Using Natural Frequency Response Monitoring (NFRM) to Reduce Inspection Costs for Ageing North Sea Platforms

Event:
Offshore Europe
Date:
September 2017
Author:
E. Whiteley, P. Ward - 2H, B. Taylor - Pulse Structural Monitoring

The offshore industry is faced with a tough financial market, requiring innovative solutions in order to reduce costs and increase operational efficiency. This includes solutions to ensure that maintaining the structural integrity of North Sea platforms is achieved as cost-effectively as possible without increasing risk or compromising safety.

Regular general visual inspection of fixed platforms for structural damage, by ROV fly-by, is a commonly used technique. There are two main concerns with this technique. Firstly, these inspections are costly to perform and secondly, damage may occur shortly after a scheduled inspection and go undetected until the next inspection. Both of these concerns are addressed through real-time structural monitoring. This uses automation of frequency detection and signal processing in order to avoid equipment and personnel mobilisations and provide immediate notification of potential damage. Inspections can then be conducted only when required and targeted at a specific area of interest, resulting in a significant reduction in overall integrity management costs. A platform monitoring system can be used on both manned and unmanned platforms and can be installed during construction or retro-fitted to an older installation.

A platform monitoring system, also known as Natural Frequency Response Monitoring (NFRM), works by measuring the natural frequency response of the platform under wave loading. The structural failure of a member will alter the natural frequency of the platform and the monitoring system will detect the change and alert the Operator. Prior to implementing this technique a screening study of the change in platform response following damage to critical members is necessary in order to ensure that incidents will be reliably detected

This paper presents a case study of a NFRM screening study prior to installation of the system on a North Sea platform. The structural analysis used to confirm the suitability of the NFRM system and the method for specifying the monitoring system itself are described. An indicative cost of procuring and installing the NFRM system is also presented.

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