While there are many reasons why centrifugal pumps fail, a high percentage can be attributed to bearing failure caused by lubrication issues. In fact, according to a leading bearing manufacturer, lubrication accounts for up to 80% of all bearing failures (top image). Key factors that induce tribological failures include contamination, insufficient lubricant, improper lubricant, and excessively long relubrication intervals, all of which are preventable. Pump life could be extended by 30-50% by focusing on these four factors.

1. Proper lubrication

Proper lubrication is more than selecting the right oil or grease for the application. Lubrication refers to how the lubricant is kept in a clean and healthy condition in the pump.

Users cannot simply fill a pump full of oil and expect reliability – they must constantly monitor lubricant health, oil level and contamination to avoid unnecessary breakdowns.

One way to do this is through oil analysis. However, for many smaller pumps, the size of the oil pan coupled with an inability to extract a representative oil sample often means that the oil in many pumps remains unmonitored. To overcome this limitation, it is recommended to implement daily or weekly visual inspections, performed by operators, lubrication technicians or mechanics. To be effective, the inspection must include visual clues to help determine the health, cleanliness, and overall oil level in the pump. Inspection checklists should be developed that ask simple questions with binary answers such as:

• Is the oil clean and clear?
• Is the oil level halfway up the sight glass?

Done correctly, visual inspections can detect 80% to 90% of all lubrication problems before they become catastrophic and should be mandatory whenever operator rounds are used.

Unfortunately, many process pumps are not set up for visual inspections and must be modified to include simple hardware to detect major lubrication issues. The top image illustrates some simple, inexpensive hardware additions that greatly improve the “inspectability” of a small centrifugal pump.

Once suitably modified for visual inspections, inspection routes and check sheets should be developed to verify the following:

Oil level

Proper bearing lubrication requires the oil level to be maintained halfway up the rolling element in the oil sump (Image 4). If it is too low, a lack of lubrication may occur. If it is too high and bubbling, an increase in temperature and aeration may occur. For smaller pumps this can be a challenge as some ball bearings can be as small as half an inch which means controlling the oil level to within ±1 inch. Most pumps are fitted with a level plug at the correct level or a flat faced bullseye. Flat-faced bullseyes work well when the pump is new and in good lighting conditions. However, over time, flat-faced bubbles can become stained or cloudy, making it difficult to check the oil level. Instead, pumps should be fitted with a 3D bullseye which can be viewed more easily and is less prone to staining. Under no circumstances should a constant level bottle oiler be used to check if the pump is properly filled. The feed tube from the lubricator to the pump can become clogged so that the cylinder lubricator can sometimes be full of oil while the pump is running empty.

2. Bottom sediments and water bowls

Contamination of process water and fluids is a constant problem in some industries. Whenever water enters the bearing housing, it emulsifies with the oil or settles to the bottom of the oil pan. In either case, water can adversely affect lubrication performance. A pump running on an emulsified oil-water mixture will see up to 50% to 75% reduction in bearing life.

A simple way to detect the presence of water is to install a Bottom Sediment and Water Bowl (BS&W). This simple device should be installed in the pump drain, ideally below the lowest point of the oil pan. Since water is heavier than oil, it will naturally settle at the lowest point of the bearing housing. By installing the BS&W bowl at the lowest point, water can often be seen before it contaminates the oil that lubricates the bearings (Image 3).

The inclusion of a BS&W bowl has been added to the latest version of the American Petroleum Institute (API) 610 centrifugal pump standard used by the refining, petrochemical and natural gas industries.

3. oil color

Each time the oil degrades, the color and clarity of the oil may change. Although a change in oil color is not always indicative of a serious problem, a sudden change, as shown in Image 5, should be reason enough for further oil analysis. BS&W Bowls and 3D Oil Glasses are two great ways to visually observe and record oil color.

4. Desiccant Breather Inspections

In a previous Pumps & Systems article (“The Impact of Water on Pump Bearing Life”, August 2021), the author discussed the importance of controlling space humidity inside the bearing housing using a desiccant breather. However, a desiccant breather is more than just a means of preventing water from entering the pump. It can also serve as another visual inspection point. Due to the way air flows through a desiccant breather, the color indicator, which changes from blue to pink when saturated with moisture, will change color from bottom to top or top to bottom, depending on the circumstances. A color change from top to bottom indicates that water is present inside the bearing housing, possibly due to seal failure (image 6).

