Measurement Services

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Ferrite testing is a fast, inexpensive, and accurate way to measure delta ferrite content in austenitic and duplex stainless steels. Proper ferrite content provides a balance between ductility, toughness, corrosion resistance and cracks prevention. Heat, pressure and caustic environments require materials and welds with very high metallurgical integrity. A correct ferrite measurement can help to avoid both solidification cracking and corrosion in stainless steel welds, pipes, plates, pressure vessels and petrochemical components. 

When ferrite content is too high, stainless steel can lose ductility, toughness, and corrosion resistance – especially at high temperatures. If ferrite content is too low, stainless steel welds become susceptible to hot cracking or solidification cracks. In duplex stainless steel welds, a deficit of ferrite content can also reduce weld strength and contribute to the development of stress corrosion cracks.

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Ultrasonic Flow Measurement involves the use of ultrasonic transducers. The flow meter can measure the average velocity along the path of an emitted beam of ultrasound, by averaging the difference in measured transit time between the pulses of ultrasound propagating into and against the direction of the flow or by measuring the frequency shift from the Doppler effect. It is used to analyse the volume of liquid flow.

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Grain Size Measurement is useful in metallurgy, to determine the grain sizes in various materials. Grain sizes depend upon a lot of factors such as heat treatment, alloy conditions, working conditions etc. Grain size measurement is useful mostly during and after manufacturing and heat treatment, so as to ensure proper working and treatment has been carried out.

Grain sizes can be measured by means of Ultrasonic Testing. Sound waves are reflected off the various grain boundaries. Depending upon the number and size of grains, the reflections and diffractions of the sound waves can be measured, thereby giving an indication of the number and size of grains present in the material. Grain size is then calculated as per various standards.

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Carbon in the form of graphite is often used as an additive in the production of cast iron, amounting to 2 to 4 percent by weight or 6 to 10 percent by volume in typical castings. The microstructure of graphite within cast iron has major effects on the casting’s mechanical properties. When graphite arranges itself as thin flakes the result is grey iron, which is hard and brittle. When graphite takes the form of spherical nodules the result is nodular iron, which is soft and malleable.

Both grey and nodular iron are made by mixing carbon, silicon, and other additives into molten iron, and often part of the mixing is done in the final mold. If the mixing is non-uniform or the casting process is otherwise imperfect, it is possible to make a casting with variations in nodularity, or pockets of grey iron within a nodular iron casting. Because this will significantly change the mechanical properties of the metal, foundries need to check nodular iron for uniformity. It is important that both the distribution of graphite in the casting be uniform, and that graphite inclusions be of the right form (nodules rather than flakes).

Microscopic examination and tensile strength tests are effective for checking nodularity, but for quick and non-destructive evaluation of a casting the preferred method is ultrasonic testing based on the fact that nodular iron and grey iron have different sound velocities.

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Pressure Distribution Measurement involves measurement of pressure applied by a component over an area, and determination of whether the pressure is as required. Pressure application is important in various press-fit and other such components. It is also important in various assemblies. Pressure applied by each component, and its distribution over the surface can be determined.

Measurement is carried out by use of a special film – PRESCALE. A pressure inspection sensor on the entirety of the film allows confirmation of pressure distribution of the entire surface at a glance. The colour appears red where pressure is applied, and the colour density varies according to the amount of pressure. The microcapsules in the colour-forming layer are broken by pressure, and the colourless dye is absorbed into the developer, causing a chemical reaction to produce a red colour. The microcapsules containing the colour-forming material are adjusted to varying sizes and strengths, and is coated uniformly, producing a colour density that corresponds to the amount of pressure.

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Velocity Measurement is a special application of Ultrasonic Testing, which is used to determine the acoustic velocity of various materials. Different materials have different acoustic velocities, depending upon their constitution. As the constituents, and their individual concentration within a material varies, its acoustic velocity also varies. Measurement of acoustic velocity provides ideas about the elastic properties and thermodynamic properties such as density, isothermal compressibility and heat capacity.

The equipment is first calibrated by measuring the thickness of a material of known thickness and velocity, such as standard steel calibration blocks. The corresponding measurements are noted and echoes are calibrated. Once calibration is completed, a material of known thickness, whose velocity is to be determined is scanned. This thickness should preferably be equal to the calibration block thickness. The system would then provide echoes based on the thickness and velocity of the material, in terms of steel equivalent (or equivalent to that of the material used for calibration). If the thicknesses are same, the velocity of the material would be inversely proportional to the difference in thicknesses indicated.  For a material with a lower velocity, a higher thickness would be indicated since the sound waves have to travel for a greater amount of time before generating an echo. Similarly, if the velocity is higher, a lower thickness would be indicated. The ratio of the indicated thickness and the actual thickness would be inversely proportional to the ratio of the sample and the calibrated thicknesses. Thus, velocity of the sample can be found out. If the sample thickness is not same as the calibration block, additional factor depending on the thickness would have to be considered.

While this technique may be used to determine velocity of all materials, solid and liquid, any liquid with a specific gravity greater than that of water may require an additional liquid, with a known velocity, having a specific gravity greater than that of the liquid to be measured, so as to generate a good echo