Swivels serve an important purpose on the horizontal directional drilling (HDD) jobsite. These durable pieces of tooling connect the drill string to the product pipe and prevent the pipe from twisting during pullback even as the drill string rotates. It is one of those pieces of HDD tooling that every HDD project — from small fiber installs to big inch oil projects — requires.
As is the case in the HDD world. You get what you pay for and less expensive is not always better. To delve into the wonderful world of swivels and offer some tips on maintenance and selection, we spoke with the folks at Century Products Inc., Sharewell HDD BV and Vermeer Corp.
“Being able to rotate the drill string while pulling has two key advantages,” says Sharewell EMEA operations director Dan Billig. “One, the ability to rotate reamers or other tooling which has been placed on the end of the drill string while pulling. These tools maybe there for centralization purposes, or perhaps to provide a final reaming stage while pulling the product pipe. Either way, the ability to rotate while pulling is essential to either allow for this tool to ream (if it’s a reaming tool), clear blockages, lift settled cuttings into the mud flow to keep the hole clean, or just to avoid getting hung up on potential obstructions in the formation.
“Two, to be able to break the static friction on the drill string. Rotating drill pipe has a considerably lower friction when pulling when compared to non-rotating drill pipe. Simply put, if you are rotating your drill pipe, more of the pull force you apply will be transferred to the product pipe.”
On the small side, swivels are available in the 2 to 3 ton pulling range, and then go up to the 550-ton swivels used on the max-rig projects. And there are swivels for every size in between. Before starting a project, the contractor should assess what size swivel they need to get the job done based on the working load rating.
“After deciding what amount of force (pounds) will be needed to pull a product pipe into a hole, then the capacity of the swivel should be disseminated by the rating of the thrust bearing in the swivel,” says Century Products president Todd Bielawa. “Thrust bearings are rated by bearing manufactures for a dynamic (rotating) load. Basically, the larger capacity of the thrust bearing the more load the swivel will handle. A good rule of thumb when comparing swivels is to look at the outside dimension (OD) of the swivel. Typically, larger swivels – 110 ton to 550 ton – have an approximate 1- to 1.5-in. wall thickness in the body. If you double the wall thickness and subtract from the OD, you will determine the largest size thrust bearing that would fit inside the swivel. In short by comparing OD dimensions one can be fairly certain you would be comparing apples to apples.”
Another good rule of thumb when the pull force of a project is near the safe working load rating of the swivel it is best to upsize the swivel.
“Ideally, the size of the swivel — and the optional attachments — should be matched to the product pipe being pulled rather than the rig itself. Larger swivels have a higher rotational friction, so pulling a small product pipe with an oversized swivel can cause downhole rotation of the product pipe during the pipe pull which could cause problems,” says Billig. “An assessment of the ground formation should also take place to determine the best configuration of the swivel and pulling assembly. If gravel is expected care should be taken over the distance from the last drilling tool on the string – if there is a tool in front of the swivel – and the front of the product pipe to avoid gravel falling in between the tool and the product pipe and potentially getting the drill string and the product pipe stuck downhole.”
HDD tooling takes a beating. Swivels are no different, and depending on the size and brand, as well as the type and number of projects a contractor works each year, the lifespans can vary. Even with this variability, there is some commonality from the small projects to the large that will ensure a contractor gets the most out of the tooling. It boils down to proper maintenance.
“Inspect the swivel for wear and cracks, especially around the eyelet/pin area. Confirm the swivel turns freely. If significant structural or functional damage is detected, the swivel must be replaced,” says Jason Zylstra, product manager Lifecyle at Vermeer. “[Also,] properly rig the swivel to drill string to minimize side load forces.”
To that Bielawa adds, “Keep your swivels clean, greased, and if possible, out of the sun to help keep damage to the seal and seal cavities to a minimum. The single most important item to put in your operational due diligence would be to grease the swivel both before and after use with a high pressure, high temperature grease.”
Zylstra adds that the grease should have water resistant properties. And, when greasing after each use, the contractor should grease to purge to help remove debris from the swivel.
“After hard pulls or on a yearly schedule have your swivels disassembled, inspected, and re-assembled by a qualified manufacture that can ascertain whether the bearings and seals need replacing,” Bielawa says.
If bearing wear is suspected, it is important to replace them as soon as possible to avoid potential damage to the shaft and other swivel body parts. Billig agrees with these lifespan and maintenance tips, and adds that with minimal, but regular maintenance, a swivel can last a long time.