Safety Instrumented Systems on Older Facilities - An Approach for Addressing SIL-Requirements in Relation to Minor and Major Modifications

Abstract

This thesis presents a new approach for SIL management during modifications on existing SIS. This approach is in formof a working procedure that can be followed during SIS modifications. The procedure provides a comprehensive guidance on carrying out partial modifications on existing SIS in light of SIL requirements stated in relevant regulator and standards. The reason for establishing the new approach is that the Oil & Gas industry has been facing challenges on how to account for SIL requirements on existing SIS after Petroleum Safety Authority (PSA) Norway has started to require guideline NOG 070 (NOG-070 (2004)) to be used for the activities related to SIS on the offshore installations. In this thesis, by existing SIS it means SIS that were buidt before the new requirements from PSA were released (2003). The main challenge associated with SISmodifications is how to treat the existing part of the SIS.

According to the framework guideline §24 (PSA (2013a)), technical operation regulation §70 (PSA (2013c)), the SIL requirements related to existing SIS only apply when there are physical changes in the existing SIS and are only applied to the parts that are being modified. For the existing SIS part, a simple SIS follow up activity is recommended such as collecting failure records and identifying different failure modes in order to gain an overview of the reliability performance of the existing components.

The new approach established in this thesis is based regulatory recommendations, requirements and guidance provided by standards. The guidance found for handling modification in different industries in literature survey is also fundamental for the development of this approach. A case study is presented based on a modification project executed by Aker Solutions MMO. It also illustrates how the new approach can be applied in a SIS modification example. The approach is based on the working procedure for SIS in Aker Solution MMO. However, it is applicable for other suppliers as well as operators.