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Jerry Johnson was introduced to the oilfield in 1979 when he went to work at TRW Mission in Houston, Texas. For the next ten years he was involved in the designing and field testing of expendable parts for positive displacement pumps. He then spent another ten years with a major oilfield firm designing oilfield products and field testing prototype equipment. Jerry is now employed at National Oilwell Varco in the Mission Products Group. In the 25 years Jerry has been in the oilfield, he has always focused on product design, product application, supporting the sales department and customer to better understand the products and their uses. National Oilwell Varco appreciates the dedication and the passion Jerry has exhibited to put together this document. He provides valuable information allowing the reader to match the proper products to the varying application needs of today’s demanding drilling industry. We wish to express our gratitude for the excellent results contained within. Although some of the material outlined in this guide is basic information, it is hoped that some elements offer some insight into the products, the product application and, where applicable, the product limitations. This guide also attempts to alert the customer to product failure mechanisms and to identify problems so expenses and downtime are reduced. As new products and drilling conditions arise, this guide may be expanded to include those items and any problems that might develop in those conditions.
This reference information is to aid the end user of triplex pumps so that problems can be identified and corrected. This should allow the end user to reduce pump downtime, increase pump parts life and decrease overall operating costs related to the products discussed. This should be applicable to all triplex single acting pumps used in drilling, well service, mining, slurry and other types of fluid transfer. The products to be covered: • Liners (all types) • Pistons (all types) • Valves and Seats (all types) • Backflush Systems • Liner Retention Systems • Gaskets (all types) • Modules (in brief) • Piston Rods (all types) • Piston Rod Clamps In addition to the products discussed, attention will be paid to the more common types of failure mechanisms and the corrective actions to remedy the situation. This will include conditions of higher pressures, temperatures, solids, corrosion and different types of fluid mediums.
General Liner Information Liners should never be struck directly with hammers. If one must hammer to get a liner in, place a piece of wood between the liner and hammer to absorb some shock and eliminate dents in the liner. Dents in the shell material can cause the sleeve or chrome plating to crack. Always remove any rust preventative in a sleeved liner. The rust preventative chemistry may be harmful to the piston material. Grease the liner and piston prior to assembly. Make sure the liner gasket is lightly greased and properly installed. While connecting the liner to the pump, tighten the liner clamp or collar to specification. After a certain amount of time, the liner will seat. This may affect the collar or clamp tightness. To avoid extrusion of the gasket and possible washout of the fluid end, retighten the collar or clamp to specification the next time the pump is down. On bolted collar type connections, the fasteners at the bottom of the collar are difficult to get to. Washouts of both the liner and fluid end can sometimes be attributed to improper torque of the bottom fasteners in these cases. Use of proper tools is critical to allow even torquing of all fasteners.
Ceramic liners are currently the premium liner offered today. Ceramic liners have been known to operate well over the 7,000 hour mark. Due to the high hardness of the ceramic surface, they wear substantially less than other liner types. This translates into longer piston operating times. If the correct conditions are present, the cost per operating hour can be much less than that of the other liner types. The main mode of premature failure of the ceramic liner is caused by the disruption of the ceramic surface in the piston stroke area. This is normally caused by the piston’s metal body coming in hard sliding contact with the ceramic surface. This hard sliding contact may be the result of a misaligned pump or a piston left in operation too long after failure begins. The amount of damage done to the surface in a given amount of time would depend on the degree of misalignment or, in the case of the piston failure, the operating pressure, strokes and fluid temperature. The disruption of the surface is caused by the microscopic fracture of the ceramic material. These fractures are similar to glass fractures and are very abrasive on the mating component (in this case, the piston). The fractured material is also very hard and will remain in place unless the liner is repaired by re-honing the bore, thereby renewing the liner. A liner that has a damaged bore can usually be identified by adiscoloration of a section of the bore and the texture of the bore will not be as smooth as the opposing side. Corrosion, solids content, temperature of the fluid and fluid chemistry have relatively little effect on the ceramic liner. When installing the ceramic liner, care should be taken not to strike the liner with hammers. When installing the piston and rod assembly, care should be taken so that the hanging weight does not cause the piston flange to damage the liner bore. Sometimes, on initial assembly, the ceramic liner bore will be broken in by causing the first piston to wear at a faster rate. After the first piston, the liner is broken in and the piston and liner should provide the end user with a very satisfactory life expectancy.
