Mike Foster
Seal Applications Engineer
Bal Seal Engineering, Inc.
Foothill Ranch, Calif.
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| The LKS is a high-PV (pressure/velocity) seal from Bal Seal Engineering, Inc. It combines material and design technology to provide longer service life in tough oilfield applications. |
Just like millions of other kids growing up during the mid-1970s heyday of Saturday morning cartoons, I used to watch an animated series called Super Friends. Glued to the tube, bowl of cereal in hand, I’d marvel as Superman, Batman, Wonder Woman and a veritable A-list of other superheroes joined together and focused their unique powers on a problem that threatened to destroy the planet. If you were a fan, you already know that they always emerged victorious.
By today’s standards, my beloved childhood cartoon seems low-tech and dated. But its underlying message still rings true: when you combine the best characteristics of individual constituents, you can often achieve amazing things.
As a grown-up applications engineer, I frequently apply the same basic principle in my work. That is, when I’m faced with the challenge of sealing critical gear used in upstream oilfield processes, I don’t always consider a single material or configuration. Instead, I think about how I can combine the properties of each to create a solution that’s greater than the sum of its parts.
If you’re designing for today’s hotter, faster oilfield equipment applications, this approach may work for you, too.
Changing times, changing needs
Like television and the rest of the technology landscape, the oilfield industry has experienced sweeping changes over the past 25 years. Market conditions, coupled with advances in the quality and performance of pumps, drives, steerables and other equipment, have resulted in exploration and production practices that are far more aggressive and extreme. Today’s contractors, for instance, are pushing deeper into wells and seeking a much higher rate of penetration. Wash pipe swivels, once considered peaked at 120 RPM and 3,700 PSI, now regularly run at 200 RPM, between 5,000-7,000 PSI. Well bore diameters have been boosted from three to four inches, and mud volume has increased exponentially.
This new frontier of higher temperatures, pressures and speeds is placing unprecedented demands on the design engineer whose job it is to protect expensive motors, sensitive electronics and other critical internal components. It’s also forcing a more careful evaluation and, in many instances, a serious rethinking of traditional equipment sealing methodologies.
The perfection myth
Before we explore a few of the benefits and pitfalls of popular sealing options in different applications, it’s important to note that there’s really no such thing as the “perfect seal.” More specifically, there’s no single material and/or configuration that will solve a sealing challenge one hundred percent of the time.
Similarly, in oilfield environments where seals commonly encounter drilling mud, sour gas, pressures up to 22,500 PSI and temperatures in excess of 350°F, the goal can’t be infinite service life and zero failure; such a target just isn’t realistic. Instead, the focus must be on improving seal reliability and predictability. These are the key factors that make one solution better than another. Achieve both, and you’ll ultimately be able to offer products that give your customers better value, more uptime and more productivity.
The equipment/solution equation
While change has been a constant in the oilfield industry, changes in oilfield equipment sealing really haven’t. In fact, many of the same seal materials and types have been in use for generations. Here’s a snapshot of five widely-used solutions, along with the applications in which you’ll most typically find them. Consult the table (right?) for a breakdown of general benefits and uses.
