Nondestructive Testing – Merrill Tool & Machine

Nondestructive Testing (NDT)

Nondestructive test (NDT) methods offer an effective way to determine part integrity without destroying or compromising the part. Merrill uses a number of NDT procedures for:

• Failure analysis
• Casting integrity
• Verification of critical features that cannot be inspected or measured by other means

We apply NDT to a wide range of materials such as castings, plastics and composites. All testing procedures are certified by an ASNT Level III inspector if required and can also be validated by a third-party audit.

Magnetic Particle Inspection

Eddy Current Testing

Fluorescent Penetrant Inspection

Ultrasonic Testing

Leak Testing

Radiographic Testing

Magnetic Particle Inspection

Magnetic particle inspection (MPI) detects minute cracks that are open to the surface in ferrous materials. It is best used for detecting cracks that are not visible to the naked eye; however, the cracks must be at or near the surface to be detected.

Eddy Current Testing

Merrill Tool & Machine uses eddy current testing (ECT), also known as electromagnetic testing (ET) to quickly check for threads, stress corrosion cracking and wall thinning at a part’s surface or subsurface. ECT can also be used to detect coating thicknesses.

ECT works by using an excitation coil to introduce an alternating electromagnetic field into a part. A detector coil picks up a magnetic signature. This signature is compared to the range of signatures of good parts. A crack or geometrical defect will significantly alter the electromagnetic signature and the part will be rejected. ECT is used on conductive materials (both ferrous and non-ferrous).

Fluorescent Penetrant Inspection

Fluorescent penetrant inspection (FPI) is a cost-effective way to detect surface cracks in ferrous, non-ferrous and even non-metallic parts. Merrill Tool & Machine uses FPI for weldments, castings, forgings or any other part that is prone to surface cracking.

In FPI, a dye is applied to the surface of the material and penetrates into any surface defects or cracks. When the surface is wiped clean, the dye remains visible in the cracks.

FPI is also known as fluorescent dye penetrant, liquid penetrant and dye penetrant testing (PT).

Ultrasonic Testing

Ultrasonic testing (UT) is a cost-effective method to find flaws in materials, measure casting wall thickness and evaluate some material properties. It can only be used to inspect materials capable of sound wave penetration, including any metallic and some non-metallic materials.

UT can use both scanning and immersion techniques. A high-frequency sound wave is introduced to the part and is reflected by defects or the internal surface of a casting. By measuring the elapsed time and known speed of sound in the given material, the depth of a defect or thickness of part can be accurately measured. Other ultrasonic methods involve looking at the echo signature of the reflected sound wave. Using UT is limited when materials are too thick, multilayered or contain air gaps.

Leak Testing

Leak testing (LT) is used for locating and measuring leaks in sealed components; determining weld, seam and joint characteristics; and validating the integrity of vacuum furnaces. Merrill uses a Varian 979 helium leak detector, which can accurately measure leaks down to 10E-10 atm cc/sec. It is calibrated to traceable NIST standards.

Leak testing is more accurate, sensitive and reliable than other commonly used methods such as decay and bubble testing. Most LT systems use a combination of evacuation and sniff-testing to accurately measure pressure loss and leak rates. In sniff-testing, the part is pressurized with helium and scanned with a sniffer probe attached to the inlet of the leak detector. The helium leaks are measured by a helium-tuned mass spectrometer. To quantify the leak rate, a pressurized part is placed into a vacuum chamber where total helium can be detected. Leak rates can also be quantified as a whole or by isolating individual leak sites.

Leak testing is also known as leak tightness, vacuum testing and helium mass spectrometer leak detection (HASID).

Radiographic Testing

Radiographic testing (RT) is an excellent method to study the internal geometry of components. The process uses X-ray to focus on very small areas internal to a component. It can be used for failure analysis to pinpoint the location and nature of a failure and can also be used to test pressure vessels, piping and welded assemblies.

RT works with virtually any material, including thick materials, multi-layer composites and materials with air gaps. However, it is expensive and limited in the size of parts it can accommodate.