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What are non destructive testing methods

by Jul 15, 2020Weld Testing

Cleaner, smaller, faster and better – original equipment manufacturers (OEMs) demand these attributes for emerging technologies and innovations in such fields as aerospace, chemical engineering and healthcare. This post explores what are non destructive testing methods to ensure OEMs receive flawless raw materials or components for quick, problem-free production.

Manufacturers use non destructive testing methods on a variety of materials to detect any potential defects and discontinuities, while maintaining the functionality of custom fabrications, components or assemblies. Applying non destructive testing methods to materials and components safeguards end products from faults and production systems from errors. For example, an undetected single flaw in a weld could introduce a series of events that damages or destroys an entire system.

Testing certainly provides a better yield – but faster? Yes, non destructive testing is a valuable time-saver when considering the costs associated with remedying a faulty product line or damaged system. Non destructive testing methods are integral to production at Axenics and have been since our doors opened in 1984.

Contract manufacturing is a highly competitive field where lead time and pricing are hot topics. Skipping the step of non destructive testing is not an option – nor will it ultimately save anything, especially a company’s reputation, once damaged goods arrive. Testing and trust go hand in hand for quality manufacturers.

Prevalent methods of non destructive testing include, but are not limited to:

Visual Testing

Visual inspection is a vital method of evaluating materials for potential defects or leaks, as well as an opportunity to audit production consistency. Visual inspections often pair with other non destructive testing methods, such as ultrasonic testing or helium leak testing.  A visual inspection varies depending on the make of material, as stainless steel and thermoplastics have differing characteristics. While customer or legal standards can vary for each project, visual testing detects potential problem areas, such as:

  • Banding distortion
  • Material corrosion
  • Material inconsistency
  • Surface flaws
  • Weld fissures

“We visibly inspect our own welds using a borescope to check inside a tube or pipe down to the root of the weld. This makes sure we achieved 100% penetration and uniformity on the weldment. Once I find it satisfactory, quality control takes it further with additional testing,” said Ernest Coolong, an Axenics welder who specializes in tungsten inert gas (TIG) welding on stainless steel. Axenics’ welders are D17 certified by the American Welding Society.

Ultrasonic Testing

Clean technology advances are a boon for alternative energy manufacturers. Hydrogen fuel cells provide safer, cleaner solutions for companies that produce consumables. Water is the byproduct of hydrogen fuel cells, so forklifts and other vehicles with that technology installed can perform alongside food products without contaminating them.

Axenics provides non destructive testing on materials and weldments for three-pass heat exchanger hydrogen fuel cells for a variety of vehicles, such as lift trucks or buses. An ultrasonic gauge sends high-frequency mechanical vibrations into a component or material. Once the wave has penetrated the entirety of the component, two audible signals result from the gauge. If there is a third audible signal, a deformity exists that goes beyond acceptable parameters. For example, a scratch on tubing cannot be greater than 10% of the wall thickness of the material, or else it’s rejected.

Dye Penetration Testing

Weldments on hydrogen fuel cells are often the width of a single strand of human hair, so depth gauges may not detect a fault in a weld. A dye penetration test searches for minuscule cracks that visual and other testing methods cannot locate. Steps for this testing method include:

  • Cleaning the material to remove any dirt, dust or potential contaminants and then drying the material
  • A thin dye coats the material, and then the dye is wiped clean from the material
  • Next, the material is sprayed with a developing powder
  • The powder is wiped from the material
  • If flaws exist, any remaining powder exposes them
  • Depending on the type of dye used, a flaw is visible by the human eye under white light or black light

Helium Leak Test

Helium leak testing is a valuable non destructive method performed on piping, tubing, valves, manifolds, tanks and other components used to transport liquids or gases. Helium leak testing helps prevent equipment failure, operational down times and potential workplace hazards.

“Finding leaks is vital so production can go on at a high level,” said, Dave Scott, who oversees stainless steel quality inspection at Axenics. “Our eyes miss tiny cracks in gas or liquid delivery systems because of the minuscule size of the leak. Helium testing detects little leaks without having a negative impact on the system. Plus, helium tests won’t leave behind any substances that can damage a system.” 

