recommendation for this system will be submitted. This state of knowledge and the further development of technology pre-destinate this scour protection system not only for protection of platform foundations but also for pipelines.