Case Study Information
A stand-off Raman spectrometer has been developed to make observations of liquid samples within a gas pipeline. The instrument is based on a static Fourier Transform spectrometer. The high etendue offered by the instrument enabled four liquid samples to be measured from a distance of 2.4m within a gas pipeline. Liquids were identified with depths of less than 5 mm demonstrating the concept is viable for active pipeline measurement.
The Challenge
Liquid contamination within gas pipelines presents a significant operational challenge for the gas processing and transmission industry. Substances, including glycols, compressor oils, and process liquids, can damage compressors and associated infrastructure if not effectively detected and removed.
Traditional laboratory-based analytical approaches can require physical sampling and lengthy turnaround times, delaying operational decision-making. In many cases, rapid identification of the contaminant is critical in determining the appropriate response and minimising disruption to pipeline operations.
Any solution also needed to operate within the constraints of active gas transmission infrastructure, including:
- Non-invasive measurement requirements
- Remote stand-off operation
- High-pressure operating conditions
- Integration with existing pipeline infrastructure
- Compact, field-deployable instrument design
The Solution
To address these challenges, IS-Instruments developed a stand-off Raman system based on a static Fourier Transform spectrometer using spatial heterodyne spectroscopy (SHS). Unlike conventional dispersive Raman systems, the SHS architecture offers an exceptionally high etendue, enabling significantly higher light-collection efficiency while maintaining the required spectral resolution. The design also eliminates moving parts, improving robustness for industrial deployment.
The instrument was configured with remote projection optics mounted on the pipeline standoff assembly, with the primary instrument unit and laser housed remotely and connected via 100 m fibre-optic cables. Operating at 785 nm, the system was designed to maximise Raman signal collection while minimising fluorescence effects.
Key Features
- Stand-off Raman measurements at distances of approximately 2.4 m
- Detection of liquid layers with depths below 5 mm
- High-etendue SHS spectrometer architecture
- Static Fourier Transform spectroscopy with no moving parts
- Remote fibre-coupled operation
- Operation within pressurised gas pipeline environments
- Rapid, non-invasive liquid identification
Experimental Testing
The system was tested at pressurised pipeline facilities operated by GL DNV in the UK, including sites at Loughborough and Spadeadam.
Trials were conducted using five representative liquid contaminants:
- Xylene
- Methanol
- Tri-ethylene glycol (TEG)
- Mono-ethylene glycol (MEG)
- Compressor oil
Successful Raman measurements were obtained across liquid depths of 2-20 mm, with all target liquids yielding measurable spectra within the required observation time.
| Parameter | Value |
|---|---|
| Integration time | <10 min |
| Distance to target | 2.3 m |
| Maximum aperture | 70 mm (diameter) |
| Minimum amount of liquid | 2 mm in depth |
| Resolution | 4 cm -1 |
| Spectral range | 400 – 2800 cm -1 |
Project Outcome
The project demonstrated the viability of a new class of stand-off Raman instrument for active pipeline monitoring applications.
By exploiting the high-etendue advantage of spatial heterodyne spectroscopy, the system enabled efficient collection of weak Raman signals under challenging industrial conditions. The technology demonstrated the ability to rapidly identify liquid contamination events without requiring physical sampling or interrupting pipeline operation.
The work highlighted the potential for Raman-based sensing systems to support real-time monitoring, operational efficiency, and improved process assurance within gas transmission infrastructure.
Further Information
Full technical paper available here.
