Ferrous and Nonferrous Metal Testing
A weld may look flawless on the surface yet conceal a hidden crack, while a steel bar marked with the correct grade may still have the wrong chemical composition. Metals tend to fail in ways that cannot be seen from the outside: a void inside a weld, a coarse grain structure, a pipe wall that has quietly thinned. That is why metal testing brings together two kinds of work. Metallurgical testing looks at what the metal is made of and how it is built, while non-destructive testing (NDT) looks for flaws without damaging the part.
At METS Laboratories, we cover both for ferrous and nonferrous metals, with a strong focus on metallurgy, NDT and ultrasonic testing, so that manufacturers, fabricators and plant owners can confirm their metal parts are fit for use before they go into service.
What Are Ferrous and Nonferrous Metals?
The difference comes down to iron.
- Ferrous metals: these contain iron. Carbon steel, alloy steel, stainless steel and cast iron are the common ones. Most are strong and magnetic, though some stainless grades are not, and many rust without protection.
- Nonferrous metals: these contain little or no iron. Aluminium, copper, brass, bronze, titanium, nickel alloys and zinc are typical examples. They resist rust, and many are light or carry heat and electricity well.
- Alloys: most metal in use is an alloy, a mix of elements, so a small change in composition can change how it performs.
- Why it matters for testing: the type of metal decides which methods will work. Magnetic particle testing, for example, only works on magnetic metals.
Importance of Metal Testing
A metal part is trusted to carry load, hold pressure or resist heat and corrosion, and testing is how that trust is earned.
- Grade checking: 304 and 316 stainless steel look the same, but they do not behave the same in a corrosive setting. Only chemical analysis tells them apart.
- Safety: a small internal crack can grow under repeated load until the part fails.
- Weld quality: welds are often the weakest point in a structure, so codes ask for them to be inspected.
- Ageing plant: pipes, tanks and vessels lose wall thickness to corrosion over time, and measuring it shows how much life is left.
- Specifications: projects and buyers set test requirements, and the report is the proof that they were met.
- Cost: finding a fault before installation costs a replacement part. Finding it in service can cost a shutdown.
What is Metallurgical Testing?
Metallurgical testing examines the composition, strength and internal structure of a metal, usually on a sample cut from the material.
Chemical Composition
- Optical emission spectrometry (OES): a spark analysis that gives the percentage of each element in steels and alloys, including carbon.
- X-ray fluorescence (XRF): a quick way to identify an alloy without cutting it, often used for positive material identification (PMI). XRF cannot measure carbon, so steels needing a carbon value go to OES.
Mechanical Properties
- Tensile test: pulls a specimen until it breaks to find strength, yield and elongation (ASTM E8/E8M, ISO 6892-1).
- Hardness test: Rockwell, Brinell and Vickers methods show resistance to indentation (ASTM E18, E10, E92).
- Impact test: the Charpy test shows toughness, often at low temperature (ASTM E23, ISO 148-1).
Microstructure and Corrosion
- Metallography: a polished and etched sample is studied under a microscope to see grain size, phases and inclusions.
- Corrosion tests: salt spray and intergranular corrosion testing for stainless steel show how a metal will cope in service.
- Failure analysis: works out why a part broke, whether from fatigue, overload, corrosion, or poor heat treatment.
Non-Destructive Testing of Metals
Non-destructive testing checks a part for flaws without cutting or damaging it, so the part can still be used afterwards. The right method depends on the type of flaw, where it sits and what the metal is.
- Visual testing (VT): the first and cheapest check.
- Liquid penetrant testing (PT): finds cracks that reach the surface in any non-porous metal.
- Magnetic particle testing (MT): finds surface and near-surface cracks in magnetic metals only.
- Eddy current testing (ET): finds surface flaws in conductive metals, including aluminium and copper alloys.
- Radiographic testing (RT): uses X-rays or gamma rays to image internal flaws.
