TOFD Time-Of-Flight Diffraction

SonoInspec can assist you in setting up your non-intrusive inspection (NII) plan, whereby the aim is to keep your production and HSE performance to the highest level by executing non-intrusive non-destructive testing while the plant is in full operation.

SonoInspec uses TOFD inspections to keep your production at the highest level

The SonoInspec team has a long-standing experience with the use of the TOFD (Time-of-flight diffraction) technology on very high temperatures. The team has executed ultrasonic weld inspections on client assets up to a temperature of 475°C (887°F).

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Benefits of TOFD

Fast & accurate inspection, direct results, no radiation

Weld inspections at high temperature

Inspection of “Golden” welds at pre-heat temperature

For weld inspections & wall thickness mausurements

The high temperature TOFD NII inspection capability is an excellent inspection method for weld inspections, but also wall thickness measurements with TOFD line scans, when the regular high temperature ultrasonic corrosion mapping tools are not sufficient anymore. Up to 350°C (662°F) SonoInspec has standardised and validated the TOFD inspections as per the ISO pre-service standard for pressure equipment (EN-ISO 10863) in the thickness range of 6mm up to 100mm.

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TOFD inspection

Successful validation for a client at 300°C (572°F)

Successful validations and inspections have been executed at 300°C (572°F) at a client’s vital reactor with a wall thickness of 270mm. Accurate calculations about sound wave paths at these temperatures are made in advance. The TOFD high temperature inspection capability is extremely suitable to be used for monitoring purposes of known cracks.

Our partners include:

Sintra Engineers
Waygate Technologies
NDTS India
Sonotech Trinidad

Finding cracks using TOFD

TOFD is a very accurate inspection technology based on sound wave, travelling from the transmitter to the receiver and from the tips of cracks (diffract the signals). Both longitudinal and transverse sound waves can be used to achieve the highest POD. With TOFD you can accurately measure length, depth, and height of the indications in your weld. TOFD is normally not used for characterisation of the indication, like slag inclusion etc.

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Finding cracks with TOFD

With TOFD there’s no need to abandon the area like with radiography

TOFD inspections are a cost reducing and fast alternative to radiography inspections. As TOFD does not work with radiation, you do not need to abandon the area like with radiography. The inspections can be done at day shift, data is digitally stored, and results can be made available immediately. Inspection productivity is much higher as with radiography especially when the wall thicknesses increase.

Inspection of welds on the critical path of the planning, the so called “golden” welds can be inspected with TOFD at pre-heat temperature when the weld is only partly finished. This reduces the chance for rejections and time losing repairs, after the weld has got its final inspection.

Want to learn more about TOFD?

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Frequently Asked Questions

How does TOFD work on partially filled welds?

The ultrasound travels through the material following the material geometry. Measurements are taken with the backwall as reference. The lateral wave is significant larger in these situations, but this will be overcome by making a scan every X millimeters the weld is filled up during the welding process. The inspection can be executed at pre-heat temperature (~180°C / 356F) and on objects with a nominal wall thickness of 20mm or thicker. The first pass can be done when the weld is 1/3 filled. The benefit of this inspection is that the chance that you have a repair at the end is reduced to an absolute minimum.

Till what temperature can you use TOFD?

TOFD has been applied to 485°C (905°F). Where it can be applied depends on an number of factors. Material type should be C-steel. The smallest defect you want us to find and the wall thickness of the material.

What is the approach for a high temperature inspection with TOFD?

It depends on the object and what you want us to find. The best way is to make a sample, machine in artificial defects which have to be found and heat it up to the temperature on which the inspection has to be done. If the defects can be found, the setups are validated. We have a set of ISO pre-service flat plates to cover 6-100mm on several other samples from other projects on which we have done testing to 350°C (662°F) and higher temperatures.

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