THE ALTERNATING CURRENT FIELD （交流领域）.pdf

THE ALTERNATING CURRENT FIELD MEASUREMENT (ACFM) CRACK DETECTION AND SIZING TECHNIQUE AND ITS APPLICATION TO IN-SERVICE INSPECTION. A RAINE TECHNICAL SOFTWARE CONSULTANTS Ltd. INTRODUCTION The Alternating Current Field Measurement (ACFM) technique had been used primarily for the detection of fatigue cracks in offshore structures both on the subsea and topside structural sections. The inspection applications were then extended to the inspection of pressurised systems and process plant i.e. pressure vessels and pipe work. Evaluation trials have been carried out to prove the detection and sizing capabilities of the technique compared to the results obtained using more conventional techniques such as magnetic particle inspection, eddy current and ultrasonic creep wave. The technique was then used on the inspection of non-magnetic materials such as stainless steel and titanium and proved equally successful. Since then ACFM has played a useful role in the inspection for non-fatigue cracks at normal and elevated temperatures. Procedures have been produced so that transverse defects can be differentiated from longitudinal defects and cracks detected on the inner surface from the outer surface can be easily identified (only on certain materials and within a specific thickness range). THE ALTERNATING CURRENT FIELD MEASUREMENT (ACFM) TECHNIQUE The ACFM technique is an electromagnetic non-contacting technique which has been developed to be able to detect and size surface breaking defects in a range of different materials and through coatings of varying thickness. The basis of the technique is that an alternating