What Is FTIR? And How Is It Used in the Petroleum Industry?

Bearings and lubrication play an important role in many mechanical operations in the petroleum industry. From simple wheel bearings on trolley jacks to complex lubricants and bearing systems, operating under extreme conditions. Often overlooked, bearings often take the most stress in a system whilst operating safely and vibration free.

Essential to a bearing’s operation is the lubricant. Without lubrication a system might quickly fail as the moving parts seize up. Making sure that the lubricant is fit-for-purpose is a critical part of any maintenance schedule. Even better is the ability to quickly and routinely check the lubricant, and Fourier transform infrared spectroscopy (or FTIR) offers this ability. But what is FTIR? And do I need a laboratory to work in?

Infrared Spectroscopy

Infrared spectroscopy (IR) is an analytical technique that uses light from the infrared part of the spectrum to analyse a sample. The peaks in an IR spectrum correspond to the vibrational frequencies of the chemical bonds in the sample. Because each compound has a unique arrangement of atoms, no two IR spectra are the same. So IR provides an identification of the chemical groups in a sample. Based on the size of the peaks, modern software can be used to give an indication of the amount of material present too, meaning IR is a useful tool for both qualitative and quantitative analysis.

What is the FT in FTIR then?

The first IR instruments separated the infrared light from the source into individual frequencies using a prism or diffractive grating. The sample was then exposed to the individual frequencies one at a time. The detector measured the intensity of light transmitted through the sample at each frequency and generated a plot.

This was a time consuming process taking several minutes for each scan. However, modern instruments overcome this slow scanning process using a device known as an interferometer and some clever mathematics. An interferometer is an optical device that allows the sample to be scanned by all of the frequencies at once — in a process taking a second or so. The signal at the detector, the interferogram, contains all of the information about every frequency emitted by the source. To interpret the information we need to decode the interferogram — with the decoding carried out using a mathematical technique known as Fourier Transform (FT).

Portable FTIR

Whereas older IR instruments are large and confined to laboratories — FTIR instruments can be small and portable due to the increased use of electronics. This allows the instruments to be used in the field as a powerful tool in an engineer’s toolkit.

By comparing the spectra of used oil with fresh oil, a technician can determine the degradation and contamination of oil in a few seconds. FTIR is a recognised technique for lubrication analysis and is recommended by many international testing bodies as discussed in this article: Used-Oil Analysis Using a Portable FTIR Spectrometer.