J. Ray McDermott

CHALLENGING PROJECTS. IT’S WHAT WE DO.

J. Ray McDermott

NON DESTRUCTIVE TESTING

J. Ray McDermott

J. Ray McDermott

Ultrasonic Testing

Sound waves are propagated by Piezoelectric crystals

Ultrasonic Testing uses mainly two types of waves, longitudinal and shear waves

In steel Longitudinal waves travels at the speed of 5920 M/sec and Shear waves travel at 3230 M/sec

A pulse is transmitted and received back by the crystal, the information is processed by the machine, the time taken is calculated to give the depth of the reflector

J. Ray McDermott

Ultrasonic Testing

A couplant is used in between the probe and the test part to remove the air

The machine is calibrated using a known thickness block before to set the range before scanning the test material

Discontinuities can be detected with the exact depth

It gives optimum reflection from planar type of discontinuities such as laminations, lack of fusions, cracks

J. Ray McDermott

Magnetic Particle Inspection

Magnetic flux lines travels by the least resistant path and they do not cross each other

There is a flux leakage when the flux lines travels across a discontinuity

When fine iron powder in a liquid bath is sprayed on the magnetized part, they get attracted at the flux leakage and display a visible image of the discontinuity

The powder concentration in the liquid bath is 1.2 to 2.4 ml/100ml

J. Ray McDermott

Magnetic Particle Inspection

The lifting power of the yoke is 4.5 kg

Field indicators are used to demonstrate the adequacy of magnetic field

Two types of techniques are used, Longitudinal magnetization and Circular magnetization

Longitudinal field can be detected, Circular field is contained within the material and cannot be detected unless there is a flux leakage

J. Ray McDermott

Magnetic Particle Inspection

MPI is applicable only on ferromagnetic material, it can detect both surface and subsurface defects, up to 6mm using the prod method

J. Ray McDermott

Radiographic Testing

The commonly used source is IR-192 or X-ray

The radiation emitted penetrate steel, for testing welds, the source is placed at a distance from the weld and on the other side of the weld a film is placed in a light proof pvc cassette sandwiched in between two lead intensifying screens

A set of wires of different diameters called IQI or Penatrameter is placed in between the source and the object to verify the sensitivity of the radiograph

J. Ray McDermott

Radiographic Testing

An exposure is made for the required time depending on the thickness and the source to object distance

The film is then taken to the dark room for processing

It goes through the process of developing and fixing

After processing and drying the film, it is viewed on a illuminator. Voids in the weld are displayed as dark images as more radiation passes through voids in the given time as against uniform material

J. Ray McDermott

Radiographic Testing

Planar types of discontinuities are difficult to be detected, volumetric and spherical discontinuities are more easily detected

The films can be kept as a permanent record

The depth of the discontinuities cannot be assessed in the radiograph

J. Ray McDermott

Liquid Dye Penetrant Testing

Liquid Dye penetrant testing can be used on all non porous surfaces

It can only detect discontinuities that are open to the surface

The first step is to clean the surface of all discontinuities that can mask the discontinuity

The part is then sprayed with liquid dye penetrant to cover the entire area of interest, it is kept for the required dwell time normally from 10 to 15 minutes

J. Ray McDermott

Liquid Dye Penetrant Testing

The liquid dye penetrant enters the discontinuity by capillary action

The part is then cleaned, initially with lint free rags and then with rags moistened with solvent, care is taken not to remove the penetrant from the discontinuity

A developer is then sprayed on the part, it provides both contrast and blotting action pulling out the entrapped penetrant from the discontinuity

J. Ray McDermott

Liquid Dye Penetrant Testing

The red penetrant is blotted out and gives a clear red indication on white back ground

The part is then cleaned of all residues