Visual Examination of Surfaces
02-17-2013, 12:09 PM (This post was last modified: 05-19-2013 09:41 PM by kjki456.)
|Visual Examination of Surfaces
Hi, I would like share a content about visual examination that are done by inspection engineer on the industrial equipment and components.
This article defines staff qualification, equipment, procedures and certification for visual examination in third party inspection (TPI Inspection) services according to job specifications and customer requirement for general use. The personnel in charge of NDT Testing, visual and dimensional controls must have a good knowledge and experience in fabrication and manufacturing processes and are subject to periodical sight testing.
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 which needs to be controlled has to be on an accessible plane and must allow visual examination from 600 mm of distance and an approximate 30 degree angle. This is to facilitate the detection of visible surface defects like scratches, corrosion, and cracks.
If the area that has to be examined is a weld, then we need to do a deeper examination in the form of detecting possible craters, under cuttings and slag inclusions.
According to the national and international standards for visual examination, the factors for observation must be considered as below:
Critical indications: Those indications that, according to the third party inspector and industrial vendor Inspector evaluation, may be detrimental for the correct use/destination of the examined system, piece of equipment and/or individual component.
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.
Indications which are minor: These are the kind of indications detected by the TPI inspector which do not undermine the correct usage of the system, part or the individual component in any way.
In this regard the lighting in the inspection room must be of optimum quality. It can either be naturally lit or artificially provided but it should be sufficient to carry out the inspection procedure according to the standards which have been set. This makes the required amount of light close to 500 LUX. The contrast can be suitably adjusted when a black line drawn on a grey sheet positioned to the area of examination can be seen with clarity. The black line should be at least 0.8 mm in thickness.
The defect acceptability limits depend on the applicable specification and/or customer requirements. Dimensional controls are carried out by the inspector during all fabrication and manufacturing steps requiring such controls starting from received material control, in according with quality plan.
Materials, components or pieces of equipment subjected to dimensional control are positioned in a way so as to allow the best possible control conditions. Dimensional controls are carried out only by instruments, equipment and means previously inspected and accepted by the manufacturer quality control department.
The inspections of the measurements during the surface examination are marked in red by a pencil on the drawing copy by the inspector. The measurements are then checked for compliance to tolerance. The schedule of sampling for the dimensional controls lot follows the international standards wherever it is applicable.
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 defects that detected in the visual inspection process regardless to acceptance or rejection must be reported and stated in the certificate.
I hope this will be useful for you. I will be so happy to answer to your questions.
02-17-2013, 02:06 PM
|RE: Visual Examination of Surfaces
Is there any applicable NDT measure to inspect TS coating?
03-09-2013, 12:21 PM
|RE: Visual Examination of Surfaces|
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