I would like share with you about a useful article about visual examinations that are done in industrial equipment in construction process.
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.
When examining a welding the examination needs to be very thorough. The inspection must be in a way to detect probable defects such as under cutting, slag inclusion or craters. The actual examination that is based on national and international standards for the weld and surface examination processes are classified 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.
The lighting for the examination can be either natural or artificial, it does not really matter. The only condition here is that the lighting should illuminate the surface to be examined in a uniform and a controlled manner. To achieve this, the minimum lighting that is required is 600 LUX. There is proper contrast if there is a black line that can be drawn on a grey background that is no more than 0.8 mm thick and when placed on the surface to be examined, is 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.
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 detected defects in visual examination process must be expressed in inspection visit report and inspection certificate. This must be done irrespective of acceptance or rejection of the indications.
I hope this post be useful for all engineers that are involved in the industrial equipment construction.
babak