With tubing strings getting longer and heavier, and specialty tubing getting slicker and more expensive, new gripping technology is needed to hold on tight without damaging the pipe.

Conventional power tong gripping systems rely on toothed metal inserts that penetrate into the tubular surface to obtain sufficient gripping force to produce the high torque required during makeup of the connection. The marks and localized work hardening caused by this penetration accelerate corrosion. That is why tubular failures frequently occur at these locations.
Corrosion-resistant alloy (CRA) pipe is particularly susceptible to cold working and galling. The effectiveness of chrome tubing is reduced considerably if it gets even a small mark or "hot spot" in the assembly process, so it has to be handled gently. What's worse, some 13Cr tubulars have a black, smooth scale surface on the outside, making them slippery and hard to grip. The hardness of this mill scale can be as high as 64 Rc, and even gripping elements specially made for CRA tubulars are only slightly harder than this. Consequently, a number of new gripping technologies have been introduced to hold the pipe tightly without sinking teeth into the metal.
Tungsten carbide
Conforma Clad of New Albany, Ind., has developed a line of tungsten carbide-clad gripper pads, which were introduced in May at the Offshore Technology Conference in Houston. Utilizing the company's expertise in brazing tungsten carbide, the gripper pads come in both carbon steel and heat-treatable, low-alloy steel (type 4140). They come in various flat-plate and semi-circle designs for use with different makes and models of hydraulic power tongs.
The new gripper pads' superior holding force is a result of thousands of sharp contact points made possible by the tungsten carbide that is bonded to the steel substrate. The super-tough metallic sandpaper surface combines material hardness (70-73 Rc) with holding power. Conforma Clad's radial bearings for directional drilling use similar tungsten carbide cladding, and these have exhibited impressive wear resistance in the field.
Better gripping ability means less force is required to hold the pipe, so there is less damage to the exterior surface of the tubulars. This can be critical in applications where anti-corrosive coated pipe is needed.
Fluid Grip
Fluid Grip, developed by research engineers at Frank's Casing Crew, is another technological advance that solves the problem of power tong die marks. Fluid Grip provides a tubing tong that will make up tubular connections with absolutely no damage to the tube body, completely eliminating stress concentrations in the tube body from typical power tong dies. The revolutionized gripping approach is to encircle the tubing with fluid pressure. The gripping surface is completely non-metallic, thereby eliminating any possible marking of the surface. Also, because the pipe is completely encircled, pressure is applied uniformly to the entire circumference regardless of ovality, pipe diameter or surface finish.
Spider with Micro-Grip
Weatherford uses Micro-Grip inserts with its new Vario Compact Spider/Elevator, which can be operated using air or hydraulics to hold tubulars with up to 40 tons of force. The Micro-Grip inserts use serrated vertical gripping bars embedded in an elastomer to distribute the required load equally onto a large number of small peaks, thereby minimizing the indentation of each single peak and preserving the surface integrity of the pipe. The radial force compresses the elastic material, which in turn distributes the force equally onto all the gripping bars, even if the pipe shows some ovality.
"Friction-based systems only provide a limited torque capacity, especially when the pipe surface is wet or greasy," said Holger Kinzel, technical services manager at Weatherford Oil Tool GmbH in Langenhagen, Germany. Super and Hyper 13Cr alloys have been prone to slipping when using the Micro-Grip, but by using a low-friction lubricant on the wedge system between the back of the slip and the spider body, and by cleaning the Micro-Grip slips with a steel brush, such slippage can be virtually eliminated. Using the spider in hydraulic mode rather than pneumatic mode also increased the downward load applied to the slips to 40 tons, which helped get a firm grip on even the Super and Hyper 13Cr strings.
Gripping fiberglass
Bilco's FiberGrip tongs can be used on fiberglass-reinforced plastic (FRP) tubulars or API steel tubulars that have been coated externally with FRP or other corrosion-resistant materials.
A nylon belt gripping system that covers 95% of the tube body allows the tong to grip even non-API outside diameters without damaging the FRP or coatings. FiberGrip can easily accommodate the very low torque required for FRP tubing makeup as well as the high torque required for breakout.
A variety of FiberGrip tongs are available for outside diameter (OD) sizes 23/8 in. through 14 in.
Three jaws are better than one
BJ Services developed the Chromemaster system to avoid teeth marks in 13Cr tubulars. This fully integrated package offers both handling and makeup without leaving die marks that encourage corrosion and can lead to localized weakening and degrading of the pipe's burst and collapse strength.
Made for power tongs, spiders, elevators, slips and bucking units, the system's unique three-jaw sliding-head system ensures correct pipe alignment while wrapping around the pipe to distribute the load evenly, reducing ovality.
Conventional carbon steel dies used on tongs and elevators may leave marks up to 0.040-in. deep in the pipe. Marks left by the tungsten carbide-coated Chromemaster are much less, and many times will be less than the average surface roughness of the pipe.
The high coefficient of friction for the coating (>0.6) ensures that safe gripping is consistently achieved, even on coated tubulars.

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