South Stream Deepwater Pipeline System: A Case for Waiving the Hydrotest

Abstract

The traditional scope of pre-commissioning for a pipeline system includes filling the pipeline with liquid (typically water) and pressure testing to confirm the integrity and leak-tightness of the system. This methodology is described in almost all design codes, and typically represents an important criterion for the acceptance of the completed system by the owner / operator. As the industry takes on offshore pipeline systems in deeper and deeper water, the relevance of this traditional approach has come into question. Specifically, it is not clear that the benefit of hydrotesting a deepwater pipeline system outweighs the costs, risks and potential environmental impact. For this reason DNV introduced the possibility of ‘waiving’ (= omitting) the hydrotest in OS-F101, its offshore standard for submarine pipeline design. In order to waive the system hydrotest, OS-F101 demands that specific, additional conditions be satisfied to ensure that the overall level of safety is maintained. To date, only two smaller pipeline projects have received such a hydrotest waiver. The South Stream Offshore Pipeline project, which is presently approaching its implementation phase, will be the third. South Stream comprises four 32-inch diameter pipelines each with a length of approximately 930 km and traversing water depths up to 2,200m. The South Stream project is re-defining the state-of-the-art in offshore pipelines. Due to the extreme water depth, harsh seabed and large internal volume of the South Stream lines, traditional hydrostatic testing would not be the most environmentally friendly and risk averse solution to ensure pipeline integrity and safety. This paper will present the main requirements and associated solutions for the South Stream pipelines in order to obtain a DNV OS-F101 hydrotest waiver, including: • Review of the benefits and challenges for deepwater pipeline hydrotest • Discussion of the DNV OS-F101 waiver requirements • Implementation of the waiver requirements on South Stream