ABSTRACT

The installation of pipelines and exploitation of oil and gas fields In deep water requires to perform tie-ins during construction phase In addition damages might occur during the pipeline life This means that a new pipeline section needs to be laid again, or there might be the possibility to repair the damage

Considering that at the moment few pipeline transportation systems are laid in deep water, but some other new installations, regarding both transportation and production systems, are foreseen in the near future, technological developments in the fields of repair and tie-ins are mandatory for the green light to these new projects This paper will be focused in particular on the installation problems and will give different solutions related to the installation of mechanical connectors with particular reference to large diameter pipelines

Due to the slight tolerances between connectors and pipeline, the main problem for their installatio1ns to achieve a good alignment between the installation tool and the pipeline

Based on Snamprogetti experience, both theoretical and experimental results about several different alignment methods will be discussed and evaluated In this paper Deepwater offshore test for the installation of 20″ Nuovo Pignone mechanical connector will be also discussed

INTRODUCTION

Mechanical damages on pipelines can be repaired in different ways depending on the water depth at which they are laid

When In presence of a damage causing a minimal leakage and/or a light dent In a pipeline, a repair sleeve clamp can be adopted

In the other cases a spool piece of the pipeline has to be replaced

In shallow water two different ways can be adopted to connect the new spool piece to the pipeline (after having cut and removed the damaged spool), namely

  1. Welding,

  2. Mechanical connection

Both methods can be performed either underwater (diver assisted operations) or on surface (in this case the two cut sections have to be recovered on surface, and, after the repair, they have to be relaid) The welding method, when feasible, is always preferred, since the pipeline integrity is replaced in this way

In deep water, where no diver assisted operations can be performed, diverless mechanical connections can be suitable for local repair, Instead of relaying the pipeline up to water depth where hyperbaric welding IS possible, to have a cost effective solution The three fundamental components of a connection system are the following

  1. mechanical connectors (to be Installed on the cut sections of a pipeline),

  2. ball joints (to adjust any misalignment between the spool piece and the Installed mechanical connectors),

  3. spool piece with a telescopic joint (to replace the damaged pipeline section)

The configuration of a spool piece is a combination of the three aforesaid fundamental components The assembly will change depending on the selected intervention procedure The same type of components are usually used when performing the mechanical connection In a tie-in In this case both ball joint and telescopic joint are usually requested to adjust respectively angular and axial misalignments between the Inboard and the outboard hubs

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