The Supreme liner is a premium liner with a sleeve of hardened high chrome iron material installed in an alloy or carbon steel shell. This liner has been a premium liner for many years. High chrome iron sleeved liners, while resistant to wear, do not have the hardness of the ceramic liner. Some drilled solids, such as quartz, have a higher hardness than the high chrome iron material. One mode of premature failure is what is referred to as liner streaking. This is caused from the presence of hard drilled solids entrapped between the piston and liner bore. As the piston reciprocates in the liner bore, these solids slowly wear longitudinal grooves in the liner bore. If left unchecked, these grooves will develop to a point where the liner is washcut and destroy the liner. To retard groove growth and to prolong the liner life, it is recommended that every time the pump is stopped (or once a day) the operator should turn the piston / rod assembly approximately ¼ turn. This will disrupt the current wear pattern and start a new one. In this fashion the groove will never achieve the depth to cause awashcut. Solids content of the fluid has a direct relationship to the high chrome iron liner wear rate and its useful life. While misalignment and piston failures do contribute to higher wear rates in the high chrome iron sleeved liners, these conditions do not disrupt the surface of the bore as dramatically as the ceramic liner. The wear rate will be higher than the ceramic, but the surface will not be as damaging to the piston. For this reason, the high chrome iron liners do not have to be renewed. Corrosion, temperature and fluid chemistry normally have little effect on the life of the high chrome iron liner. The high chrome content resists corrosion pitting in most applications where the liners are currently being utilized. Gradual temperature changes have no effect and today’s fluid chemical compositions have no measurable effect in the drilling or mining industry. Care should be taken when installing a high chrome iron sleeved liner that the liner is not hammered in any way during installation.
In some smaller size liners and some liners approaching maximum bore for the pump, liners manufactured with a chrome-plated bore are offered. These liners offer some resistance to abrasion and limited resistance to corrosion. Hard sliding contact such as pump misalignment and a prolonged piston failure can strip the chrome plating from the base substrate causing flaking of the chrome material. Once flaking of the chrome starts, this will continue until failure. This flaking chrome is very abrasive and piston life will be shortened. Chrome plating is inherently porous. Corrosive conditions will undermine the plating and rust the substrate, loosening the chrome plate. It is recommended that, when not in use, the chrome plated bore be kept greased to limit the amount of air and moisture that can come in contact with it. Although chrome plated liners are much better than induction hardened liners in operation, care must be used when operating these liners. Over 90% of the claims sought on chrome plated liners are the result of corrosion or pump misalignment, or due to piston flange drag or failure. Rarely is it defective chrome plating. To avoid damaging the liner, use no hammers on assembly and ensure the hanging weight of the piston / rod assembly does not put stress on the bore.
Induction hardened liners are resistant to abrasion but not generally recommended for triplex pump service. These liners have no designed resistance to corrosion. Since triplex pump liners are open to the atmosphere, corrosive conditions exist in all environments in which the liner will be operating. Once the corrosion pitting develops, piston life will diminish at a rapid rate.
