MUD PUMP LINERS made of zirco-nia ceramic can offer lifetime cost sav-ings, significantly longer service, betterperformance and safer operation thansleeves made of more commonly usedchrome iron or alumina ceramic,according to data developed by manu-facturers.

P I S T O N W E A R

The special hardness and exceptionalwear resistance of zirconia translatesinto longer service from the urethaneand rubber pistons that move at highspeeds and under tremendous pressureinside the mud pump liners. With truebores and zirconia liners honed to a fine4 RMS finish, piston wear/consumptioncan be reduced by as much as 75%,according to Carpenter AdvancedCeramics (CAC) and C&C EquipmentSpecialists.

Comparative costs of normal averagepiston replacement are dependent uponreplacement frequency. All pistons costthe same, about $125 each, however, thecost gaps widen with the differences inreplacement frequency.

Pistons used inside chrome iron linershad to be replaced twice a month forthree years, for a total cost of $9,000.Pistons inside the alumina liners werechanged once a month, or 36 times inthree years, at a cost of $4,500. Pistonsstroking inside zirconia liners had to bereplaced only 12 times in three years, ata cost of $1,500.

Self aligning rods are either recom-mended or required with aluminaceramic liners. Self aligning rods areused to assure that pistons run perfect-ly straight inside the pump. Imperfectalignment could result in a side load, forexample, that could cause a crack.

The choice of alumina for a mud pumpliner adds a one-time cost of about$1,000 per cylinder, and represents thedifference between higher-cost, selfaligning rods and the lower-cost, stan-dard rods that suffice with both chromeliners and zirconia liners.

L A B O R A N D R I G D O W N T I M E

The costs mentioned above do notinclude labor or rig downtime costs,which are expended numerous times asparts or equipment replacement areneeded. The costs cannot be forecast inevent of breakdowns, emergencies orthat are mud pump liner-related.

Steve N Thompson, CAC Manager/Oil& Gas, recognizes that rig supervisorsare best equipped to estimate costs forparts and components replacement byapplying prevailing hourly labor ratesand hourly cost of lost productivity frompump or rig downtime.

“If it takes two hours of skilled labor tobreak down a pump, remove and replacethe liner, then re-assemble the pump,”Mr Thompson said, “that process couldbe very costly in three years of routineoperation for a platform running two tofour triplex pumps.

“Factor in a surprise or two, a seriousaccident, or multiply by a fleet of 50 to100 drill rigs and you are looking at anexpense that could run into hundreds ofthousands of dollars.”

O T H E R C O N S I D E R A T I O N S

All drilling operations require a plentifuland continuous flow of water to mini-mize heat build up that could burn uppistons and/or cause bore wear. Use of azirconia liner does not require any alter-ation of the driller’s existing lubricationsystem, unlike an alumina liner thatrequires a larger water supply.

If the contractor’s water system is mar-ginal, a change in piping or a water sys-tem re-design may be needed at an

expense of possibly tens of thousands ofdollars.

Safety is enhanced on drilling rigs whenliners are made of zirconia because thecrew is spending less time repairingmud pumps. That is especially impor-tant on offshore rigs where space is lim-ited and environmental conditions suchas wind, rain, snow and a pitching plat-form can make such work hazardous.

Mud pump liners have to withstandsevere operating conditions duringdrilling operations. They circulate up to200 gpm of water and slurry at pumppressures as high as 7,500 psi.. The cir-culated mud contains a large volume ofabrasive, corrosive contaminants. Lostcirculation material containing peanut-like cedar fiber particles is very abra-sive. Further, temperature of slurryreturned to the pump can increase inthe range of 88°C-149°C (190°F-300°F)as drilling penetrates deeper, makingthe mud mixture even more abrasiveand corrosive.

Mud pumps in some rigs operating inthe mining industry have to deal with amixture of salt water and sand, which isboth corrosive and abrasive. In one min-

ing installation, the drilling contractorreported increasing the service life ofhis mud pump liners from 100 days tomore than one year by switching fromthe traditional chrome iron to the newerzirconia ceramic. n

Zirconia mud pump liners offer longer service life

Zirconia mud pump liners come in a variety ofsizes and wall thicknesses.

A piston hull with a zirconia ceramic sleevethat fits inside the piston.

September/October 2004 D R I L L I N G C O N T R A C T O R 45