Extracting oil from subsea wells is more expensive and challenging than in surface production systems. Mechanical equipment such as subsea control modules, hydraulic fluid accumulators and valve manifolds are used to control the production process in subsea and surface levels. The equipment therefore must be designed to withstand extreme operating conditions such as high oil temperatures and high external and internal pressures.
In general, the costs associated with the repair or replacement of subsea equipment is huge. Hence, offshore platform operators aim for certified clean equipment that are free of particle-based contaminants which lead to failure, damage, or wear.
Glycol fluids meet specific cleanliness classification codes that are used in various cleanliness standards such as ISO 4406, SAE AS4059 and NAS 1638. This article describes the use of glycol fluids for monitoring cleanliness in subsea oil production equipments.
Glycol Analysis Using Liquid Particle Counters
Typical microscopes and laboratory liquid particle counters have been widely used to monitor the cleanliness of hydraulic fluid. Laboratory liquid particle counters have delivered promising results, but showed inconsistent performance in testing the cleanliness of glycol fluid.
However, recent innovations in liquid particle counter design by Hach Ultra, combined with sample handling procedures produce consistent glycol analyses results. As a result, the amount of time and sample volumes required for the analysis of glycol fluid samples have been reduced.
Liquid particle counters which feature light-blocking sensor technology are incapable of differentiating solid particles and air bubbles. Entrained gas from the fluid sample can be eliminated or minimized through sample handling practices.
Sample Handling Best Practices
This section describes important sample handling procedures:
Using Clean, Glass Sample Containers
Before collecting the sample, it is essential to flush the sample container two or three times using the fluid to be analyzed. Visual inspection of samples in glass containers is much easier. Plastic sample containers, however, introduce solid contaminants or chemical compounds which cause foaming. Only one type of hydraulic fluid, such as oil- or glycol-based fluids, can be used in sample containers to avoid cross contamination.
Minimizing Entrained Gas and Bubbles
Entrained gas is a key factor which produces inconsistent liquid particle counter test results. In order to ensure reproducible and accurate particle counting results, glycol fluid samples need to be bubble-free. Large gas bubbles can be eliminated by sonicating the sample or pulling a vacuum on the fluid sample.
However, small, invisible bubbles can be removed based on the indications of the sample such as the formation of foam or bubbles on the sample surface and appearance of sample as sparkling water.
Ball valves fixed at sample ports can be used to reduce the amount of entrained gas present in the fluid samples. Avoiding the use of needle valves and gear pumps can reduce the development of small invisible bubbles in the sample.
Analyzing Fluid Samples Only Once
The fluid sample in the container can be pressurized using carbon dioxide or clean air thereby delivering a force to move fluid through the liquid particle counter. This gas is soluble in glycol fluids. By removing the gas pressure, the fluid sample tends to de-gas. The residual bubbles can be counted as particles while analyzing the fluid sample during pressurization.
Maintaining Fluid Samples at Room Temperature
Certain anti-foam agents added to the glycol fluids can solidify at temperatures below room temperature. These solids will be counted as particles by the liquid particles counters. Hence, such samples should be maintained at room temperature before analysis.
Placing Sample Ports in Strategic Locations
Samples can be obtained from several key locations to achieve best fluid-cleanliness results and to reduce the probability of entrained air. Fluid samples can be taken on the discharge side of the equipment being flushed and also downstream from pumps.
Solutions for Glycol Cleanliness Monitoring Applications
Although highly labor intensive and subjective, laboratory microscopes are one of the most commonly used methods of analyzing contamination in glycol fluid. Upon passing the fluid sample via a membrane disc filter, a technician checks and counts the particles on the filter media using the microscope. The quality of analysis depends on the technician’s experience while evaluating the particles on the filter.
Offshore equipment manufacturers, however, employ other instruments which deliver NAS code outputs for monitoring the glycol fluids. Most of this equipment is operated based on a differential pressure measurement for calculating NAS codes. They require 2l sample and 5mins of testing time, approximately, to complete a single analysis.
Liquid Particle Counting Advances
The use of microscopes for particle counting has reduced in recent years, and offshore equipment suppliers started to focus on fluid cleanliness testing using laboratory particle counters such as the HIAC 8011.
Particle counters offer greater flexibility in selecting the appropriate protocols, more reproducible analysis results, and are less time-consuming. As a result, it is possible to achieve greater throughput in their filtration processes.
In addition, with the recent developments in liquid particle counter technology such as the HIAC GlyCount, it is possible to have point-of-use and on-line glycol cleanliness monitoring processes. The HIAC GlyCount offers fast cleanliness test results when compared to that of the laboratory instruments, providing vital feedback on the progress of the filtration process.
Glycol fluid cleanliness is critical to ensure offshore installations that are free of contaminations. With the help of HIAC GlyCount combined with best practices in sample handling and preparation, it is possible to save monitoring time efficiently, improving the reproducibility of the analysis results.
About Beckman Coulter, Inc. - Particle Characterization
Introduced in the mid-1950s, the Coulter Principle became the foundation of an industry responding to the need for automated cell-counting instruments. The industry developed in three acts, as Wallace H. Coulter and his brother Joseph R. Coulter, Jr., developed the simple idea of passing cells through a sensing aperture.
In Act I, Wallace’s desire to automate the routine erythrocyte count led to a simple idea, the definition of the Coulter Principle, its patenting, its acceptance by the National Institutes of Health, and its description at a national conference.
In Act II, the Coulter brothers addressed the practicalities of a commercial instrument and of a business organization to support its manufacture and sale.
In Act III, a broad research effort developed regarding volumetric errors originating in functional characteristics of the sensing aperture, and the brothers’ growing organization found solutions permitting introduction of increasingly automated hematology analyzers. Today the industry thrives, with several participants.
Beckman Coulter offers a range of particle characterization tools including:
- Laser diffraction particle size analyzers
- Multisizer™ COULTER COUNTER®
- Zeta potential and submicron particle size analyzer
- Surface area and pore size analyzer
This information has been sourced, reviewed and adapted from materials provided by Beckman Coulter, Inc. - Particle Characterization.
For more information on this source, please visit Beckman Coulter, Inc. - Particle Characterization.