Liners are packaged and coated with paint and rust preventative for short-term covered warehouse storage. Liners exposed to the outside elements and temperature extremes may deteriorate over time. Liners should be kept in the original unopened container away from ground moisture and elevated above concrete floors. Care should also be taken to eliminate conditions that promote condensation in the original container. Keep the liners away from direct sources of moisture. Some liners are packaged with liner gaskets manufactured with elastomeric compounds. Liners with liner gaskets should be stored away from high heat areas. After gaskets are molded, the gasket starts to age at a linear rate. Heat will increase the rate of aging, cooler temperatures will maintain or reduce the rate of aging. The cooler the temperature at which these gaskets can be stored, the longer the gaskets' useful life. The gaskets should also be stored away from direct sunlight (ultraviolet radiation), aromatic solvents, moisture and electric motors (ozone production). At times, used liners are stored short term for later use. The proper storage preparations for storage of used liners should include the cleaning of all surfaces of contaminant matter and inspecting for damaged areas that could be detrimental to the function of the product. If no damaged areas are found, the liner should be coated with clean heavy grease over all surfaces to reduce the possibility of corrosion. Corrosion in the bore will abrade the piston, corrosion in the gasket area will reduce gasket life and corrosion on the outside of the liner may swell the surface causing installation difficulties.
General Piston Information Pistons come in many styles and compositions. Normally a piston of a certain type is designed for a specific purpose. Outside the designed purpose, this piston may not be suitable or economical for use. The brief descriptions below outline some of the designed criteria and limitations of standard piston types. For the optimum performance of a piston, the pump must be properly supercharged, the pump should not have any misalignment issues, the liner should be in good operational order and the backflush system should be properly designed and in good working order. Fluid temperature, solids content, fluid chemistry, operating pressure and pump speed also have a major impact on piston life, but are not normally as controlled as the other criteria. The pump supercharger should be designed to operate properly. It is essential that the pump be continuously flooded and at the correct pressure. If the pump is not properly supercharged, the piston can suck air from behind the piston lip and create a water hammer that causes excessive vibration and destroys the piston. A pump that is only marginally supercharged may not have the pressure to energize the piston on the backstroke. An energized piston on the backstroke helps centralize the piston in the liner and eliminates some flange drag on the liner. The proper supercharging pressure is 80 feet of head at the positive displacement pump. The proper flow of the supercharger would be 1-1/2 times the maximum rated output for the positive displacement pump up to 170 strokes per minute. Over 170 strokes per minute, sizing should be increased to 1-3/4 times the maximum flow of the positive displacement pump. The supercharger should be designed with its own driver to operate at a constant speed regardless of the positive displacement pump speed. Supercharger pumps that are belt driven from the jackshaft of the positive displacement pump do not provide the required pressure at low speeds to fill the cylinders and energize the pistons. This can damage the positive displacement pumps power end and reduce piston life. Pump alignment is a critical issue and will be a major factor in piston and liner life. The degree of misalignment is directly related to the reduction in life of fluid-end expendables. Misalignment is also a direct source of additional frictional heat build-up in the piston and can elevate the temperature at the surface of the piston to very high levels. These levels can easily exceed the maximum rated temperature ratings for the piston. On urethane pistons, it can cause the compound to melt and disintegrate. Urethane pistons will have the visual characteristics of a melted candle. Material will be missing and the surrounding areas of the missing material will be very smooth and sometimes discolored. On black rubber pistons, it can cause the compound to burn on the surface. Once a black rubber piston has reached these elevated temperatures, the rubber will take on a smell of burnt rubber that will remain with that piston. Self-aligning rods are produced to eliminate some misalignment. These can help if the misalignment is mild to moderate but not if the misalignment is severe. In these cases, the pump should be repaired to OEM specifications to reduce expendable costs. The pump backflush system is also another very important factor in piston life. The backflush fluid cools the piston; aids in lubrication and flushes particulate matter from the liner bore. For urethane pistons, the recommended minimum flow to each piston is 14 gallons a minute uninterrupted. For black rubber pistons the minimum flow to each piston is 10 gallons a minute uninterrupted. The backflush nozzle should be attached and positioned so that the entire liner bore is covered as the piston strokes down the liner. This ensures that all areas of the liner bore the piston travels in are cooled, lubricated and flushed. Areas that are not covered will cause high heating of the piston compound. The compound failures will be similar to those outlined in the misaligned pump section above. The cooler and more lubricated the piston is, the longer the piston will operate. Backflush water temperature can also be a factor in piston performance. The cooler the backflush water is, the better the piston performance. To reduce some frictional heat and improve lubricity, some contractors add water-soluble oil to the backflush water mixture. The oil should be water soluble, non-detergent and should be environmentally friendly to the location.
