The Field Signature Method (FSM) conosion monitoring techniqu e is based on "Ohms" electrical resistance Law and allows non-intrusive metal loss measurements of pipes and vessels to be recorded over a wide range of temperatures. The FSM was developed for the offshore industry where it is predominantly used for monitoring subsea pipelines. The first commercial subsea FSM system was installed in the mid nineties. Application in the petroleum refining industry was initiated in 1999.
This paper describes the FSM technique and presents several case studies where the FSM system has been utilized in a petroleum refinery. These include a variety of unit locations, operating temperatures and degradation mechanisms. This approach to non-intrusive monitoring is advantageous as it covers a prescribed area rather than just a localized thickness monitoring location. Also, it is useful for situations where other techniques are either not possible or very practical, such as at elevated temperatures or where access is difficult. Experience will be shared that shows this technique as one that can be used to enhance a corrosion-monitoring program in a refinery.
The Field Signature Method (FSM) conosion monitoring technique is a relatively new technology for the inspection and monitoring of metallic pipes and vessels. CorrOcean developed the FSM for the offshore industry where it is predominantly used for monitoring subsea pipelines. The FSM system is a non-intrusive, internal conosion monitoring technique (external corrosion is prevented by properly applying insulation covering), which is designed to detect and quantify general metal loss or pitting due to corrosion or erosion. The FSM technique is useful for situations where other inspection techniques are either not possible or very practical, such as at elevated temperatures or where access is difficult. The FSM technology can be applied to any geometry or wall thickness and maintains a sensitivity of five parts per thousand of wall thickness for general corrosion in refinery applications.
The Humber Refinery has thirteen FSM systems. The first four systems were installed in 1999 with another system installed in 2000 and a further eight in 2001. Initial locations were selected to assess the techniques capability. These locations were selected where suspected degradation mechanism were located together with a variety of process unit, operating temperatures and process parameters. This paper describes four of these locations, which are treated as generic, as they demonstrate the advantages of the FSM technique. This paper also discusses the results obtained, the advantages and disadvantages of the technique and an assessment on its suitability for use in a refinery environment. This will illustrate the requirements of both the client and contractor to ensure the success of the system.
THE FSM PRINCIPLE and SYSTEM
The Field Signature Method (FSM) corrosion monitoring technique is based on "Ohms" electrical resistance Law and allows non-intrusive metal loss measurements of pipes and vessels. The technique is based on feeding a current through a selected section of the structure to be monitored and sensing the electric field pattern by measuring small potential differences set up on the surface. The first measurement (signature) is unique to the geometry of the object. When general or local corrosion occurs, the pattern of the electric field will change and can be compared with the signature. By proper interpretation of the changes in the potential differences, conclusions can be drawn regarding, for example, general wall thickness reduction or localised corrosion.
Figure 1 gives an illustration of the FSM p
