25-08-2017, 09:32 PM
PIPE SURFACE INSPECTION BY INDUSTRIAL MACHINE VISION
PIPE SURFACE INSPECTION.pptx (Size: 1.69 MB / Downloads: 26)
Introduction
The act of inspecting piping systems via video inspection/ hydraulic and pneumatic pressure testing and other non destructive procedures
If we are not careful …
Injuries and human fatalities
Pollution (air & water)
Millions of dollars in costs
Pipeline accident costs in the US from 2000-2010
–25 fatalities, 37 injuries
–$102,963,379
Laser shearography for inspection of pipelines
Shearography is a highly sensitive laser optical measuring technique to record very small deformations and strains.
Because local defects in components generally cause little additional strain on its surface, it is possible to use shearography for non destructive inspection purposes.
A very well suited application of shearography to non destructive testing is the inspection of piping.
Principle of the testing technique
It is a laser optical measuring technique which is able to measure the smallest deformations and strain concentrations on the surface of a component.
If a defect causes, on the visible surface of this component, a local strain concentration due to mechanical loading, shearography will show this effect.
Shearography can be used for fast and non-destructive inspection of large components, because it is a full-field measuring technique of very high sensitivity (some micro strains)
Procedure
The piping to be inspected is loaded with inner pressure change.
The piping will expand only by some micrometres. In the areas with a weakened wall, e.g. caused by corrosion, the wall of the pipeline is deformed by the pressure more than in areas without defects (see Fig. state 1 and state 2).
The difference between a loaded and an unloaded state provides information about the deformation of the wall of the pipeline.
The deformation gradient is obtained by deriving the deformation curve in the axis of the pipeline.
It indicates the respective area of strain concentration of the defect.
Measuring system for shearographic pipeline inspection
A mobile inspection system is used to apply shearographic pipeline inspection.
It consists of a portable testing head and also carries the video camera.
The illumination and observation optics are directly attached to the pipe.
The laser light is either supplied from a laser station via flexible glass fibre cable to the testing head or a laser diode is directly integrated into the testing head.
The area of the pipe which is inspected at any given time depends on the size of the testing head and the power of the laser light.
Generally it is approximately 300 x 220 mm 2 (DIN A4 size,vessels up to some square metres have been inspected simultaneously).
Advantages
Inspection from the outside of the pipeline;
Fast inspection (inspection time approx. 1-2 minutes per image);
Pipeline surface needs no special preparation (painting can remain on the pipe;
Wall thinning bigger than 15% of the original wall thickness are detected (depending on inspection pressure and pipe geometry);
Planiform inspection, therefore 100% control;
Application of shearographic pipeline inspection
Consequently the new technique is valid for application especially in the following fields:
Fast inspection of big pipeline systems or vessels;
In preventive maintenance for status test;
100% control of safety relevant pipelines;
Inspection of cooling water pipelines in power plants;
Inspection of pipeline systems in chemical industries.