Pistons manufactured using urethane compounds typically fail from one of four different conditions and each can be identified fairly easily. The four conditions are: heat, extrusion, abrasion and chemical attack. Failure can also occur due to multiple conditions. HEAT : Urethane pistons that fail due to heat have a loss of material and acquire a surface similar to a melted candle. This condition can be a result of high fluid temperature, inadequate backflush supply or frictional heat due to other forces. As the temperature increases, the mechanical properties of the urethane decrease. Standard (not high temperature compounds) urethane pistons have a maximum temperature of approximately 180° F (82° C). This maximum temperature is the sum of the temperature of the fluid being pumped plus the frictional heat generated by the reciprocating piston. EXTRUSION : Urethane pistons that fail due to extrusion look torn and are very rough in appearance. They also have a loss of material emanating from the piston flange upward. Edges of the urethane surface will be sharp and rough to the touch. Premature piston failure due to extrusion usually indicates that the liner bore to piston flange gap was too great for the pressure operated. ABRASION : Urethane pistons that fail due to abrasion have loss of material and the surface will be rough but not torn. Longitudinal streaks will normally be observed on these pistons where solids have been entrapped between the urethane compound and the liner and operated for some time. CHEMICAL ATTACK : Urethane pistons that fail due to chemical attack are not as easily identified visually. The urethane compound will soften and sometimes swell. Normally this type of failure will have a heavy chemical smell of solvents or hydrocarbon compounds when first examined out of the pump. The attacking compounds may dissipate shortly after removal and lose this chemical smell shortly thereafter. A few mud bases and mud additives have chemistries that, when first added to the mud, tend to degrade the elastomers. Most of these bases and additives are less volatile over time and as the fluids circulate tend to become diluted to the point that they do not continue to degrade the elastomers. If new bases or additives are added that have not been utilized before it may not be the fault of the elastomers if some fail earlier than normally expected. MULTI-CONDITION : Some failures are caused by more than one condition. Under heat failure conditions, the urethane will eventually be lost to a point where the piston will have what seems to be a blowout. The blowout will take on characteristics of extrusion by the rough edges surrounding the failure. Under extrusion conditions, fluid that fills up the void in the extruded area can hydraulically push the piston to the side opposite of the void in the pressure stroke to cause excessive heating of the urethane at that location. Normally, one can discern between the primary cause and secondary result of the failure.
Black rubber pistons normally fail from one or more of the following conditions: heat, extrusion, abrasion, chemical attack, ID/OD washout or putting rubbers on piston bodies too worn out for the operating pressure. The failures on the black rubber piston are not as easily identified visually as those of the urethane type but can be determined by the following and other identifying characteristics. HEAT : Once the rubber has exceeded a certain temperature, the rubber will take on a smell of burnt rubber. This smell will not go away. Sometimes the outer surface will become charred and hard to the touch. Carbon black may rub off the piston if it has seen very high temperatures. The high temperatures can be aresult of the same mechanisms as the urethane piston. As the operating temperature increases, the mechanical properties of the rubber decrease. For black rubber pistons the maximum operating temperature is 225° F (107° C). This maximum temperature is the sum of the fluid medium being pumped plus the frictional heat generated from reciprocating motion. EXTRUSION : Under extrusion conditions and also while putting rubbers on worn out piston bodies, if the liner is too worn or the rubber is installed on a too worn piston body, the piston rubber fabric will extrude into the gap between the body and liner and be severed. With every stroke more material will extrude into this gap and be severed, leaving a void at the piston rubber / piston body interface. This will continue until the fabric no longer supports the rubber face and the piston lip fails. Visual characteristics