Hydraulic Fracturing Techbook 2018

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54 | August 2018 | HYDRAULIC FRACTURING: TECHNOLOGY One Connect, a Super Stainless fluid end that addresses many of the failure points in the classic model. "One of the common failures for fluid ends for the longest time, especially when they were made from carbon steel, was cracking at the intersecting bores inside the fluid ends," explained Art Travis, vice pre- sident—Planning & Strategy, at Kerr. "Because of the high tensile and yield strengths of our Super Stainless II material, we were able to all but eliminate intersect- ing bore cracks. From there we kept researching to realize that there are mechanical properties in how you manufacture and how you mill the steel to relieve stresses and to reduce stress risers that are the first areas that tend to crack. We started studying what the best geometries would be inside the fluid end for each size and came up with repeatable manufacturing processes that can be done with the CNC machines that we have, where others would just try to round the edges in their de-burr process. For us, we believed that all but eliminated intersecting bore cracks. That was the big first one." Kerr adopted a design philosophy it called "Trans- fer the Wear," where it transfers the wear to a sacrificial consumable part and away from the expensive fluid end/pressure vessel. The company realized that it could move the wear away from these internal com- ponents that tend to move with the pulsation of the pumping fluid end. "So we put specially located seal glands in the fluid end that hold engineered seals designed to protect the gland of the fluid end as well as the seal. At this point you've transferred the wear from the fluid end to the suction cap," Travis said. "We have a removable stuffing box in our fluid end so we were able to move the wear to it. The stuffing box sleeve is sacrificial in two places. The first is the inside diameter if your packing goes and the second is the outside diameter that seals to a seal housed in a gland in the fluid end on the packing side." Still, other areas needed to be addressed, like thread cracking on the front of the fluid end. The problem was solved by using a cover cap with a patent-pending stud-and-nut system, allowing precision torque to load the fluid end past the cyclic stresses seen and keep the studs in a safer constant state of static load. "Thread cracking has become more prevalent," Travis said. Another area of concern was opposing stresses at the fluid end's flange connec- tion. Kerr opted to eliminate the large flange in favor of a more rigid T1 steel connect plate. The change allowed the company to reduce fluid end flexing by 420%. Eliminating the flange had another benefit. "If you look at an old style flanged fluid end, that is a lot of material," Travis said. "You have to rough out the whole flange, and there is scalloping you have to do so that you can get the nuts to thread onto the stay rods. What we ended up being able to do is get two fluid ends from one forging, which doubled our mate- rial capacity. We were also able to cut our machine time in half. That is how we were able to price it at a low market price. It is the most technologically advanced fluid end at the lowest price. This isn't some fire sale. This is how we've gone to market. It is very disruptive." Kerr's goal with the Frac One Connect is to extend two reliability measures—a longer mean time between maintenance and a longer mean time before failure. The longer mean time before failure equates to a longer operating life, and the company has provided that through the design and inclusion of sacrificial consumables to extend the life, which effectively low- ers the total cost of ownership. "What we offer is time without increasing the price," Travis said. "A longer maintenance interval and to do less maintenance when you have to go into the head, and give it a longer operating life. It is a bit of a departure from the legacy form factor and, of course, we're all creatures of habit and change is difficult. There are more moving parts, but those have allowed us to distribute stresses that reduce or eliminate certain failures." n The Kerr Pumps Frac One Connect fluid end bolts right up to existing stay rods with a more rigid flangeless design. It includes replaceable stuffing box sleeves with all seals embedded into the fluid end to prevent washouts. (Image courtesy of Kerr)

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