General Principles of Radiography :
The part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation.
The film darkness (density) will vary with the amount of radiation reaching the film through the test object.
Tag: radiography
What Is Radiation:
X and Gamma Rays are a family of waves that are called electromagnetic waves. X-rays and gamma rays differ only in their source of origin. X-rays are produced by an x-ray generator and gamma radiation is the product of radioactive atoms. They are both part of the electromagnetic spectrum. They are waveform, as are light rays, microwaves, and radio waves. X-rays and gamma rays cannot been seen, felt, or heard. They possess no charge and no mass and, therefore, are not influenced by electrical and magnetic fields and will generally travel in straight lines. However, they can be diffracted (bent) in a manner similar to light.
Properties of X Ray & Gamma Rays:
Each photon contains a certain amount (or bundle) of energy, and all electromagnetic radiation consists of these photons. The only difference between the various types of electromagnetic radiation is the amount of energy found in the photons. Due to their short wavelength they have more energy to pass through matter than do the other forms of energy in the electromagnetic spectrum. As they pass through matter, they are scattered and absorbed and the degree of penetration depends on the kind of matter and the energy of the rays.
post emulsifiable liquid penetration testing: It is divided in to two category:
- Method B: Post-Emulsifiable, Lipophilic
- Method D: Post-Emulsifiable, Hydrophilic
Water-Washable, is the most economical method & it has not replaceable for rough casting surface, threaded & key surfaces.
- Water-washable or self-emulsifiable penetrants contain an emulsifier as an integral part of the formulation.
- The excess penetrant is removed from the object surface with a simple water rinse.
- Penetrant materials have the property of forming relatively viscous gels upon contact with water, which results in the formation of gel-like plugs in surface openings.
- While they are completely soluble in water, given enough contact time, the plugs offer a brief period of protection against rapid wash removal. Thus, water-washable penetrant systems provide ease of use and a high level of sensitivity.
5. Inspection:
Inspection with visible dye penetrant with minimum whate light intensity 100 foot-candles or 1100 lux shall follow. Ultraviolet (UV-A) radiation of minimum intensity 1,000 micro-watts per centimeter squared is common, along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after 10- to 30-minute development time, and is dependent on the penetrant and developer used. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws.
6. Post Cleaning:
The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are recommended as per PT procedure.
Penetrant Classification System
Penetrants Type:
Type 1 Fluorescent Dye
Type 2 Visible (Red) Dye
Removal Method:
Method A Water Washable
Method B Post Emulsifiable, lipophilic (oil base)
Method C Solvent
Method D Post Emulsifiable, hydrophilic (water base)
Removers
Class 1 Halogenated (non-flammable)
Class 2 Nonhalogenated (flammable)
Class 3 Special Application
Developers Form:
Form a Dry Powder
Form b Water Soluble
Form c Water Suspendable
Form d Nonaqueous Type 1 Fluorescent (solvent based)
Form e Nonaqueous Type 2 Visible (solvent based)
Form f Special Application
Fluorescent Sensitivity*
Level 1/2 Ultra Low
Level 1 Low
Level 2 Medium
Level 3 High
Level 4 Ultra High
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