include fabric loss, loss of lip material and a rough surface in the rubber lip. In pressures above 2,500 psi, it is not recommended that the customer change piston rubbers on used piston bodies. Beyond this pressure it is not economical to do so because of the reduction in piston rubber life, increased downtime and increased liner wear. The Supreme piston bodies have grooves machined into the piston flange to gage wear. The deep groove is for operating pressures of 0 to 1,500 psi, the shallow groove is for pressures between 1,500 psi and 2,500 psi. If operation is between one of these two pressure ranges, the appropriate wear groove can be used to gage if the piston body can be redressed with another piston rubber kit to renew the piston. If the wear on any part of the piston flange is deeper than the associated wear groove for the operating pressure, the piston body is considered worn out and should not be redressed with another rubber kit. ABRASION : Under abrasive conditions, the black rubber piston will show a loss of material and the loss should be uniform in appearance. The rubber may also have longitudinal streaks in the rubber and fabric where solids have been entrapped and reciprocating under pressure in the liner. CHEMICAL ATTACK : Under chemical attack conditions, the rubber will decrease in hardness and may swell in size depending on the chemical present. The swelling may get to the point where the top of the rubber is cut by the piston end plate. Normally, the piston will smell of solvent base or strong hydrocarbon content. This smell may not last long due to the fact some volatiles evaporate in air. ID/OD WASHOUT: One type of chemical attack involves oil based muds and the aniline point of the base oil. The relative aromatic content of oil is indicated by its aniline point, which is the temperature in degrees Fahrenheit that oil and a chemical called aniline will mix with each other. Oils having a high aromatic content have a low aniline point. Oils having a low aromatic content have a high aniline point. Consequently the high aniline point diesel oils are the most desirable for use in drilling mud as they will cause less difficulty with the elastomers on the rig. Oils having an aniline point of 170° F or above should not cause any difficulty with the elastomers on the rig. Oils having an aniline point of 150° F to 170° F should not cause any great amount of trouble. Oils with aniline points below 150° may cause some problems with elastomers on the rig. The aniline point of oil may not be able to be checked once mixed with the drilling mud, but the supplier of the diesel oil should be able to supply this data prior to purchase. It is often recorded when initially processed. The condition of ID/OD washout is hard to determine visually without disassembly of the piston. This condition, although rare, happens when the seal between the rubber ID and the piston hub OD fails. If there are no visible signs of failure on the outside of the piston, this may be the cause of failure. The cause of the ID/OD wash is normally from installing a piston in a liner too worn for the operating pressure. The rubber tries to deform to the liner ID and in doing so, sometime causes a seal failure in the ID of the rubber.
The Blue Lightning piston was designed and developed primarily for use in ceramic liners for pressures up to 7,500 psi but can also be used in high chrome iron sleeved liners with great success at all pressures. The benefits of the Blue Lightning include the ability to grow to the size of the liner bore in operation and prevent extrusion of the urethane face stock. The specially formulated urethane compound is highly resistant to abrasion, extrusion and tear. The back-up ring on this piston also centralizes the piston in the liner, reduces friction and prevents the transfer of metal to the liner bore when the piston is about to fail or if minor misalignment is present. This increases the ceramic liner life and reduces scoring of the surface. The specially formulated urethane compound is also resistant to the higher temperatures sometimes used in the industry and can normally operate up to 220º F (104º C). The Blue Lightning piston is recommended for systems with oil based mud and synthetic based mud. It is also recommended for water-based muds when weights are 11 lb/gal or over. The Blue Lightning piston is not recommended for clear water or seawater pumping due to the lack of lubricity of these fluids. As in all urethane pistons, the backflush requirement is recommended at 14 gal/min or greater for each piston.