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| The LKS seal uses graphite-reinforced PTFE, PEEK, a spring, and a ring to provide extended service life in high pressure, high velocity rotary applications. |
• O-ring - Typically the first line of sealing defense, the O-ring seal works well in valves, LWD and MWD tooling and rotary steerables. It’s a relatively inexpensive, readily available seal type that’s easy to install. However, it offers only limited chemical compatibility and, depending on material type, can have very narrow operating temperature and pressure ranges, making it susceptible to explosive decompression. The O-ring can, in some cases, exhibit high “stiction” and high/ inconsistent friction, causing it to bond to some hardware
• Compression packing – The seal type of choice for many progressive cavity pumps, mud pumps/plunger pumps/triflex pumps, valves, wash pipe swivels and down-hole tools, the compression packing’s biggest strength is its ability to serve as an inexpensive, off the shelf solution. Unfortunately, it must also be constantly maintained and tightened until, at some point, it begins to leak. Chemical compatibility is also an issue with this seal, as the elastomer or braided material must be carefully paired with the sealed media. Compression packing is widely considered a fast, fairly effective fix, but it can pose problems when used in a piece of equipment that’s difficult to access and maintain
• Spring-energized U-cup seal (elastomeric) - A seal type commonly found in rotary steerables, mud pumps, piston pumps and control valves, the elastomeric U-Cup is moderately expensive and readily available. It offers good chemical resistance, but has significant pressure and temperature limitations
• Spring-energized engineered plastic/PTFE - Ideal for use in valves, LWD and MWD tooling and rotary steerables, the spring-energized PTFE seal can basically be used anywhere an elastomeric ring or packing would go, but it’s not as readily available or easily installed. It is chemically inert, and it offers higher temperature and pressure capabilities, low/controlled friction. This seal type is typically considered moderate in cost, as it’s usually machined to order. However, some OEMs leverage its chemical compatibility to realize inventory savings by using a single part number for sealing more than one type of media (water, air and oil, for instance)
• Mechanical face seal – This seal’s ability to perform in high pressure and high velocity makes it generally regarded as the standard for pumps, wash pipe swivels and other high pressure/high velocity equipment applications. It offers good temperature resistance and chemical compatibility, too. However, performance can be costly; the mechanical face seal comes at a premium price. It also requires extremely tight tolerances and a means of continuous lubrication to work properly
Better together
Although they’ve been around for a while, the preceding seal types continue to deliver acceptable performance in many oilfield applications, as long as hardware, surface finish, material selection and other factors are properly addressed. However, today’s creeping pressures and accelerated speeds can occasionally prove too much for them. The result can be unexpected failure, productivity loss and, in some cases, serious environmental impact.
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| Select chart to enlarge. |
In light of this fact, a growing number of oilfield design engineers are evaluating the benefits of a multi-component approach to sealing. Borrowing a page from the Super Friends playbook, this approach leverages the unique properties of several materials and seal configurations to deliver better reliability and predictability.
The concept isn’t exactly a new one. Seal manufacturers have been combining elastomers, polymers, even organic materials, for decades. But recent advances in material formulation, design and machining technology have produced a new breed of seal that can take all the heat, pressure and speed some oilfield applications can dish out – and then some.
One example of just such an innovative amalgam can be found in the LKS Seal, which debuted at last year’s Offshore Technology Conference in Houston. The seal, produced by Bal Seal Engineering, Inc., consists of a spring-energized, graphite-reinforced PTFE sealing ring coupled with a high-temperature engineered thermoplastic anti-extrusion element and a metal locking ring.
When you look at the LKS, it’s instantly apparent that each of the components has its own unique role to play: The metal locking ring prevents outer diameter of the seal from dynamic movement, minimizes friction/heat and prolongs seal service life. At moderate speeds, the graphite-reinforced sealing ring retains the ability to seal in high-temperature, high pressure service conditions while providing a high level of extrusion resistance due to its long-wearing properties and built-in lubricity. The thermoplastic anti-extrusion element minimizes seal jacket extrusion, provides longer sealing life, forces wear to occur at lip contact area (not the hinge point), and extends seal performance range at low and high temperatures (-94° to +550°F). And the Hastelloy Canted-coil spring exerts uniform sealing force against the shaft, reducing heat build-up and extending seal life while providing excellent corrosion resistance and chemical compatibility.
The LKS and other similar multi-component seals represent a novel take on problem-solving, because they deal in capabilities rather than limitations. Their design considers, for example, how the high-temperature behavior of PEEK (which becomes more flexible at 180°F) will complement the lubricity of PTFE, and how the force exerted by a spring can help the whole package provide longer service life. You might say it’s sealing from a holistic perspective.
So what’s the bottom line?
Better seal performance equals greater equipment uptime. Uptime translates into greater productivity, and productivity is profit. Conversely, the unexpected failure of one seal can mean hundreds of thousands of dollars in downtime costs – not to mention the potential for some very adverse environmental impact.
As engineers who design for the oilfield, we understand the importance of reliability and predictability. But we also know that no seal will last forever. Traditional sealing types and materials may work for your application, but trends toward higher speeds and pressures may compromise them. Thus, if you can combine the best in materials and design to create a solution that behaves in a very predictable, very reliable way, you can maximize uptime and equipment performance.
If your solution is also easy to install, maintain and replace, you’ll end up looking like a superhero.
For more information on Bal Seal Engineering, visit www.balseal.com.