The production of oil and gas at water depths of several thousand meters required sophisticated solutions. The prohibitive cost of equipment failure and maintenance of deep water assets has resulted in zero tolerance of failure. Under these conditions, only an advanced verification approach will add value.
Verification requires a systematic and independent examination of the various phases of a subsea development project. The objective is to determine that the component or system has sufficient integrity and design life. Given its critical importance, DNV recommends that the verification activity includes independent analysis as well as significant attendance during fabrication and installation. DNV's verification services cover the design phase as well as fabrication and installation.
Design
DNV has been heavily involved in several deepwater developments in the North Sea, the Gulf of Mexico and West Africa since the mid 1990s. Through these engagements DNV has learnt to identify crucial design aspects in a systematic manner. We provide independent analysis and document review to:
- Assess correct global load effects
- Evaluate the effects of vortex-induced vibrations
- Analyse the risk of riser collisions.
We look at functional requirements of subsea equipment foundations, carry out advanced independent soil/structure interaction analysis and assess well temperature expansion and well/soil interaction. We evaluate the key components of the subsea production system from a reliability and integrity point of view using the approach in DNV-OSS-306 Verification of Subsea Facilities.
Fabrication
In-depth knowledge about materials, welding and non-destructive testing is a must for proper verification of the fabrication activity. In addition, close interaction with the personnel that did the design review is essential to ensure that key design and operational assumptions are reflected in the fabrication process. We have a systematic approach to quality surveillance of:
- Downhole systems
- Subsea wellhead and tree system (including choke, tubing hanger and connection systems)
- Manifold, foundations and template
- Flowlines and risers (including dynamic umbilical risers)
- Subsea control umbilicals
- Subsea production control system
- Subsea processing system
- Well intervention/completion/workover system
- ROT intervention system.
Installation
During the installation and commissioning phase we support our customers by providing inspection services and marine warranty. Depending on risk level, DNV's attendance varies from an audit-based approach to full 24/7 site team attendance. The financial and technical consequences of an accident of occurence during offshore marine operations can be devastating. This fact alone necessitates a well-defined inspection and marine verification, scope, and recognised technical reference, competence and experience.