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Hydraulic Fracturing Techbook 2018

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EPmag.com | August 2018 | 45 SPONSORED CONTENT includes two months' downtime –lost opportunity cost – plus premature cost of a replacement fluid end. Kerr Pumps' Transfer the Wear™ design philoso- phy inspired its patented Super Seal technology with removable stuffing box sleeve in the packing bore. If packing-bore washout occurs with a Frac 1 CON- NECT™ fluid end, washout transfers to an $800 sacrificial sleeve that can be changed in the field if necessary. No material downtime alleviates need for a redundant fluid end. Seat-deck Washout The next most common and often life-ending fail- ure mode is valve "seat-deck washout" at the lower suction valve seat deck. This begins with valves' con- stant high force hammering onto seats at the strike- face. The OD of the metal-to-metal strike-face is near directly aligned above the landing deck circumfer- ence for the seat (on the fluid end), so a radial shear point can start. Under the right random conditions, this shear point weakens and allows high-pressure fluid to jet through the seat to create seat-deck wash- out failure. As in packing-bore washout, this area can sometimes be weld-repaired for similar $5,000 cost. This requires two service technicians for two, 2 hour fluid end swings, and a replacement fluid end for two months out-of-service downtime. Kerr Pumps' answer to seat-deck washout is its patent pending Super Seat™ design. It eliminates the shoulder and almost any possibility of seat-deck wash- out. A tungsten carbide ring at the metal-to-metal strike-face withstands the valve's high force pounding. Through seven months field testing, the Super Seat™ design eliminated seat-deck washout. There were no weld repair costs or out-of-service downtime, nor need for replacement fluid ends. Suction-Cap Thread Cracking, Face Peeling and Seizing Transition to stainless steel fluid ends slowly extended operating life and revealed the next weak- est link in the chain: thread cracking / face peeling on the front suction side. Thread cracking results as suction retaining nuts back-out ever so slightly and begin pulsating with plunger pumping. Threads are inherently machined stress risers. Tiny fractures can form along the second or third thread from the front on the cap and inside the front suction bore. Face peeling is when that superficial crack occurs inside a suction bore, then propagates outward to the fluid end's front surface, producing a visible circular fissure around the weakened bore. This failure mode usually does not occur until 500-600 pumping hours, but it is a catastrophic fatigue fail- ure. It immediately removes a fluid end from service and requires a new replacement. One cannot exaggerate how punishing duty-cycles affect frac-pump systems. As frustrating as thread cracking and face peeling can be, imagine another extreme situation when a front side cover cap is com- pletely seized in the bore! This can happen when cracked threads cross paths or foreign debris becomes impregnated on opposing thread faces from the load created with each plunger stroke. Kerr Pumps engineers conducted a root cause failure analysis of this increasingly problematic sce- nario. Their findings proved over 287,000 pounds of cyclic load can be forced upon a retainer nut with a 4.50" plunger when pumping at 12,000 psi. Such a pressure load would require 19,404 lb-ft of torque on the cap to overcome that cyclic stress. Add galling plus wear and tear on fluid-end and retainer-nut threads. Result? Regular thread cracking. Thread cracking/ Face peeling TABLE 2: EXTENDED OPERATING LIFE COST COMPARISON Packing Bore Washout at 600 hours Legacy F1C Fluid End Washout Weld Repair Cost $5,000 Replacement Fluid End Cost $62,000 (while original out for weld repair) Replacement Sleeve $800 Service Technician Cost $800 $400 Total Legacy Replacement FE or F1C Repair $67,800 $1,200 6 Month Total (table 1) $82,800 $56,535 6 Month Maintenance, Repair $150,600 $57,735 Savings and Replacement FE Total 62%

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