Exploration • Drilling • Field Services
High performance ropes for riser tensioner systems
Dr Roland Konrad discusses wireline tensioner systems and the effects of different rope designs on the safety and cost-effectiveness of riser tensioner systems.
R
iser tensioner systems constitute critical components on offshore platforms and floating production storage and offloading vessels (FPSOs), as these systems compensate for the wave
motions of such vessels or platforms. Te most important requirements for steel wire
ropes used in Riser tensioners are high breaking strength as well as long service live under flexural stress, as safety requirements and cost-effectiveness are key criteria on offshore platforms. Meanwhile, eight-strand high performance ropes with plasticised cores and compacted strands are already being marketed by various manufacturers. Compared with six-strand ropes that are being widely used these days, eight-strand ropes offer advantages in terms of life span, safety and value.
Older riser tensioner systems rely on the so-called slip and cut method. In this case, the steel wire rope is wound in one large length onto a reel. Only a part of the length is used in the tensioning system. After a defined number of bending cycles the
steel wire rope is displaced by a defined length and shortened. Tis serves to ensure that the zone subjected to the highest continuous flexural stress gets shifted at regular intervals. In order to save space and reduce weight, newer systems no longer use the slip and cut method, but rely on steel wire ropes that are of a fixed length. It is especially in these new systems − but also in the slip and cut systems − that plasticised eight-strand rope designs such as Teufelberger’s QS 814 VG has their advantages. Eight-strand high performance ropes, compacted by using Superfill technology, feature superior minimum breaking loads as compared to conventional six-strand ropes of the same diameter. As a result, the specific loads individual wires are subjected to will be lower, and the safety factor of the riser tensioner system will increase accordingly. Te benefit of plasticised, lubricated ropes for riser tensioner systems is their enhanced durability obtained through the cushioning characteristics of
Fig. 2. QS 814 VG riser tensioner rope.
Fig. 1. Wireline riser tensioner system.
Te reason for recent developments regarding eight-strand high performance ropes in this segment is that riser tensioner systems have undergone profound modifications, as will be explained below.
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