Corrosion

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  • Topic: X-ray, Radiography, Building insulation
  • Pages : 13 (4394 words )
  • Download(s) : 22
  • Published : December 9, 2012
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Abstract

The ingress of moisture into the insulation system and the consequential concentration of chlorides in the insulation enhance the corrosion of insulated parts of the installation. Moisture may even lead to the concentration of corrosive substances from the atmosphere in the insulation system. Therefore consideration must be given to how corrosion of the object can be prevented through appropriate anti-corrosion applications and/or design of the insulation system. Where pipelines are insulated or lagged, such as ammonia and steam lines, the damage of the insulation is certainly a sure event with much more probability. Corrosion under Insulation (CUI) is a multi-billion dollar problem that destroys expensive industrial infrastructure. It is difficult to detect due to the insulation that covers the location of the corrosion or erosion. Corrosion under insulation measurement in process equipment and piping is necessary required to determine corrosion rates, Wall thickness, and remaining life and will be used for Risk Based Inspection (RBI), environmental safety and for insurance purposes. So, there are much more methods to be practicable in this respect but the most probable in this regard will be Computerized reporting, is possible with comparison to previous results for the determination of rate of material loss and the remaining life of the pipeline.

Profile Radiography

A comprehensive explanation of this technique, also called "Profile Radiography" or "Tangential Radiography" and Wall-thickness measurement of insulated piping is a typical NDT-application in the chemical and petrochemical industry The Radiographic source could be a X-Ray machine or a radioactive isotope. The greatest contrast is usually obtained with X-Rays then Gamma-rays, such as produced by Selenium-75 and Iridium-192.Tangential imaging is normally not carried out with X-rays. Here the parts of radiograph which lie below the tangential location on the pipe only are interpreted. The middle part of the pipe image is ignored. To get the proper image at tangential location, the energy of radiation used must be higher than that used for double wall inspection of the same pipe. This technique requires harder radiation, because the tangential arrangement leads to great materials-thicknesses (and also great changes in materials-thicknesses) to be penetrated by the rays. The whole concept of tangential radiography is to penetrate the sidewall of the pipe so that the thickness is projected on to the imaging material and corrosion can be detected.

Procedure:

A suitable source to object distance must be chosen to reduce the geometric unsharpness of the image. The image may be captured on conventional x-ray film which will then be processed in the normal way by developing, fixing and drying and then viewed on a viewer and the dimensions of the image will be measured on the film with the appropriate correction being made for any magnification caused by the object to film distance.

Determination of the wall thickness t by measuring the distance t´ on the film. This way is called "Tangential Radiography" and requires the film to be applied flat (not adapted to the curvature).This causes the limitation of the method. Radiographic wall-thickness measurements of insulated piping in the chemical and petrochemical industry are typically carried out by exposing film-cassettes with Ir 192 as -ray source. The radiographic image of the tube/pipe is then evaluated off-line after the film is developed Film-less Radiography

It can be used with phosphorescent storage imaging plates.
which are then read in a special reader and a digital image captured and displayed on computer monitor where dimensions can be measured with the appropriate software.

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