A Non-Destructive Examination (NDE) refers to a process to detect the presence of physical defect or flaw, of a part or component, without damaging or destroying the material being examined. It is also known as non-destructive testing (NDT.)
Pump parts, or components, that are usually subjected to NDE include pressure containment castings such as casing, cover, nozzle head, barrel, etc. They also include parts such as impeller, shaft, bearing housing, etc. NDE does not replace, but supplements, the need for hydrostatic testing of pressure containment parts of pumps.
The commonly used Non-Destructive Examinations (NDE) are:
Magnetic particle examination (MPE)
Liquid penetrant examination (LPE)
Visual inspection - visual examination of the surface is done to look for obvious material defects and dimensional irregularities. This is usually part of a vendor's standard quality control program, and the examination is done at no added cost - the other types of NDE are provided at extra costs.
Magnetic particle examination (MPE) - performed on ferromagnetic materials with calibrated equipment using both "dry" and "wet" methods. In dry method, a dry colored powder is used to provide sufficient contrast with the material being tested. An electrically operated yoke is used to induce a magnetic flux into the surface being examined.
Liquid penetrant examination (LPE) -performed on nonmagnetic castings using certified liquid penetrant materials in a spray booth under carefully controlled temperature and pressure.
Radiographic examination - this examination may use X-ray, iridium, or cobalt radiographic material to obtain films to identify surface and subsurface defect, or flaw.
Ultrasonic inspection - are performed using beams of high frequency sound waves, above 20 khz, to detect surface and subsurface defect, or flaw.
Eddy-current inspection - uses the interaction between metals and electro- magnetic fields to detect quality issues. Eddy-current inspection is more suited for automated production line and is not widely used in the pump industry.
Defects, or flaws, to be examined include casting shrinkage, slag and sand inclusions, surface (gas) porosity, linear defect (discontinuities), hot tear, chills and chaplets, cracks, weld or weld-repair defect, etc.
Of the most commonly used NDE methods, MPE and LPE are commonly used for surface detection, whereas radiography and ultrasonic are the preferred methods for subsurface detection, of defect or flaw.
The use of NDE can also be applied in equipment design such as to increase the allowable working pressure (MAWP) of a pump, or to decrease its size and weight which is very important in some services such as in offshore oil platform. Read the discussions in the full-version of this article [ * ].
Personnel performing NDE must be fully qualified to perform the examination in accordance with applicable industry standards such as ASME, ASTM, MIL STD, etc. The NDE may be performed at the foundry, or at the vendor's manufacturing facility.
Related topics: [ * ]
Procedures and acceptance criteria for magnetic particle examination (MPE) Procedures and acceptance criteria for liquid penetrant examination (LPE) Procedures and acceptance criteria for radiographic examination Procedures and acceptance criteria for ultrasonic inspection
[ * ] Some information are excluded in this article. Read more.