Method of installing an in-line structure in a pipeline

Abstract

A method of installing an In-Line Structure (ILS) to a fluid-filled pipeline extending from a reel, over an aligner, and through a lay-tower during offshore reeling, the pipeline having an oblique part from the reel to the aligner, and a vertical part from the aligner through the lay-tower, including at least the steps of: (a) draining fluid in the fluid-filled pipeline from the vertical part of the pipeline to create a drained portion of the vertical part of the pipeline up to and around the aligner; (b) cutting the pipeline at or near the draining of step (a) to create upper and lower open ends of the pipeline; (c) installing the In-Line Structure to at least the upper open end of the pipeline; (d) locating a vent hose through a vent port in the In-Line Structure; (e) adding fluid into the drained portion of the pipeline and venting air from the drained portion of the pipeline through the vent hose to wholly or substantially fill the drained portion of the pipeline with the fluid.

Description

[0001]The present invention generally relates to methods of installing an In-Line Structure in a fluid-filled pipeline extending over a reel on a vessel during offshore reeling, particularly but not exclusively a pipeline having an internal liner. In particular, the methods can be part of averting the wrinkling of an internal liner of the pipeline due to bending during offshore reeling. The invention finds particular utility in the laying of Mechanically Lined (rigid steel) Pipeline (MLP) from a pipelaying vessel.BACKGROUND TO THE INVENTION[0002]In the reel-lay method of laying an offshore pipeline, the pipeline is provided from a reel or spool on a vessel, towards a lay-tower designed to direct the pipeline down through the lay-tower and through a moonpool in the vessel and into the sea for laying. The lay-tower may be in a ‘vertical’ position relative to the general plane of the vessel, or at an angle thereto, generally by rotation of the lay-tower at or near a point on the vessel...

AI Technical Summary

Benefits of technology

The patent describes a method for rejoining an offshore pipeline that has been cut during construction or maintenance. The method involves using an In-Line Structure (ILS) to re-install the cut section of the pipeline. This allows for the continued laying of the pipeline and offshore reeling of the cut section, either simultaneously or at a different time and location. The technical effect of this method is to improve the efficiency and reliability of offshore pipeline construction and maintenance.

Problems solved by technology

Pipelines for use in the subsea conveying of fluids such as gas or crude oil are often exposed to the corrosive effects of these fluids which, unless the pipeline is protected by some material resistant to their effect or corrosion, can cause damage to the pipeline and even pipeline failure, which is difficult and expensive to remedy.

While a Mechanically Lined Pipeline (MLP) may be preferable from a pipeline manufacturing and cost-effectiveness perspective, a known problem is that, in pipeline construction methodologies that involve reeling the pipeline onto and off a storage spool during production and laying, forces imparted on the pipeline during the reeling process by bending of the pipeline can cause the internal liner to wrinkle.

In reeling a Mechanically Lined Pipeline (MLP), significant bending strain is imparted to the pipeline as it is wound onto and unwound from a storage reel which can result in a significant amount of wrinkling in the Corrosion Resistant Alloy (CRA) liner.

This wrinkling is an undesirable result, as the wrinkles can cause mechanical and material issues with the liner (such as embrittlement), as well as causing significant problems within the pipeline during and after the pipeline is commissioned and is in use, which can lead to the failure of the pipeline before the end of its serviceable term.

Given that the cost per unit weight of Corrosion Resistant Alloy (CRA) and other liner materials can be very high, the cost of the liner material can become a significant component of the fixed material costs of the pipeline.

Thus while using a sufficiently thick liner can reduce wrinkling, it can also lead to the use of a large amount of an expensive liner material.

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