Development and testing of an innovative construction method for TLP tendons - results of NDE system experimental tests

摘要

Agip has developed a Tension Leg Platform (TLP) concept (Figure 1) for very deep water, a distinctive feature of which is the offshore installation procedure that foresees the simultaneous construction and installation of the tendons at site, by welding the joints on-board the TLP. This attractive idea had to be proved feasible, therefore a project was launched with the aim of designing, manufacturing and testing the special equipment required to be able to perform, on-board the platform, a fast high-quality welding operation and the relevant quality inspection. The TLP tendon system is composed of 16 pipes, having a diameter of 20 inches, a thickness of one inch and made of X65 grade steel. The project, which was awarded funding by EC (OG 486/92), has been successfully concluded. In the experimental phase a full-scale prototype of the innovative system, to be used for the construction of tendons at sea, was subject to an extensive testing campaign to confirm the performance of the equipment and technologies applied for the automatic welding and the on-line inspection of the joint, such as the repeatability of the processes and the respect of the time schedule for the tendons' installation. An extensive experimental trial, carried out with the prototype of the non-destructive examination equipment, has confirmed the system's capability to perform inspection operations with the quality and in the time requested by the installation specification. The scheduled period to deploy each tendon section is 90 minutes. This requires that the joint welding and NDE single tasks have to be carried out in 20 minutes each, because the remaining 50 minutes are dedicated to the handling of the tendon section and eventually to the welding reparation or equipment maintenance.