Testing & Inspection
NON-DESTRUCTIVE EXAMINATION
RADlOGRAPHIC EXAMINATION
 
Radiographic examination is based on the principle that extremely high frequency light waves, usually x-ray or from a radioactive source such as Cobalt 60, will penetrate solid materials and, when projected onto a photosensitive film, will reveal voids, areas of discontinuity, and lack of homogeneity. This examination is widely used in evaluating the soundness of welds and in general, is limited to evaluating butt welds of parts of substantially the same thickness and material. In the case of bellows, this is normally limited to the evaluation of longitudinal seam welds before forming.

Unless required by the purchaser, radiographic examination of the longitudinal seam of a bellows need not be specified. Examination of the longitudinal seam can be accomplished by some other means, such as liquid penetrant examination. If a radiographic examination is required on the longitudinal seam of a bellows then it should be performed before the bellows is convoluted. After the forming operation, it is usually not possible for the source or the film to be placed to yield a meaningful radiograph.

Radiographic examination of the bellows attachment weld should not be specified. Interpretation of such radiographs is impractical due to the weldment geometry, differences in thickness and penetrability. In view of the above, and recognition of the attachment weld as a seal weld, non-destructive examination of this weld should be accomplished by some other means such as liquid penetrant examination.
LIQUID PENETRANT EXAMINATION
 
Liquid penetrant examination consists of cleaning a surface, coating it with a dye, wiping the dye off and coating the surface with a developer which after sufficient time will draw the dye from the cracks, pin holes, and make them apparent to the observer. Liquid penetrant examination is limited in scope to detecting surface indications such as fine hairline cracks, pin holes and weld roll-over. With the thin material used in bellows, the probability of any defect remaining subsurface is unlikely. This examination is frequently used in evaluating bellows welds. The bellows base material may also be inspected by this method but shall be performed prior to convolution forming. The developer used in this procedure acts as a blotter; therefore, when rechecking a questionable indication it is absolutely essential to re-clean that area and reapply dye and developer. Unless otherwise specified, examination procedures shall conform to the requirements of ASTM-E165.
MAGNETIC PARTICLE EXAMINATION
 
Magnetic particle examination consists of coating a surface with finely powdered iron and establishing a magnetic field in the material being examined. The presence of discontinuities or irregularities in the magnetic field, as indicated by the lines of powdered iron, will indicate surface and also subsurface defects, cracks, slag inclusions, and lack of weld penetration, This examination is limited to magnetic material and will not indicate deep subsurface defect. Although generally used for examination of welds, it is possible to examine base material if there is reason to suspect material defects such as laminated plate.
ULTRASONIC EXAMINATION
 
Ultrasonic examination uses high frequency sound waves to detect flaws, and is useful in determining thickness, depth, and exact location of defects. Interpretation of indications in sections of sharply varying thickness is difficult. The examination is not limited to any group of materials.
AIR JET LEAK EXAMINATION
 
Air jet leak examination utilizes compressed air is directed through a nozzle on to a small area between two welded parts. A leak detector solution is applied on the opposite side of the welded connection which will bubble up if the compressed air is able to pass through the weld. This examination is useful on low pressure. Expansion Joint bellows end connection welds where other forms of examination and testing are not practical.
PRESSURE TESTING
 
Hydrostatic and pneumatic are two types of pressure tests that can be performed on an Expansion Joint. Hydrostatic pressure testing involves filling the Expansion Joint with a liquid, usually potable water, while pneumatic pressure testing involves filling the Expansion Joint with air or other gas. After the Expansion Joint is filled it can then be pressurized to the required test pressure. Pneumatic pressure testing is hazardous and it is recommended that special precautions be taken.

In the Expansion Joint industry, it is frequently the practice to hydrostatic pressure test an Expansion Joint to one and one-half times the design pressure or pneumatic pressure test it to 1.1 times the design pressure at ambient temperature. Expansion Joints placed in high temperature service may require the pressure test be performed at an adjusted pressure. It is imperative that the test pressure does not produce a membrane stress in excess of yield strength or cause permanent deformation or instability (squirm) of the bellows at test temperature. It may be necessary to reduce the test pressure adjusted for temperature, to the maximum pressure that will not exceed yield or cause instability.

An Expansion Joint should not be subjected to a test in the field at a higher pressure than was used in the manufacturer's shop without the manufacturer's knowledge. All anchors and guides must be installed and shipping devices removed prior to such testing. In the case of large Expansion Joints, additional supports may be required to support the weight of the water used during hydrostatic testing.
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