Non-Destructive Examinations (NDE)


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:

  • Visual inspection
  • Magnetic particle examination (MPE)
  • Liquid penetrant examination (LPE)
  • Radiographic examination
  • Ultrasonic inspection
  • Eddy-current inspection


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.


R:0110-NODE
C: manufacturing, design
F: nde


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