Like most rotating assets, pump life is closely tied to the health and cleanliness of the lubricant. By adding a few simple visual inspections to operators’ daily rounds, early warning signs of impending lubrication failures can be detected before a functional failure occurs.

What are the important considerations when selecting a coupling between a pump and a motor?

A pumping system typically requires three valves: an inlet (suction) shutoff valve, an outlet (discharge) shutoff valve, and a check valve between the pump discharge nozzle and the inlet valve. discharge stop to prevent reverse flow and protect the pump from back pressure. Occasionally, a foot valve may be fitted to the inlet pipe to maintain pump prime or to protect against reverse rotation.

However, the potential drawbacks of foot valves such as impacts on net positive suction head available (NPSHa) and the risk of water hammer (an overpressure caused by a sudden change in pump flow) must be considered. account.

Rigid Couplings, as the name suggests, provide a rigid connection between two shafts, meaning the shafts are joined by close tolerances that allow no misalignment. This type of coupling must transmit torsional and axial loads and is capable of the highest torques and speeds. Rigid couplings are primarily used on vertical pumps where the thrust bearings are located in the motor, and when used in conjunction with the lower drive bearing, rigid couplings provide pump shaft support for mechanical seals.

Although there are many variations of flexible couplings, they are all intended to work by connecting two shafts, transmitting rotational power and compensating for some shaft misalignment. The secondary features of these couplings can vary, resulting in different benefits associated with each type. Some of these secondary characteristics include shock load damping, vibration damping, accessibility for maintenance, electrical isolation or conductivity, limited end-floating capabilities, fail-safe properties, and Moreover. Jaw, shell, sleeve, tire, grid, gear, and disc are all different types of flexible couplings used in pump systems.

Application considerations when selecting a coupling include:

• transmit the required torque at one or more given speeds
• suitable for pump and drive shaft
• provide shaft end separation to allow removal of mechanical seal, allow removal of pump bearings and allow lateral shifting of pump and drive shaft
• adapt to misalignment
• providing end flutter limitation
• maintain the required degree of unbalance at one or more given speeds
• torsional vibration damping
• prevent the dispersion of stray eddy currents
• resistant to corrosive environments
• prevent the occurrence of sparks

For additional coupling information, refer to “American National Standards Institute/Hydraulic Institute (ANSI/HI) 14.3 Rotodynamic Pumps for Design and Application” at www.pompes.org.

Read more HI Pump FAQs here.

The Jordan, Knauff & Company (JKC) Valve stock index is up 7.3% over the past 12 months, and the broader S&P 500 index is up 12.7%. The JKC pump stock index rose 8.5% for the same period.¹

The Institute for Supply Management’s Purchasing Managers’ Index (PMI) fell 1.5 percentage points to 57.1% in March, the lowest since September 2020 of 55.4%. New orders fell 7.9 percentage points to 53.8%, while new export orders fell 3.9 percentage points to 53.2%. The backlog index fell to 60% from 65% in February.

The production index fell by 4 percentage points to 54.5%, while the employment index increased by 3.4 percentage points to 56.3% . Survey respondents reported lower rates of resignations and early retirements compared to previous months and improved internal and vendor work positions. The price index recorded 87.1%, up 11.5 percentage points from February. Fifteen of the 18 manufacturing industries recorded growth, with five of the six largest industries posting moderate to strong growth.

The Labor Department said employers added 431,000 jobs in March, the 11th month of job gains above 400,000. Job gains were seen in restaurants, manufacturers and retailers. Additionally, more than 300,000 women joined the labor force. There are still fewer women in the labor force than before the pandemic, while male levels have fully recovered.

The jobless rate fell to 3.6% from 3.8% a month earlier. The average hourly wage increased by 5.6% compared to last year. However, on average, annual inflation of nearly 8% wipes out workers’ earnings. The economy has about 1.6 million fewer jobs than in February 2020. Jobs in leisure and hospitality remain below pre-pandemic levels while retail has fully recovered.

In response to Russia’s invasion of Ukraine, the US Department of Energy pledged to release 30 million barrels of crude oil from the US Strategic Petroleum Reserve (SPR) to help ensure a supply adequate in oil.

