Pipelaying In 2,000 Feet Of Water
Authors: Silvestri A. 
Published: December 2007

The importance of continuously developing submarine pipe laying capabilities in increasingly difficult environments is evident, as the industry needs to rely on improved technology to be able to plan and to carry out such advanced projects as are required to transport to shore oil and gas produced from remote offshore fields. Submarine pipelines can also be considered as a means of international transport of gas alternative to traditional liquefaction/rig sophistication and NGL tankers, even if deep water crossing are involved.

In view of assessing realistically the present state of the art in this field and of identifying and anticipating future trends and prospective developments, it would be useful to consider the evolution of deep water pipelaying technology referring to the direct involvement of Saipem during the last few years.

Although pipelaying projects were undertaken from the fifties, it was only at the beginning of the seventies that pipelaying projects were required in more difficult environments and projects were required in more difficult environments and greater water depths, with the development of the northern North Sea offshore. Such was the case in 1971 with the Forties Field when BP planned to install a 32" line for a length of 165 km. in water depths of up to 130 mt. a project at that time unprecedented.

BP decided to carry out lay trials in real scale to establish without reserves the feasibility of the project and also to define procedures and specific techniques to be adopted during the procedures and specific techniques to be adopted during the actual construction. Saipem was entrusted with these trials carried out offshore Gaeta during the second half of 1972 using the derrick/lay barge Castoro 2.

The following operations were performed:–Laying of a length of the same pipe which was to be used for the Forties pipeline (O.D. 32", W.T. 19.2 MM)–Repair of the pipeline in the maximum water depth–Experimental investigation on pipeline buckling, on buckle propagation and on buckle arrestors–Gathering of data and validation of theoretical solutions and operational procedures. With the support of the trials' indications, the main line Forties Field was laid during two seasons (1973–74) by two contractors.

Saipem using the same barge used for the Gaeta trials, eventually laid 103 km of line (out of a total of 165 km) in spite of adverse weather conditions which caused a substantial amount of standby in both seasons.

The good result and the reduced number of accidents and mechanical failures evidence the validity of the preparatory efforts and of the adopted techniques. At the end of the 1974 season, it was possible to connect the two sections of main line laid by the two contractors, adopting a method which had never been attempted before in similar water depth and for such large diameters. The method, jointly patented by BP and Saipem, calls for thorough studies and for execution in strict compliance with the pre-establish procedures.

In these conditions the method has proved to be safe as well as economical since it did not require more than 2–3 days to complete.

In 1975 and 1976 again under contact with BP, Saipem continued to work on the Forties Field with the laying of flowlines and with the performance of several connections to the platform risers: another original solution, now jointly patented by BP and Saipem, was developed for flanged connection patented by BP and Saipem, was developed for flanged connection of lines to risers.

During the long North Sea commitment with BP, it has also become evident that a close cooperation between client and contractor is not only useful but necessary when work is to be performed on advanced projects. After the trials in Gaeta and during the operations on the Forties, further developments were made in 1974 with the Messina Strait crossing.

This time Snam intended to verify the practical feasibility of laying a pipeline in 360 mt. of water depth as compared to the maximum depths reached at that time, which did not exceed 150–160 mt.