The White Lightning piston was developed to be areplaceable style urethane piston. This piston has the abrasion and tear resistance of urethanes with the ability to change inserts if the operating pressures are below the 2,500 psi threshold. The White Lightning is formulated and processed in such a manner to also resist some fluid chemistries that may affect other urethane compounds. This piston can operate in up to 200º F (93º C) service and is rated for 6,000 psi. The White Lightning piston is recommended for systems with oil based mud and synthetic based mud. It is also recommended for water-based muds when weights are 11 lb/gal or over. The White Lightning piston is not recommended for clear water or seawater pumping due to the lack of lubricity of these fluids. As in all urethane pistons, the backflush requirement is recommended at 14 gal/min or greater for each piston.
The Green Duo piston is a bonded dual durometer piston that is highly resistant to abrasion and tear. The bonded construction resists extrusion under pressure and restricts movement to reduce the build-up of heat. The Green Duo can operate in up to 180º F (82º C) service and has operated at up to 6,300 psi. The Green Duo piston is recommended for systems with oil based mud and synthetic based mud. It is also recommended for water-based muds when weights are 11 lb/gal or over. The Green Duo piston is not recommended for clear water or seawater pumping due to the lack of lubricity of these fluids. As in all urethane pistons, the backflush requirement is recommended at 14 gal/min or greater for each piston.
Supreme pistons are manufactured from an oil resistant Nitrile compound with a cotton fabric back. The face compound is resistant to most chemical compositions that are currently being utilized. The Supreme piston is manufactured for use in both triplex single acting and duplex double acting pumps. The rubber inserts on the Supreme can be changed using a rubber kit, but this is not recommended if operating pressures are over 2,500 psi. Over the 2,500 psi threshold, it becomes cost prohibitive to change inserts due to the increased extrusion of the piston and typical premature failure. The Supreme piston can operate in temperatures up to 225º F (107º C) and can operate in pressures up to 7,500 psi depending on piston size. The Supreme piston is recommended for systems with oil based mud and synthetic based mud. It is also recommended for water-based muds when weights are 11 lb/gal or over. The Supreme piston can be used with clear water and seawater systems with some success. The backflush requirement for the Supreme piston is 10 gal/min or greater for each piston. The Supreme piston bodies have grooves machined into the piston flange to gage wear. The deep groove is for operating pressures of 0 to 1,500 psi, the shallow groove is for pressures between 1,500 psi and 2,500 psi. If operation is between one of these two pressure ranges, the appropriate wear groove can be used to gage if the piston body can be redressed with another piston rubber kit to renew the piston. If the wear on any part of the piston flange is deeper than the associated wear groove for the operating pressure, the piston body is considered worn out and should not be redressed with another rubber kit.
The Regular pistons are manufactured from natural rubber that is highly resistant to abrasion and tear. The piston rubbers are mounted on the same bodies as the Supreme piston to allow piston rubber changes at pressures less than 2,500 psi. The Regular rubber can operate in temperatures up to 180º F (82º C) and can operate at pressures up to 5,000 psi. The Regular rubber is recommended for clear water and seawater service. It can also be utilized for water based mud service especially if the mud weight is below 11 lbs/gal. The Regular rubber should not be used in oil or synthetic based mud systems. The Regular rubber is not as resistant to chemical attack as the other pistons and should not be utilized in chemical base operations. The backflush requirement for the Regular rubber is 10 gal/min or greater for each piston.
The Flex Lip piston is a bonded style piston with a Nitrile face stock. This piston is oil resistant and is compatible with most drilling fluids currently in use. The Flex Lip piston can operate in temperatures up to 210º F (99º C) and can operate up to 4,500 psi. It is manufactured for use in both triplex single acting and duplex double acting pumps. It is also recommended for water-based muds when weights are 11 lb/gal or over. The Flex Lip piston can be used with clear water and seawater systems with some success. The backflush requirement for the Flex Lip piston is 10 gal/min or greater for each piston. The Flex Lip is not recommended for systems with a high concentration of solids.
