Non destructive testing

Non Destructive Testing

Non-Destructive Testing (NDT) refers to an array of inspection methods that allow inspectors to evaluate and collect data about a material, system, or component without permanently altering it.

At Cookson & Zinn we use a variety of testing techniques, to comply with specific standards or codes that are required for products used in different industries or as part of our own internal Quality Assurance programme.

X-Rays in non-destructive testing

Radiography testing (X-Ray testing)

X-ray testing is used to create a detailed image of an object’s internal structure. X-ray is a suitable method for weld inspections because you do not have to alter or destroy the object to thoroughly analyse it. X-ray is also a flexible method that can be used on almost any material.

X-rays require access to two opposite sides of the weld. On one side, the source transmits radiation into the object, while on the other side a detector film records the differences in absorption to develop a clear image. The film or digital image serves as a permanent record of the inspection.

Why welds?

Welds are a vital part of component construction and must meet applicable codes and standards. In addition, welds can face prolonged exposure to intense forces even during regular operation. Over time, some welds can begin to show signs of deterioration or damage. It is important to inspect the base metal, weld material, and heat affected zones of welds – as even small flaws can progress into larger issues over time.

X-Ray testing examines the welded area and look for discontinuities in welds such as Cracks, Cold Lap, Cluster Porosity, Internal Concavity, Incomplete Penetration, Incomplete Fusion or Slag Inclusions.

Ultrasonic non-destructive testing

Ultrasonic testing is the process of  transmitting high-frequency sound waves into a material in order to identify changes in the material’s properties.

In general, Ultrasonic Testing uses sound waves to detect defects or imperfections.

The most common Ultrasonic Testing methods is the pulse echo. With this technique, our inspectors introduce ultrasonic sound into the weld area and measure the echos (or sound reflections) produced by any imperfections found in the material as they are returned to a receiver.

Ultrasonic testing

Magnetic particle non-destructive testing

Magnetic Particle Testing is the act of identifying imperfections in a material by examining disruptions in the flow of the magnetic field within the material.

To use Magnetic Particle Inspection, inspectors first induce a magnetic field in a material. After inducing the magnetic field, the surface of the material is then covered with iron particles, any flaws in the weld area will produce a disruption in the flow of the magnetic field. These disruptions create visual indicators for the locations of imperfections within the material.

Dye penetrant non-destructive testing

Dye Penetrant Non-Destructive Testing (also called Liquid Penetrant Testing) refers to the process of using a liquid to coat material and then looking for breaks in the liquid to identify imperfections in the material.

Inspectors conducting a Penetrant Test will first coat the material being tested with a solution that contains a visible or fluorescent dye. The dye is made up of very fine particles that can penetrate into any small cracks or defects. They then wipe the surface clean removing any extra solution from the material’s surface while leaving the solution in any defects in the material’s surface. After this, inspectors use a developer to draw the solution out of the defects. The dye is a contrast colour that shows once the developer is applied. Ultraviolet light is used to reveal imperfections for fluorescent dyes.


Pressure testing

Non destructive pressure testing

Pressure Testing is a non-destructive test performed to ensure the integrity of the pressure shell.

Pressure testing is generally used in 2 specific applications;

  • is used as a method for checking for minor defects or “leaks”
  • Vessels that are required to contain a pressure in excess of 0.5 Bar and falls under the requirements of PD5500:2021

Testing methods

We use a number of different methods for pressure and leak testing:

  1. Hydrostatic testing, which uses water or another liquid under pressure
  2. Pneumatic or gaseous-fluid testing, which uses air or another gas under pressure
  3. A combination of pneumatic and hydrostatic testing, where low pressure air is first used to detect leaks
  4. Initial service testing, which involves a leakage inspection when the system is first put into operation
  5. Vacuum testing, which uses negative pressure to check for the existence of a leak