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ELECTRO MAGNETIC INSPECTION (EMI) |
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| Arctic Pipe Inspection's Electromagnetic Inspection Unit (EMI) utilizes the finest and latest developments of electro-magnetic, gamma ray, and eddy current detection devices, combined with automation, to offer fast, sure and cost efficient pipe inspection. The pipe is subjected to five electronic inspection functions with just one pass through the unit. | |||||||||
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| Shown left is the electronics package for a typical EMI unit which will gather signals from the inspection unit (shown below) which is then displayed at the operators console (shown right) for evaluation. | |||||||||
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Plant 6000 EMI unit inspects tubes up to 13-7/8" in diameter |
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| PROCEDURE SCOPE This procedure covers the electro magnetic/gamma measurement inspections of ferromagnetic OCTG. This inspection also includes grade verification. All procedures will be in compliance with API Spec 5CT unless customer specified otherwise. EQUIPMENT Arctic Pipe Inspection, Inc. ROBCO V EMI unit consists of five separate inspection processes carried out simultaneously by an automated inspection unit: i.e., longitudinal, transverse, wall thickness, grade verification and demagnetization. In addition to prove up equipment covered in Section 11.0, a small hand-held moto-tool capable of cutting a notch not to exceed .040" in width will be used, as well as selection of hand tools to adjust unit. In circumstances where inspection is being performed for the manufacturer or processor and/or certain customer specifications apply, EDM notches on the inside and outside surfaces will be cut. It is Arctic Pipe Inspection, Inc. policy that notches will not exceed 2" in length or .040" in width in accordance with API 5CT. Many customers specify shorter lengths and thinner notches and these specifications shall over rule API 5CT and this revision of Arctic Pipe Inspection, Inc. procedure. Customer specifications shall be furnished prior to inspection start up in order for specifications to be adhered to. CALIBRATION The unit shall be calibrated on a test piece of same diameter, wall thickness, surface conditions as the material to be inspected. This standard may be a length of the material to be inspected. A minimum of one longitudinal and one transverse notch will be cut into the pipe OD in accordance with API Spec. 5CT Section 9. Wall thickness at this point will exceed or be nominal for that material. After completion of the job these notches will be removed by grinding and contoured to a smooth surface. Longitudinal and transverse detectors will be calibrated with a pulsar (longitudinal shall be pulsed using the notch) on each individual coil. All coils will be pulsed to the same reference standard through the unit in the 12, 3, 6, and 9 o'clock position. Unit shall pick up all notches in similar fashion. If the unit does not pick up these indications it will shut down until such time as repairs are made or unit is made capable of doing so. Gamma thickness measurement (chord and thru-wall for casing, thru-wall for tubing) will be calibrated with a standard of two known wall thicknesses, then unit will set on the reference pipe at point with known wall thickness 360° in the calibration area. A base line will be established representing nominal wall thickness and variations to this line will be proportional to the actual wall thickness variation. Once calibration is complete the operator may not adjust any electrical or mechanical settings which could affect the calibration. CALIBRATION FREQUENCY The unit shall be calibrated at the beginning of each job, after every 50 lengths, when the power is interrupted and at the end of the day. Calibration shall be run at the 12, 3, 6 and 9 o'clock position. GRADE COMPARATOR CALIBRATION The grade comparator utilizes eddy current balanced coil technique. The reference joint used to set the grade comparator must be identifiable as the proper grade for the material being inspected. If the grade of the material passing through the "inspecting" coil is different than the material in the "reference" coil, an audible alarm is sounded in the operator's compartment. Any material that sounds the audible alarm must be identified by hardness testing or other acceptable methods or the tube shall be removed from the string for rejection or further evaluation. If the grade cannot be established the tube will be rejected. INSPECTION TECHNIQUE After all calibration procedures have been satisfactorily completed, inspection may begin. Lengths will be passed through the unit via automatic rollers and into inspection heads. Any indication or discontinuity which exceeds the established reference level will be marked for further evaluation. Only supplementary requirements provided on the Arctic Pipe Inspection, Inc. Work Order may supersede the criteria for acceptance or rejection. The following conditions are cause for rejection: Quench cracks; Arc burns; Any area measured to have a wall thickness less than 87½ % of nominal wall thickness; Any imperfection or irregularity which meets or exceeds the specification to which the material is being inspected; Any imperfection or irregularity in the product which deems the piece to be uninspectable; Any piece or pieces that are not reasonably straight according to API 5CT or customer specifications; Any material which cannot be identified by mill stencil or grade verification cannot be established; Any indication found to be greater than the indication by the reference standard. If the imperfection should not exceed 12½ % of nominal wall thickness it shall be removed by acceptable methods and corrosion inhibitor shall be applied after remaining wall thickness has been verified. If the defect exceeds 12½ %, it may be removed if the remaining wall thickness does not fall below 87½ %. DEFECT REMOVAL AND VERIFICATION PROCEDURES Any discontinuity whose magnitude is greater than that allowed by any applicable specifications must be removed or the piece must be rejected. After a discontinuity has been removed, or in some instances partially removed, its removal or partial removal must be verified by the same inspection method which originally detected the indication or by any other inspection method deemed appropriate. The area from which a discontinuity has been removed must be contoured so that the structural integrity and the inspectability of the piece has not been significantly reduced. This specifically includes contour of all filings, grindings, and machining so as to remove any potential stress risers. After contouring it must be possible to make an ultrasonic wall thickness measurement for the remaining wall at the deepest portion of the exploration. All discontinuity removal is to be conducted by qualified personnel to insure that good materials are not scrapped or rejected and that complete removal and a subsequent re-inspection can be accurately performed. The area from which a discontinuity has been removed is to be coated with a protective coating to prohibit corrosion damage to the material surface. This coating is to be applied at a stage during the inspection process when it will not interfere with subsequent inspections and before corrosion damage has occurred to the unprotected surface of the piece of material being inspected. Any discontinuity located during the inspection process and determined not to be a rejected defect and also not to require removal is to be accurately evaluated as to its severity. The discontinuity depth and remaining wall, whichever is required by specification, in the area from which a discontinuity has been removed shall be accurately measured and documented. DEMAGNETIZATION Demagnetization is accomplished by reversing the polarity of the field induced by the transverse inspection system. This coil system demagnetizes the tube full length. The demagnetizing process takes place as the pipe is exiting the EMI unit. The first length inspected through the EMI unit will have the residual magnetization check with a field intensity meter. Amperage will be adjusted by the variac to the DC coil to produce an acceptable limit of residual magnetism. Twenty-five Gauss or less is acceptable. Gauss level shall be checked at the beginning of each shift, at least every 4 hours throughout the shift and at the end of each shift. |
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