A New and Controlled Method for Conducting Magnetic Particle Inspections

ABSTRACT Several influencing factors affect the results of data gathered during magnetic particle inspections, especially underwater. A new technique which makes use of Magfoils eliminates many of these unwanted factors. This technique can be used as the primary system to find discontinuities in ferromagnetic materials or used to confirm defects found by other systems. An on-line computer is used in conjunction with Magfoils to bring new levels of quality control and analysis into magnetic particle inspections. Non photographic permanent magnetic images are recorded at the worksite. By reviewing these images it is possible to determine, for example, crack length, width, and depth (a new dimension), thus allowing almost instant decisions to be made with regard to repairs. To reduce the bulk of storing the magnetic images, they can be electronically scanned and turned into digitized data flies for retention or for transmission to another site for further analysis. This technique is directly applicable to above and below water inspections. When used below water it allows the diver or ROV to use the magnetic particle technique in a more controlled manner than has been possible before. INTRODUCTION Offshore oilfield structures in US territorial waters are regularly inspected in accordance with Minerals Management Service (MMS) regulations and the American Petroleum Institute (API) code of practice RP2A. Structural members are inspected for signs of exposure to overloading. One technique used to detect early failure or fatigue cracking is the use of magnetic particle inspection (MPI). This technique is used both above and below water. When underwater work is being considered a rule of thumb often used in the industry suggests that completing the same task underwater as compared to on land is approximately ten times more difficult. This fact, when combined with the many variable parameters, necessitates the use of highly trained personnel. However, doubts will still exist as to quality control at the underwater worksite. BACKGROUND INFORMATION UNDERWATER MPI SCENARIO On arrival at the worksite, the diver must first convince the supervisor that he is at the correct node or structural member. This is normally done by reference to his depth gauge, and where possible, visually viewing the adjacent structure. (For this scenario we will consider that MPI has to be completed on the weld and heat effected zone around a structural node.) In the majority of cases, marine growth, paint and other substances will have to be removed to allow the inspection to continue. It is extremely important that the correct cleaning technique be chosen as the wrong choice can lead to cracks being bridged or covered over, too much metal being removed, too shiny a finish, which results in unwanted reflections when flash photographs are taken to record results. Having been cleaned to an acceptable standard, the weld is usually identified by one of several techniques (tape measure laid beside weld and/or clock positions marked). This will allow future intervention to locate the same position from the photographic records showing the defect.