January 1, 2008As one of the leading manufacturers of HDD pullback swivels, DCD Design & Mfg. Ltd. has been associated with the HDD industry since the early 1990s. Back then, when the industry was really about to explode, there was little knowledge or experience around — we were all learning.
At that time, DCD was manufacturing small line swivels for installing cables into clean, dry ducting. They had a simple bearing and seal construction and were certainly not intended to be used in HDD applications. But they were. When DCD started getting phone calls about its swivels not working, we couldn’t help but wonder what the heck was going on. When we saw the swivels sent back to us, all caked up with dry mud, we finally started to get the picture.
In those early days, many contractors strung two swivels together, just in case one failed. Others were using high-quality swivels designed for overhead lifting — good strength — but no sealing capability. Once the mud got in, the bearings seized up quickly.
One year later, the directional underground boring (DUB) swivel was born. Safeguarded by patents, DCD started a truly exciting time in the company’s history. DCD sold those DUB-Swivels to just about every machine manufacturer around at that time, including Charles Machine Works, CMS, American Augers, Barbco and several others.
The DUB-Swivel was the most superior swivel available and quickly became the standard for the industry and that continues to be the case even today. Its design incorporated bearings to absorb the loads, a multi-stage sealing system that really did keep out the mud and a high, 5:1 safety factor that ensured a long life for all the mechanical parts. The sealing system was so good it required a relief valve in order to be able to grease the swivel.
In those early days, the sizes offered only went up to around 80-ton capacity, but this year DCD has manufactured its first ever 700-ton swivel, as well as half a dozen 500-ton units and many more large swivels all in excess of 100-ton capacity. This is indicative of the many large rigs out there today. While 10 years ago the main focus was on building the fiber-optic highway around the United States mostly using the smaller rigs, today’s projects are much more varied and most manufacturers are now building rigs up to 200,000 lbs capacity and even larger.
Projects today include water mains, sewer pipes and so on — all requiring rigs with more power and larger swivels. While over the last decade the design of the swivel itself remains unchanged, much larger capacities are now available.
Buying that Swivel
The main issues with swivels are cost and maintenance. With cost, like most products, you tend to get what you pay for. Learn about the product before spending your money. Why is it as big as it is? The competition may offer a swivel with similar capacity but much smaller in diameter. Ask yourself how can that be — the key component in deciding the swivel’s size are the bearings that are going to take the load. If the other swivel is smaller, then so are the bearings. Find out what type of bearings are used. Typically, a spherical roller bearing is the best type of bearing for absorbing tensile loads. Unfortunately, these are large bearings that cost a lot of money. The upside is that they also last a long time and are proven reliable. If your swivel is to be fixed onto the reamer or drill pipe at the leading end (as opposed to having a clevis attachment that allows it to flex at both ends), then the bearings will undergo much higher side loads. Spherical bearings are not designed to take side loads so how does the swivel handle that? These are good questions to get answered before making your decision.
The sealing system is also important. The life of the bearings is directly related to how well they are maintained. The intent of seals is to keep all foreign matter from getting into the bearings. A progressive sealing system (gradually getting finer and finer) is usually the best. There are high-quality seals available but they can cost well in excess of $1,000 on the larger swivels. Are they worth it? Well, the bearings they are protecting can cost several thousands — so, yes they are.
Finally, look at all the mechanical parts — the size and structure of the clevis pins, the thickness of the lugs, the types of steel used and don’t forget to check the manufacturer’s warranty. Does the manufacturer keep records of each swivel? Do they offer material traceability in the event of failure? Are they reputable? All of the above are valid questions.
One very important tip — 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: Utilize 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.
Once you have decided on which swivel to buy, you now have to figure out how to keep it operational. Like any piece of machinery, it 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.
On the DUB-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.
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 and be sure to check the clevis lugs around the pins for gouges or other damage.
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.
David Clifton is vice president and general manager of DCD Design & Mfg. Ltd., which is based in Richmond, British Columbia, Canada.