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    Discussion in 'The main mechanical design forum' started by hgtyu123, Feb 17, 2013.

    1. hgtyu123

      hgtyu123 New Member

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      I would like share a content about visual examination and testing that are done by quality control engineers and third party inspectors during manufacturing process of the industrial equipment.

      This content defines requirements for visual inspection that is carried out in third party inspection assignment. The visual inspection must be done based job specification and client requirement. The professional hired to be in charge of these controls Non-Destructive Testing, visual and dimensional will need to have sound knowledge & experience in the fabricating work and will be subjected to the testing of sight on a periodical basis.

      Surfaces can be classified in two types: smooth surfaces (which can be pipes, flanges, etc.) & rough surfaces (which are welds, rough forged parts, rough coating etc). Also, they can be in grounded, brushed, sand-blasted and machined conditions. The visual inspection must be done directly or by specialized tools appropriate for inspection surfaces.
      The area under inspection must have at least 600 mm distance from inspector eyes. The angle is necessary to be 30 degree. The inspection surface must have a condition that allow easy inspection and possible to detect visible defects like corrosion, cracks and scratches.
      When the area to be examined is a weld, a more stringent visual inspection is carried out in order to detect possible craters, undercuttings, slag inclusions etc.

      According to the national and international standards for visual examination, the factors for observation must be considered as below:

      Indications which are critical: These indications that are found by the TPI inspector and vendor Inspector and justified as high risk in operation of the equipment for catastrophic incident.
      Major indications: These are those indications that are observed by the third party inspector or vendor inspector and can potentially influence or reduce the operation traits of the system to be examined.

      Minor indications: Those indications that, according to the third party inspector/vendor inspector evaluation, do not affect the correct use/destination of the examined system, piece of equipment and/or individual component.

      The lighting during the examination may be natural or artificial, provided the lighting quality and intensity are suitable and sufficient to enlighten, with the required uniformity, the part to be controlled. The minimum lighting condition for visual inspection is 500 LUX. The contrast of direct or indirect visual observations is considered proper when a black line, 0.8 mm thick or less - drawn on a neutral grey sheet positioned on or near to the area to be examined - can be seen clearly.
      The acceptability limits of the defect are dependent on the applicable specification and/or the requirements of the customer. Dimensional controls are carried out by the inspector right from the start, and material receiving inspection is very important item and must be done based approved inspection and test plan.

      This material which is to be subject to visual examination must be positioned in the best possible way to facilitate maximum viewing ease. These are conducted by instruments which have been calibrated previously and have been accepted to be the best by quality control personnel.
      All the measurements which are done are marked by the use of a red pencil on the inspectors drawing copy. All these measurements should match with the specifications of the customer. The schedule for sampling of these products is conforming to the international standards if they are applicable in the case.

      Upon completion of the visual examination by the TPI inspector, then issues a visual and/or dimensional check certificate. This certificate gives out the date of examination, the examination technique (which can be direct or indirect) applied in addition to all identification references for the area concerned, the component or the equipment piece that is a subject to be examined and signed for performance.

      All observed defects, irrespective of whether they're acceptable or unacceptable, are clearly reported on the certificate and treated in according of quality plan.

      I hope this content to be useful for engineers that are involved in quality control process in manufacturing shop. I will be happy to reply your technical questions about this subject.
      regards
       
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    3. hgtyu123

      hgtyu123 New Member

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      There are 4 supplementary articles in this regards. There are Dye penetration examination, magnetic particle examination, radio graphic and ultrasonic testing. all are accompanied by visual inspection. You may review them in industrial inspection article in detail.
       

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