Subsea Pipeline Tie-in

Introduction

• The requirements of this subsection are applicable to tie-in operativons using welding or mechanical connectors. The operations can be performed onboard a laying vessel (in which case welding is the preferred method) or underwater.
•  Tie-in operations by means of hot or cold taps are subject to special consideration and agreement.
• Operating limit conditions with regard to the seastate, current and vessel movements shall be established. Uncertainty in weather forecast shall be considered.

Tie-in operations above water

1. The position of the tie-in shall be verified prior to start of operations. A survey shall be performed to establish that the location is free of obstructions and that the seabed conditions will permit the tie-in to be performed as specified.
2. Lifting and lowering of the pipeline sections shall be analysed to determine the critical parameters and operational criteria for the operation. Critical parameters/operational criteria shall be monitored continuously.
3. Lifting arrangements and equipment shall be designed taking into account the critical parameters and operational criteria for the operations.
4. The operation should be monitored to confirm correct configuration of the pipeline sections from the seabed and onto the vessel.
5. The alignment and position of the tie-in ends shall be within the specified tolerances before completing the tie-in.
6. Installation of mechanical connectors shall be performed in accordance with the Manufacturer’s procedure. For flanged connections hydraulic bolt tension equipment shall be used. During all handling, lifting and lowering into the final position, open flange faces shall be protected against mechanical damage.
7. A leak test to an internal pressure not less than the local incidental pressure should be performed for all mechanical connections.
8. Corrosion protection of the tie-in area shall be performed and inspected in accordance with accepted procedures.
9. After completion of the tie-in, a survey of the pipeline on both sides of the tie-in, and over a length sufficient to ensure that no damage has occurred, should be performed
10. It shall be verified that the position of the tie-in is within the target area prior to departure of the vessel from site. The pipeline stability shall be ensured and adequate protection of pipeline provided.
11. Requirements for dry welding are given in Appendix C.

Tie-in operations below water

1. In addition to the requirements in Subsection I200, the requirements below are valid for tie-in operations involving underwater activities.
2. Diving and underwater operations shall be performed in accordance with agreed procedures for normal and contingency situations covering applicable requirements.
3. Requirements for underwater hyperbaric dry welding are given in Appendix C.

ARTHIT Pipeline End Manifold Tie-In Spool Installation

Reference :
DNV OS F101
http://www.arv-offshore.com/trackrecord/2008/spoolinst1.html