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This case study was quite unique and is an indication of the versatility at One Eighty Materials Testing. Our diverse team of scientists and engineers can effectively develop test methodologies for a wide variety of investigations. We aim to consistently provide meaningful insight to our clients and this investigation is an example of such work.

One Eighty was approached by a client from the liquor industry who experienced failure of plastic sight glass in their process equipment. The client wished to understand the cause of the failure of the part and called upon One Eighty Materials Testing to perform the analysis.

One Eighty Materials Testing has twenty years of experience in root cause failure investigations in a wide range of industrial sectors. Our customers have come to know and rely on our systematic approach to these investigations.


Since limited information was available on the material of the sight glass, we decided to conduct a variety of characterisation experiments to identify the polymer of construction. This information, in turn, helped to identify the root cause of fracture in the sight glass. Optical microscopy and other analysis techniques were used to determine the initiation point of the cracks in the sample. This proved to be vital in understanding whether any mechanical or environmental factors were responsible for the failure.

The OEMT team were able to accurately characterise and identify the polymer of the sight glass. The interaction between the identified polymer and the specific process fluid in the system was thus identified as a potential issue.

What we found

Optical analysis and electron microscopy provided further validation for this hypothesis – showing that the crack propagation originated from the interior of the pipe (see Figure 1 & 2 below). Internal crack initiation is an indication that the failure is not likely due to mechanical damage but was rather caused by solvent damage and/or environmental stress cracking.

Figure 1: Close-up of the fractured piece showing cracks propagating from the interior of the pipe

Figure 2: SEM image showing cracks propagating from the interior of the pipe


It was recommended that compatibility tests should be conducted between the replacement material for the sight glass and the process fluid to ensure that the sight glass can remain in service for as long as possible. OEMT was also willing and able to support the client in the material selection process should this be required.

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