Forensic Engineers & Investigators
Metallurgical Analysis and Materials Science
The analytical services that we provide in metallurgy and materials science are set out below.
Metallography: This method involves cutting a cross section through an area of interest such a crack or corrosion pit in metal component. The section is mounted in plastic then polished and etched to enable an optical microscope to reveal critical detail. This analysis may concentrate on the microscopic structure of the metal and its relationship with the defect to determine whether the problem was caused by inherent defects from the manufacturing process or whether the component was subject to adverse environmental or operational factors.
Chemical analysis: The chemical composition can be evaluated to determine whether the alloy has been manufactured in accordance with its material specification or if a deviation can explain the features identified from the metallography exercise.
Mechanical and physical testing: The strength, hardness and ductility of the metal are commonly checked to determine whether it complies with its specification and is fit for purpose. The results are often correlated with chemical analysis, metallography and SEM/EDS evaluation.
Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDS): These analytical instruments are used to evaluate the microscopic structure and fracture of metals and other materials. They can provide critical information on physical and chemical interaction of the material with its operating environment and are useful for analysing contaminant traces and small debris particles.
Case study: corrosion pitting and cracking of a heat resistant steel tube.
Steel tubes in a critical industrial heat exchanger had suffered repeated failures due to pitting, cracking and accelerated wastage. In our investigation a defective tube was removed and after inspection was sectioned and subject to metallography, followed by detailed analysis utilising scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS). The purpose of the analysis was to determine how the protective oxide scale had performed in protecting the surface of the alloy steel tube from its corrosive environment.
As the following images show, variations in crack morphology indicated that stress levels had been high and of variable magnitude. Analysis of the scale showed complex foliated layering and composition variation possibly due to varying stress levels and changes in the environment as the scale formed. The composition changes and associated void formation reduced the adhesion of the scale, compromising its ability to protect the underlying alloy tube. The resulting damage allowed corrosion pits to form and a fatigue crack then developed in the most severely damaged zone.
