When selecting a swivel, it’s good to start with a review of its design features and the history of the swivel manufacturer. Some swivels on the market are relatively unchanged over the decades, while others incorporate changes, including the use of more modern seal materials and profiles. Main design features to consider include:
• Bearing configurations and fits specifically designed to absorb loads associated with HDD, including quality sourced spherical roller bearings designed for tensile load, long life and high reliability, and additional bearings designed to support bending loads
• A multi-stage sealing system intended for harsh environments that include drilling fluids such as bentonite
• A high, 5:1 safety factor that ensured a long life for all the mechanical parts
• Internal design features which protect seals from damage that could otherwise be caused by excessive grease pressure during greasing
These are all factors you should consider when selecting a swivel. With cost, like most products, you usually get what you pay for. “You can’t afford to buy cheap,” since poor quality products often will break earlier and end up costing more to replace in the long run. Look for swivels with high-quality bearings from well-established bearing manufacturers and the right type of bearing for the job such as one that will support some side load. And when it comes to bearings, size does matter. Don’t be fooled by swivels in smaller packages, because a reduction in size almost always means a reduction in capacity. Also, when considering size, always buy a swivel that is rated higher than the machine you intend to use it on. Got a 30,000-lb rig? Get a 40,000-lb swivel. The difference in swivel price will be lost in the benefits you will derive. Here is a simple rule of thumb: Use a swivel at 10 percent above its rated capacity and you will decrease bearing life by 25 percent. Use a swivel at 10 percent below its rated capacity and you will increase bearing life by 40 percent.
Sealing is the next most important design feature of your swivel, since they are there to protect the most expensive and important part of your investment, the bearings. Multiple sealing systems are always a good idea since a backup seal could save your bearings and avoid a complete rebuild the next time your swivel is in for service. Look for sealing systems specifically intended for HDD applications. Also make sure it fits your operating conditions, since there are a few things you could do to destroy a perfectly good seal, such as too high of a fluid pressure (which can also occur by going deeper underground), too high RPM, or exposure to chemicals that could degrade the seal. These are all parameters that the manufacturer should be able to assist with.
Finally, your focus is on all the mechanical parts — the size and structure of the clevis pins, the thickness of the lugs, the types of steel used and the manufacturer’s warranty to back it up. The manufacturer should keep records of each swivel including material traceability.
Like any piece of machinery, your swivel does you no good sitting in the yard rusting away. Keep it in clean and in working condition at all times. At the end of each pull, preferably before you remove it from the pipe string, continue rotation and hose down the swivel — pay particular attention to hosing around the gap in the swivel. This is where mud will accumulate and if left to dry out, can do severe damage to the rubber seals. Once the mud dries out, it will lock the seal parts together. Then when you start up again in a week or two, there is a real danger that seal will get torn and be rendered useless. So, wash the seal area until clean water runs out, then add a squirt of oil to keep things moist. Once back at the yard, pump a little grease into the swivel to ensure the bearings remain packed. On many swivels, the grease can flow easily out through the gap between the swivel halves. On these swivels, it is advisable to really pump the grease through to ensure that any contaminants inside the swivel are flushed out. If in doubt, the seal cover may be removed to inspect and fully clean the primary mechanical seal.
On some swivels, grease cannot exit past the seals and must therefore exit through a relief valve. Always make sure the valve is open and clear while greasing. Failure of grease to exit through the relief valve may mean the valve is faulty or no longer operational. Consult the manual and replace it. If grease escapes from the split line groove, this is an indication that the mechanical seal is worn or damaged. Ensure the seal is replaced before its next use.
Ensure that there is no ‘loose’ feeling when the swivel is rotating — listen for grinding sounds which may mean the bearings have become contaminated. Check the clevis pins for wear such as fretting or bending, and be sure to check the clevis lugs around the pins for gouges or other damage. The bearings can be fully replaced if required; some manufacturers offer service kits for most swivel sizes which include a full set of bearings, seals, and hardware such as o-rings and grease fittings. Replacing bearings may require specialized equipment including a breakout tool to unscrew the cap, so consider sending your swivel to the manufacturer or an authorized repair facility for service.
New Designs and Direction
The swivel is one part of the string that you should never take a chance with. Be sure it is in good working condition and that it is suitably sized for both the machine and the pullback. In the past few years alone, many new swivels have come onto the market including auger boring (compression) swivels, thru-bore swivels that allow the passage of drilling fluid through the center of the swivel, locking swivels that can be unlocked in-situ, and high-pressure and marine swivels. Be sure do the necessary research up front to find a swivel that best suits your application.
Chris Pudlak, P.Eng., is engineering/project manager at DCD Design & Mfg. Ltd.