National Techincal Services Time of Flight Diffraction

Performing time of flight diffraction inspection on the weld of a tank shell

Rapid Weld Inspections

Time of flight diffraction (TOFD) is an ultrasonic screening tool that can rapidly scan welds and produce very accurate measurements of any defects found.

TOFD operates using a pitch and catch technique with two probes on either side of a weld. One probe transmits a series of ultrasonic pulses and another receives them. If a crack or other defect is present in the weld, the ultrasonic waves will diffract and the time of flight between transmitter and receiver will be affected. Based on the change in time of flight, weld defects can be located and sized.

Sensitive and Accurate

TOFD is more reliable than traditional radiographic inspections, and the costly issues associated with using hazardous radiography—shutdowns, evacuations, etc.—are eliminated.

In addition, TOFD:

  • inspects many welds very rapidly
  • accurately measures defects, regardless of the defects' orientation
  • is extremely sensitive, even when used with thick walls.

A Complementary Technique

TOFD is used in conjunction with other NDT techniques because it is of its inability to reach two dead zones around the weld: one near the surface, the other at the back wall.

To inspect the dead zones, one technique commonly used with TOFD is phased array ultrasonic testing. National Techincal Services provides phased array testing, as well as a host of NDT services for all your inspections needs.

Highly Trained Technicians

TOFD offers the benefits of rapid testing to obtain very accurate measurements. But to ensure full benefits are reaped requires highly trained technicians.

National Techincal Services’s teams of technicians, inspectors, and analysts have the training and experience to perform TOFD efficiently as well as any complementary testing it may require.