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FTIR: Fourier transform infrared spectroscopy of oil and gas coatings

Since 2011, TWI has carried out on-site Non-Destructive Inspection (NDI) FTIR of over 500 downstream oil and gas components at three sites in the UK to ensure they have been coated with the specified material that imparts both corrosion resistance and appropriate surface characteristics. The inspection also ensures that there is no presence of a specific potential additive within the coating, which affects the mechanical function of these parts in service.  The inspection certificate is a mandatory document required for the coating acceptance procedure as defined by the customer, a major global player.

The inspection is carried out using a portable FTIR instrument from Agilent (Exoscan 4100), which has a number of interchangeable objectives to accommodate different forms and shapes of the material to be analysed. The objectives comprise:

  • Diamond ATR (flat surface) – good for liquids and soft solids
  • Diamond ATR (curved surface) – good for harder materials and films
  • Specular reflectance – good for smooth reflective surfaces
  • Diffuse reflectance – good for rough irregular surfaces
Figure 1: FTIR Instrument and different interchangeable objectives
Figure 1: FTIR Instrument and different interchangeable objectives

Capability and uses

The instrument, when used with the most appropriate objective, in this oil and gas case, specular reflectance, can be used to analyse almost any surface type including absorbing and scattering surfaces, coated reflective metal surfaces, films, in addition to bulk materials including powders, liquids and granules.

The instrument is widely used at TWI for many projects, both internal and external. Specific uses include bulk material identification, identification of contamination on surfaces, characterisation of surface coatings and failure analysis.

The process is quick (~15 seconds per spectrum), non-destructive and non-intrusive, which is ideal for a number of development and safety critical applications where coatings or layers of surface material cannot be removed from the part to be analysed. Indeed, in the case of the diffuse reflectance objective, the assessment can be completely non-contact, with the sample surface around 10mm away from the instrument.

TWI’s expertise

The portable nature of the instrument means that trained TWI staff can carry out FTIR analysis both off-site and in the laboratory. Subsequent analysis of the data can be carried out off-line by the appropriate expert within the company. Once the spectra have been acquired, TWI has access to a large spectral database to ensure accurate and rapid material identification. In some instances further analysis may need to be carried out using TWI’s benchtop FTIR microscope (spot size ~20microns) and Scanning Electron Microscope (SEM). This combination, along with other analytical capabilities, makes the FTIR instrument an indispensable tool in the area of acceptance test, material characterisation and failure investigation for clients at any location.

For further information about this capability and how it might be used/adapted for other applications please email contactus@twi.co.uk

Figure 2: The FTIR instrument in use
Figure 2: The FTIR instrument in use
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