Detecting Various Levels of Color for LNG – ASTM D156, D6045

A Guided Wave Saybolt Color Analyzer System was fully implemented for real-time color measurement of various grades of LNG (liquefied natural gas) product with multiple specification requirements.

The Customer

The customer is a leading natural gas pipeline operator. Currently, they own over 71,000 miles of pipeline that move natural gas, natural gas liquids (NGLs), refined products, and crude oil. The company trucks both in-spec and out of spec LNG products to meet customer demand.

The Problem

The inbound LNG product is maintained at a different specification than the outbound/exported LNG product. Color analysis is necessary for both the in and outbound LNG product because in each case, the customer requires a high degree of accuracy and repeatability that is reliable and consistent to third-party standards.

The customer was looking for an analyzer to measure the Saybolt color of the LNG flowing in their pipeline.

The Challenge - Detecting Various Levels of Color

LNG is natural gas cooled to a liquid state. Natural Gas is composed primarily of methane, but may also contain propane, ethane, and other heavier hydrocarbons as well as small residual quantities of N2, O2, CO2, H2O, and some sulfur-containing compounds. Prior to liquefaction, these residual materials are removed with only clean hydrocarbons remaining. The composition of natural gas can vary slightly from different producing locations.

Typically LNG is a colorless material, but during distillation, the carryover of larger hydrocarbons (C6+) can affect the color of the LNG (the typical specification for C6+ in LNG is 0 to 0.05%).
Measuring the Saybolt or ASTM color online is a key parameter in many light hydrocarbon mixes for quality control to detect this carryover. Monitoring the color allows the refiner to verify that the product is within specification. Any “out of spec” product can be reprocessed before being sold. Saybolt Color (ASTM D156) measures yellowness and has a scale that ranges from -16 (darkest) to +30 (lightest). Figure 2 shows the Saybolt measurement scale on a Guided Wave Saybolt Analyzer.

The Solution

By using a Guided Wave Saybolt Color Analyzer system, the customer was able to accurately measure this color change with repeatable values. Guided Wave provided a complete ready-to-go solution which included a 50 mm pathlength SST probe, fiber optic cables for remote processing, control software and Saybolt application calibration. The analytical calculations are all encoded in the software so answers and alarms are clearly reported.

The Smart Choice

The customer came to Guided Wave because our Saybolt Color Analyzer is a complete solution that provides accurate, real-time, reliable results. The analyzer employs a dual-beam design – meaning; the system has a continual internal optical reference check that allows it to self-compensate for signal variation due to non-sample conditions. This technology provides long-term stable readings offering laboratory grade results from a process analyzer. It consistently measures the color variation without interference from other factors.

Its linearity and repeatability, as well as its low maintenance requirements, make it a cost-effective, smart choice to help optimize production, improve yields, ensure consistent product quality and enhance profitability.

  • Unique dual-beam optics - for long-term, stable operation
  • Up to two (2) independent measurement points - for added analytical flexibility at the reduced cost per point
  • High efficiency yet rugged fiber optics - analyzer electronics can be located away from a hazardous sample point
  • In-door touch screen or Ethernet (Modbus TCP) - easy local or remote analyzer operation and control
  • Analytical calculations are all encoded in the software - answers and alarms are clearly reported

The Conclusion

This customer has been successfully operating the Guided Wave Saybolt Color Analyzer for over a year. They have also purchased additional analyzers, as well as recommended the Saybolt Color Analyzer to other companies in this industry as the standard to follow for this process.

The Proof- Continuous Accurate Saybolt Color Measurement
Figure 1 shows a typical trend chart monitoring the Saybolt color of a continuous flowing process. Figure 2 shows an initial calibration chart showing the measured values as compared to laboratory standard values. For more information see Guided Wave's Saybolt Color Analyzer data sheet #1062 and LNG Application Note #3080.


Figure 1


Figure 2

Control You Can Measure
By partnering with Guided Wave customers gain the advantage of 30+ years of experience in online process monitoring and stream sample analysis. We deliver a total solution that includes optically matched components and a well-planned calibration approach leading to long-term success and savings. Our entire product line is designed and developed to provide real-time data of laboratory quality while thriving in the most demanding processing plant environments. Choose Guided Wave - for the control you can measure.