Helium is the element of choice for several reasons:  

  • Safety: Helium is non-toxic and nonflammable, a huge positive for technicians performing the tests
  • Speed: The inert gas consists of minuscule atoms with low viscosity, resulting in quick travel through a component
  •  Accuracy: Helium finds the smallest leaks in materials
  • Simple detection: Helium has good separation from other gases, making it easily detectable

Wise manufacturers can avoid component failures or malfunctions by incorporating helium leak testing into their production systems. OEMs use testing to ensure the safety of technicians, operations and facilities, as well as the environment, if storage tanks on the property are used to hold or transport chemicals.

Leak testing extends the life of materials because problems are identified early, which means they can be immediately addressed. Helium leak testing also provides a marketing advantage to OEMs: companies spread the word regarding the high-quality standards they maintain with their equipment to build trust in their operations.

Two common helium leak methods are vacuum testing and pressure testing. Both use a mass spectrometer leak detector, which consists of an ion source, ion trap and a separation system.

Vacuum Helium Testing Process

Material testing from the outside-in uses a vacuum pressure method. First, a product goes into a hermetically-sealed chamber. Next, all air is pulled from both the chamber and product. Then, helium pumps into the chamber to monitor gas concentration. The concentration of helium alters when a leak is present in the chamber, which triggers an audible alarm on the mass spectrometer.

Pressure Helium Testing Process

This method checks for leaks from the inside-out. First, helium or a mixture of helium and nitrogen pressurizes a product. Then, a sniffer probe attached to the mass spectrometer scans potential leak points inside the product for traces of escaped helium.

Hydrostatic Testing

This test utilizes water pressure to identify potential leak points. Hydrostatic test steps include:

  • Completely filling a component with water (or a dyed liquid)
  • Placing the component into a tank
  • Adding air pressure to the component in excess of its normal operating pressure (This factor of safety is typically 143, 150 or 166.66% of the designed working pressure)
  • Holding air pressure for a predetermined time frame
  •  Any pressure changes indicate leaks in the component’s structure or weldments

Non Destructive Testing Best Practices

Quality control for existing vendors

Even trusted suppliers are fallible. Testing a sample on certified, pre-tested materials is wise. Your longtime vendor may have changed their third-party machining vendor unannounced, resulting in materials that are slightly different from your previous order. A size variation of even 30/1,000-inch can make a big difference when it comes to critical production. Evaluate materials and fittings for a slip in quality and make an inquiry if you find something unusual.  

“We’ve run into instances straight from the mill. We have found defects in stainless steel tubes using a borescope with a camera,” said Tom Hammer, a welder with Axenics. “We take photos inside the tubes to detect any deformities. In one situation, the dye that the vendor passed through the tube was breaking down and leaving scratches and inclusions on the inside of the tubes. When you catch and reject entire lots of metal, a faulty product never makes it to your customer, inevitably saving all of us money and time.”

Cleanroom assembly and welding

Non destructive testing on raw material is pointless if the other steps in the manufacturing process occur in a “dirty” environment. Controlling contamination during every stage is a top priority for manufacturers working with components used to produce products for healthcare industries or the sciences. A cleanroom is an ideal purification solution for every aspect of production, from inspecting materials through final testing and packaging.

Generally, cleansing of tools occurs before they enter a cleanroom. Paper and cardboard are banned from the area. Regular vacuuming, dusting and inspections are required maintenance for a cleanroom environment. Air purification/filtration systems remove tiny contaminants, and technicians wear suits, gloves and footwear to cover all extremities in an effort to contain skin flaking and getting onto components (which sounds gross, but it can happen).

Understand your limitations

Manufacturing technology changes faster than we can produce an article about non destructive testing.  Some of your customers may seek testing beyond your current capabilities. For example, Axenics occasionally receives requests for component pressure tests higher than 3200 psi – not safe for their current environment. To avoid in-house danger and to maintain customer satisfaction, they use trusted third-party testing facilities or laboratories for certain non destructive tests, such as radiographic testing using x-rays.

This blog post answers the questions:

  • What is non destructive testing
  • What are non destructive testing methods?

What is non destructive testing?

Non-destructive weld testing is true to its name as it does not mandate that a completed weld must have its functionality destroyed in order to determine its quality. The most-common non-destructive weld tests we would use for your components are hydrostatic testing and helium leak testing.

What are non destructive testing methods?

Prevalent methods of non destructive testing include, but are not limited to: visual testing, ultrasonic testing, dye penetration testing, helium leak testing and hydrostatic testing.

Do you have low-pressure canisters that need to be requalified?

Axenics is DOT certified for this type of testing. Contact Us to learn more.

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