Det Norske Veritas - Germanischer Lloyd

DNVGL  PIPELINE SUBSEA REPAIR
 N DNV-RP-F113

Annotation

Introduction

This Recommended Practice (RP) applies to fittings used for repair and tie in of submarine pipelines. These fittings include: Couplings, Clamps, T-branch connections and Isolation Plugs. Mechanical means connect these fittings to the pipeline, however, sleeves/couplings and T-branches may also be welded.

The section on the strength of the mechanical attachments is also applicable to pipeline recovery tools.

Refer to Figure 1-1 for typical fitting applications.

Couplings connect pipes by direct attachment to the pipe walls via mechanical or welded joints. Flange connectors differ from mechanical couplings as flanges join pipes via thick, machined pieces of additional material that is welded or forged to the pipe ends prior to installation.

Clamps are fitted externally to the pipeline to prevent leaks or add strength.

Hot-tap T-branch connections are fitted externally to the pipeline assembly even during operation. A pressurized pipeline would be machined open to allow fluid flow through the branch.

Pipeline isolation plugs are pumped with the pipeline fluid to the repair site and then activated in order to form an isolating barrier that can resist differential pressure.

The pipe itself represents the key member of the repair assembly with consequential limitations such as, but not limited to, pipe wall strength, surface irregularities, and deviations in shape. Fittings for subsea repair must be installed with caution to reduce the likelihood of damage, (e.g. seal damage).