Pistons and piston rubber kits are packaged and coated with rust preventative for short term covered warehouse storage. Pistons and rubber kits exposed to the outside elements and temperature extremes may deteriorate over time. Pistons and rubber kits should be kept in the original unopened boxes away from ground moisture and elevated from concrete floors. Care should be also taken to eliminate conditions that promote condensation in the original box and to keep the box away from direct sources of moisture. Pistons and piston rubber kits are packaged with sealing elements manufactured with elastomeric compounds. Pistons and rubber kits should be stored away from high heat areas. After the piston’s seal element is molded, the sealing element starts to age at a linear rate. Heat will increase the rate of aging, cooler temperatures will maintain or reduce the rate of aging. The cooler these pistons and rubber kits can be stored, the longer the sealing element’s useful life. The pistons and rubber kits should also be stored away from direct sunlight (ultraviolet radiation), aromatic solvents, moisture and electric motors (ozone production). When stored properly, as described above, the shelf life of black rubber products (Nitrile, Neoprene, etc.) is five years after the date of manufacture. If stored improperly or in conditions with higher heat this shelf life is reduced accordingly. When stored properly, polyurethane products have a shelf life of four years from the date of manufacture. If stored improperly or in conditions of high heat the shelf life is reduced accordingly. Black rubber and polyurethane products should not be used if the actual age exceeds the shelf life. If they have not been stored properly and if they appear milky or cloudy in color or substantially harder than fresher examples, they should not be used.
General Valve and Seat Information Valves and seats come in many different styles and are designed for many different applications. What is referred to as the drilling valve can be used in drilling, mining, fluid transfer and slurry applications. The drilling valve also comes in a variety of configurations such as full open unitized body, full open plate type assembly, and cross-arm style high, medium and low pressure type bodies. Each drilling valve is designed for a particular application but can sometimes be used with great success in other applications. Another valve referred to as a well service valve can also be utilized in mining and fluid transfer. The well service valve is normally of full open design and is either a unitized body or plate style assembly. Some of the drilling and well service valves offer different seal or insert materials for different applications. Some go beyond the traditional polyurethane and Nitrile and offer inserts for acidizing, elevated temperatures and chemical pumping. Normally, for medium to high-pressure applications, the polyurethane insert is the most recommended insert. The polyurethane is specially formulated for maximum resistance to extrusion, abrasion, particle embedment and tear. For low pressure or applications where excessive heat is a problem, the Nitrile (308 compound) is normally recommended. As a valve and its associated seat wear, they become a mated component. The valve and seat wear together to maintain a seal and prevent insert extrusion. If a valve is rotated or removed for inspection and re-installed, the valve and seat are no longer mated and must operate a length of time before they are mated again. During this time period the insert may extrude and the metal components may wear at an accelerated rate. If, when a valve and seat are installed, the end user uses apaintstick to put a mark through the valve and seat for orientation purposes, the valve can be inspected and re-installed in the same location. This will reduce insert extrusion and metal wear while still permitting periodic inspection. If the pressures are low enough to permit insert changes, the valve should still be re-installed back into its original seat and orientation to achieve maximum life. Installing a new valve in a used seat is never recommended. Installing a used valve from another seat is also not recommended. When installing a new valve and seat, a new spring should always be installed. The spring loses its spring rate (stiffness) over a specified time and number of actuations. A 50-lb/in spring can be reduced to a 5-lb/in spring over time. A lightweight spring can cause valve hammering and can damage both the valve and seat metal components thereby reducing life substantially. As a pump valve pot deck wears, the actual metal-to-metal seal area between the valve pot and seat is reduced. This contact area on a new valve pot and new seat should be a continuous band and, at a minimum, 80% the full height of the seat contact. As the valve pot wears, this contact band will still be continuous around the seat but the thickness of the band will gradually be reduced. At the point before failure, the continuous contact band could be ½ ″ or less. Once the band fails to be continuous, a washout between the seat and valve pot will occur. Once a seat is removed from the pot, this contact band can be visually inspected and preventative measures can be taken to eliminate or greatly reduce the possibility of valve pot washout.