- Coating thickness testing: magnetic and eddy current gauges measure the dry film thickness of paint and other coatings on ferrous and nonferrous metals (ASTM D7091)
- Ultrasonic testing (UT): uses sound waves to find internal flaws and measure thickness, as explained below.
Ultrasonic Testing and How it Works
Ultrasonic testing sends high-frequency sound waves into a metal and reads what comes back.
- Surface preparation: loose scale and paint are cleared, and a couplant such as gel or water is applied so the sound can pass from the probe into the metal.
- Transmission: the probe sends a short pulse of sound into the part.
- Reflection: the sound travels through the metal until it meets the back wall or a flaw, and part of it bounces back.
- Reading: the instrument shows the echoes on a screen. The time between pulse and echo gives the depth, and the height of the echo points to the size of the reflector.
- Evaluation: the result is compared with the acceptance criteria in the code or specification.
What Ultrasonic Testing Can Find
- Cracks, lack of fusion, and incomplete penetration in welds
- Porosity and slag inclusions
- Laminations in plate
- Internal defects in forgings, castings and bars
- Wall thinning from corrosion or erosion
Common Ultrasonic Techniques
- Thickness gauging: measures the remaining wall of pipes and tanks from one side.
- Phased array ultrasonic testing (PAUT): a probe with many small elements steers the beam and produces a cross-section image, which makes weld inspection faster.
- Time-of-flight diffraction (TOFD): uses sound diffracted from the tips of a flaw to size cracks accurately.
Strengths and Limits of Ultrasonic Testing
- Strengths: it finds flaws deep inside a part, needs access to one side only, gives results straight away and uses no radiation.
- Limits: it needs a smooth surface and a couplant, and results depend on operator skill.
- Coarse-grained metals: cast iron and some stainless steel welds scatter the sound, which makes the signal harder to read.
- Calibration: sound travels at a different speed in each metal, so equipment is set up on a reference block of the same material.
- Common standards: EN ISO 17640 for welds, ASTM E114 and E164 for contact testing, and ISO 9712 for the qualification of NDT personnel.
Who Needs Metal Testing?
Anyone who makes, buys, welds or maintains metal parts can use the results, including oil and gas operators, fabricators and welding contractors, manufacturers, plant operators, and metal traders checking grades.
Why Choose METS Laboratories for Metal Testing?
Range of tests, quality system and the people doing the work all count when you pick a provider. Here is what we offer.
- Destructive and non-destructive work together: one provider for metallurgical testing and NDT
- An accredited laboratory: our laboratory holds ISO/IEC 17025 accreditation, and ASTM D7091-22 for coating thickness is within its scope
- A trained team with metallurgy experience: our team has good hands-on experience in metallurgical testing and NDT
- Middle East presence: laboratories in Qatar and the UAE
- A wider network: METS Laboratories also has laboratories in the UK, China and India
Conclusion
Metal fails where it cannot be seen, so testing has to go beyond the surface. Metallurgical testing confirms what the metal is and how it was made, and non-destructive methods such as ultrasonic testing show what is inside it without damaging the part. Together they are what good ferrous and nonferrous metal testing is built on: a record that fabricators, plant owners and buyers can rely on. If you have parts, welds or samples to check, send METS Laboratories the metal type, the specification and the tests you need, and our team will advise on the next step.
Frequently Asked Questions
1. What is the difference between destructive and non-destructive testing?
Ans: Destructive tests, such as tensile and impact tests, damage a sample to measure its properties. Non-destructive tests, such as ultrasonic and penetrant testing, check the part itself without harming it.
2. Which NDT method only works on ferrous metals?
Ans: Magnetic particle testing (MT). It needs a metal that can be magnetised, so it works on carbon and low-alloy steels, cast iron and ferritic or martensitic stainless steels. It does not work on nonferrous metals such as aluminium, copper alloys and titanium, or on austenitic stainless steels such as 304 and 316, which are non-magnetic.
3. Can ultrasonic testing find surface cracks?
Ans: It is mainly used for internal flaws. Cracks that reach the surface are usually found more easily with penetrant, magnetic particle or eddy current testing.
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