Acoustek™ Pipeline blockage detection system—case study

iNPIPE PRODUCTS™ was approached by a North Sea Operator who required assistance with validating their Gas Import / Export SSIV [Subsea Isolation Valve] closes within 60 seconds and meets their pipelines Performance Standard document.

The SSIV forms part of the ESD [Emergency Shut Down] System on the pipeline and as such is classified as safety critical equipment and is subject to regular testing to meet the criteria set out in the Performance Standard document. The SSIV was situated subsea at the base of the riser in 136m water depth and is around 338m along the pipeline length. The SSIV acts as a secondary isolation against hydrocarbon release in an emergency event, but the valve has no position indication feedback to DCS [Distributed Control Systems] meaning an accurate closure time cannot be confirmed by closing the valve alone. Prior to utilsing Acoustek™ gas gun equipment, the closure time has been inferred from hydraulic feedback, but this method does not confirm the status of the closed valve nor closure time without the requirement of venting the riser. Venting the gas from the pipeline riser is a costly option and a process that brings its own set of risks to the platform operator, platform, and environment.

Following a review of the project details and discussions with the Client, iNPIPE PRODUCTS™ mobilised a Field Engineer to visit the site with iNPIPE PRODUCTS™ Acoustek™ gas gun equipment, all of which can be deployed within 24 hours in emergency.

The Acoustek™ gas gun uses acoustic reflectometry to detect blockages or partial blockages in gas pipelines. In essence, an acoustic pulse is generated by a small pressure pulse generated in the gas column. This pulse travels along the pipeline and as it passes locations where there is a change in acoustic impedance it generates a reflection, which then travels back along the pipeline to the injection point, where it is detected and recorded.

Table 1 Pipeline details

The Acoustek™ connection point selected was a 2” instrument tapping located topsides.

Table 2 - Pipeline details (* Distance from connection point)

This scope of work was conducted by the iNPIPE PRODUCTS™ Field Engineer, supported by the Control Room, Area Authority and was completed within a single shift. The acoustic data was processed by aligning each shot and as the ‘Timed’ case was identical to the ‘Closed’ case, the valve is confirmed as closed by the time the pulse reaches it in the timed case. This transit time is <1 second, indicating that the valve is closed at 41 seconds (worst case) after the command was issued. If the valve was still partially open at this point, one would see a reflection at lower amplitude than the fully closed case and therefore a conclusion can be made with absolute confidence that the SSIV meets HSE guidelines. Figure 6 provides corroboration of the technique, showing a reflection consistently detected in the ‘Open’ case at approximately 31.5 seconds. The initial pulse being at 1.5 seconds, this corresponds to a feature at 30 seconds round trip time. Based on the speed-of-sound this will be at a distance of approximately 5.4 km, consistent with the distance to the Receiving platform.

Figure 1 - Acoustek Shots - SSIV Closed

Figure 2 - Acoustek Shots - SSIV Open

Figure 3 - Acoustek Shots 40 Seconds After 'Close' Command

Figure 4 - Comparison of Shots

Figure 5 - Detail Comparison at 1st Echo

Figure 6 - Open Detail