The most common types of valve failure involve extrusion, abrasion, corrosion, chemical attack or heat. By a visual inspection of the failed valve and seat, most modes of failure can be easily identified. Inspected parts may show evidence of two modes of failure but one of those is usually the cause of failure, and the other the effect of the failure. EXTRUSION: Extrusion is the most common type of valve failure. If the metal part of the striking bevel of the valve does not contact the seat, a gap will be present. In operation, the insert material will flow into this gap. The amount of material that flows into the gap will depend on the gap size, the operating pressure and temperature. For a given gap size, the higher the operating pressure, the more of the insert material will flow into the gap. Once the material is into the gap, a portion of it can be pinched or severed off. This action, over time, results in a missing section of the insert at the insert/valve body interface. This results in a torn appearance. This tearing action of the insert can continue until a large enough section is lost to cause ultimate valve failure. The gap can be caused by solids in the system, misaligned or worn upper valve guide or installing a new valve into a worn seat. A gap can also be caused by re-orienting the existing valve in the same seat (rotating the valve). ABRASION: Simple abrasion is different than abrasion from corrosion. Simple abrasion is directly attributed to the fluid medium being pumped and its abrasive qualities. Sand, quartz, iron filings, etc. are all very abrasive materials. Even though the valve body and seat are heat treated to increase the hardness and the insert is highly resistant to abrasion, these components will abrade down. Fluid mediums with abrasive matter are continuously supplied to and through the valve and seat. This matter gets crushed into sharp pieces by the metal part of the valve and tries to embed itself into the insert material causing small tears. Over time the surface of the insert will wear down faster than the valve body and a loss of insert seal will take place. The valve will fail at this point. CORROSION : On a microscopic level, clean metal rusts instantly. As a valve actuates under pressure in certain fluid mediums, the insert wipes the adjacent seat area to clean metal. On a microscopic level, rust develops in this area immediately. After the next valve actuation, the insert wipes this rust off and the area is clean metal again. Over many actuations, small microscopic pits begin to form due to this rusting/wiping action. After time, these microscopic pits start to merge together and after still more time they grow to the visual stage. At this stage, this corrosion pitting with very sharp edges begins to abrade the insert. As the pitting continues and the pits grow larger, the more abrasive they are to the insert. Over time, the insert will be abraded to the point that there is no interference between the insert and the seat. At that point, the valve will fail. The time frame before failure depends on how corrosive the fluid medium is, how fast the pump strokes and the operating pressure. Rust protects metal from further rusting because it keeps some of the air from reaching the base metal. Since the other areas of the valve and seat do not get this wiping action, no corrosion pitting may be evident in these areas, only on the seat area adjacent to the insert. For conditions such as these, there are seats designed to resist this corrosion pitting. Some are flash chrome plated, some chrome plated and some electroless nickel plated. There are different plating materials for different seat designs. CHEMICAL ATTACK : Some chemicals and chemical compounds can inhibit the insert material. They can cause a reduction in mechanical properties, swelling of the insert or a breakdown of the insert material. Normally, if an insert has been inhibited by chemistry, the insert will soften. If the insert has softened, it may also have a solvent or hydrocarbon smell to it if inspected immediately out of the pump. Once out of the pump, the chemical that attacked the insert may start to evaporate so it is important to check it as soon as possible after removal. An insert inhibited by chemicals is not normally detected by visual means. HEAT : As the operating temperature increases, the physical properties of elastomers decrease. Normally, since the valve actuation produces very little frictional heat, the insert selection can be based on the maximum fluid temperature expected.
The Roughneck Drilling valve is a full open valve designed for maximum flow characteristics. It has a one-piece unitized case hardened alloy steel body with a snap on insert. The Roughneck Drilling valve with the standard polyurethane insert has a maximum temperature rating of 180º F (82º C), maximum pressure rating of 7,500 psi and is designed for a solids content from low to high. The limited metal-to-
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