How compression fittings can optimize oil and gas asset performance
Alternate fitting technology can bring new efficiency to critical oil and gas assets versus traditional cone and thread connections
Critical, medium-pressure oil and gas applications have long relied on cone and thread fittings for safe and reliable fluid system performance. When outfitted with antivibration glands and installed by knowledgeable professionals, these traditional components can provide the performance required. However, in many of today's high-stakes oil and gas operations, these circumstances aren't always so simple.
Cone and thread fittings require careful, time-consuming installation at every connection point. Without skilled technicians who are closely familiar with the cone and thread installation process and the needed time it takes to perform proper installations, each of these connection points has the potential to leak earlier than anticipated, leading to downtime and maintenance.
Unanticipated leaks can have major consequences, especially in today's environment. Oil and gas asset owners and operators are faced with increasingly stringent regulations to ensure safety and environmental compliance, faster turnaround times, and higher expectations for cost containment and operational efficiency. Medium-pressure fluid system connection points represent one area of opportunity to balance each of these needs more effectively.
Today, newer compression fittings are widely compatible in a variety of topside systems, including assets like chemical injection skids, wellhead control panels, umbilical termination units, hydraulic power units, and more. Installation is dramatically faster, while maintainability over the lifetime of the asset can be improved.
To help operators of oil and gas assets understand the benefits they can obtain by switching from cone and thread fittings to compression fittings, this article will explore the key differences between the two types, including their installation procedures and long-term performance.
A faster and more convenient installation process is one major benefit of compression fittings. A few key attributes make this possible:
Fewer Tools Required. Compression fittings require just a standard wrench and vise for a successful installation. By contrast, cone and thread fittings necessitate the use of specialized coning and threading tools, along with a lubricant required to reduce friction during the cutting process. See Figure 1.
A Faster Installation Process. Using coning and threading tools, an installer must properly cone and thread the tube before it is joined with the fitting. Installers must take care to avoid burrs, gouges, or scratches during the coning and threading process; any of these defects can interfere with reliable operation. Once the proper preparation is complete, a collar must be threaded onto the tubing, and a gland nut is inserted into the fitting body for final tightening.
By comparison, compression fittings are installed by threading a preassembled cartridge (which can include a nut, two ferrules, and a plastic arbor) onto the fitting body. See Figure 2. The tubing is inserted and marked to confirm proper depth, and one full turn is applied to complete the connection. (An alternate assembly method using torque to assemble the FK fitting is also available). After checking with a gap inspection gauge, the fitting is complete and ready for use.
Contamination Concerns Eliminated. Between the metallic shavings generated by the coning and threading process and the required use of cutting lubricants, cone and thread assembly can become a messy job. Any excess residue can lead to a potential slip risk, while contamination from metal shavings risks harming system performance. Compression fittings eliminate the need for coning, threading, and the use of a cutting lubricant, thereby alleviating each of these concerns.
These attributes can be helpful in eliminating time and labor from the connection installation process, freeing up staff to focus on other important tasks and leading to significant savings.
For a clearer illustration of the benefits, consider this example: completing a medium-pressure skid package for an offshore oil and gas topside application in which one trained installer will make up each of the skid's 500 connections. Assume the skid uses 316 stainless steel tubing and fittings and that completing a compression fitting connection takes four minutes from start to finish (real-world completion time depends on tubing diameter, material type, and the installer's skill level). Comparably, preparing a cone and thread fitting would likely take up to five times longer, or about 20 minutes.
The time and labour savings here are clear: The total time to complete the skid's 500 fitting connections with compression fittings - specifically Swagelok FK Series Medium-Pressure tube fittings in this example - is approximately 2,000 minutes (33.3 hours) compared to 10,000 minutes (166.7 hours) for cone and thread fittings. The result is dramatically reduced production time for an asset, which can benefit any manufacturer. See Figure 3 for a visual breakdown of the time savings.
More Reliable, Maintainable Connections
Cone and thread fittings, outfitted with antivibration glands, nuts, and collars, can and have historically provided reliable, long-term performance when installed by experienced and skilled technicians. But there are many variables to consider, including the specification of supplemental components and the skill levels of technicians.
By comparison, compression fittings do away with many of these variables. They help eliminate manual installation errors with their preassembled cartridge design. They are also more likely to maintain leak-tight performance throughout their lifetimes without the need for specialized supplemental componentry.
Cone and thread fittings are also prone to loosening over time, even when installed by experienced professionals. It's also estimated that in a typical topside installation, about 20% of cone and thread connections will require tightening or rework during initial assembly and pressure testing. Manual tightening can typically restore a leak-tight connection, but the additional maintenance time required can add up across hundreds of different fittings. And if rework is required, reassembly can be time-consuming and difficult to perform consistently. By contrast, the double ferrule design used for compression fittings reduces the likelihood of fittings backing off when regular system vibration occurs. In addition, compression fittings often require little to no rework due to their simplified installation procedures and the convenience of being able to verify the tightness of connections by using a gap gauge tool.
A final design difference between cone and thread and compression fittings involves the cone and thread fitting's weep hole. The weep hole can act as an accumulation site for unwanted residue and contamination. This can be problematic if used in harsh offshore marine environments in which chlorides can initiate corrosion. By contrast, the compression fitting has no weep hole.
Overall, it is worth considering the benefits that compression-style fittings can bring to the assembly and manufacturing process of critical topside oil and gas assets. FK Series tube fittings, for instance, incorporate a visual confirmation of ferrule presence and facilitate easy and proper installation into the body. The fittings' simple two-piece design consists of a fitting body and a preassembled cartridge containing the nut and front and back ferrules on a disposable plastic arbor. This preassembled cartridge ensures installers use the correct ferrule orientation - error proofing the assembly process.
By helping to reduce installation time, lower assembly and maintenance costs, and deliver long-term reliable connections, FK Series fittings can help asset owners save thousands on a given project compared to using traditional cone and thread fittings.
To learn more about the benefits of compression fittings, work with a reliable supplier that can help evaluate specific application needs and also identify areas of new opportunity to drive down costs and enable safer, more dependable operation.