Other member countries of the International Energy Agency have collectively agreed to release an additional 30 million barrels of oil from their emergency reserves, bringing total releases to 60 million barrels. SPR stocks have been declining in recent years.

At the end of February, the SPR held 580 million barrels of crude oil. This release commitment is the first emergency levy since 2011.

On Wall Street, the Dow Jones Industrial Average, S&P 500 Index and NASDAQ Composite gained 2.3%, 3.6% and 3.4% respectively in March.

Negotiations between Russia and Ukraine, slowing commodity prices and expectations of an interest rate hike by the Federal Reserve Bank helped stocks rally. For the quarter, the Dow Jones, S&P 500 and NASDAQ fell 4.6%, 4.9% and 9.1% respectively. The market was worried about a possible recession and weak economic data.

Reference

1 – S&P Return figures provided by Capital IQ.

When selecting the right equipment for an application, the liquid ring vacuum pump can be considered archaic and inefficient. However, labeling this technology that way may be an oversimplification. This article is intended to help judge the reputation of the liquid ring vacuum pump by outlining its common ground and positives (and potential negatives) with technical advice.

There is a reason liquid ring pumps are chosen for critical infrastructure applications such as power generation and offshore oil and gas – when applied correctly, they are reliable. That said, it is important to first summarize the disadvantages of liquid ring vacuum pumps: they consume more energy than alternative technologies and consume too much water.

Energy consumption

In applications with little or no condensable vapor loads, liquid ring pumps consume more energy to accomplish the same compression than comparably sized alternative technology such as a dry screw, dry claw, or vacuum pump. rotating paddles. The excess is usually published between 20% and 25%, however, depending on vacuum levels, it can be higher than this.

In applications that have large amounts of condensable vapors, this efficiency gap can be bridged (if not overcome) due to the “condensation effect”. In such applications, liquid ring pumps act as a direct contact condenser, reducing the volumetric gas charge inside the pump and, therefore, increasing the overall intake volumetric capacity. The greater the difference between the temperature of the saturated gas at the inlet of the pump and the temperature of the sealing fluid, the greater the effect. The condensation effect occurs with little or no consequence on the absorbed power. Under the right circumstances, the energy gap can be bridged and an additional generator is not needed.

Water consumption

Liquid ring pumps require a fluid to create the seal between the inlet and discharge pressures, which is fundamental to their operation. In many applications, this fluid is water, which is why liquid ring pumps are commonly referred to as water ring pumps. After fulfilling its function as a seal under pressure, the sealing fluid is expelled to the discharge in combination with the process gas. The liquid and gas phases are quickly separated, and what is done with the fluid establishes the net thirst of the pumps.

There are three potential scenarios.

1. In some applications, this sealing fluid is sent to a floor drain or other treatment system. This is called a once-through configuration and often what users think makes the liquid ring vacuum pump unnecessary.

Applications using this mode of operation are typically those expecting a high particulate load from the application since once-through operation continuously flushes the pump of potential material buildup. Essentially, this design avoids an awkward situation.

2. In other installations, the sealing fluid may be recycled, passed through a heat exchanger to remove the heat of compression and condensation, and then returned to the pump to complete another cycle of its mission. Called “total or complete” recovery, applications implementing this method are generally cleaner in the sense that the process gases should not contain excessive particulates. Additionally, full recovery facilities are often ones where continuous removal of contaminated water or condensed solvents is not desirable.

There will be other trade-offs to consider, depending on the type/design of heat exchanger and the level of vacuum required. In simple terms, a water-cooled heat exchanger will increase the cooling water requirements of the facilities, while an air-cooled heat exchanger will increase the overall power consumption and need to consider the environment of the facility and maximum ambient conditions.

For operation at coarse vacuum levels or for liquid ring pumps with large seal fluid flow rates, a recirculation pump may be required to overcome pressure drops in the seal fluid piping from the separator discharge to the pump.

3. In a partial recovery configuration, some of the hotter discharge seal fluid is recycled and combined with a fresh fluid supply before entering the pump. This effectively minimizes the amount of fresh liquid needed. Pump manufacturers will often quote partial recovery modes that can save up to 50% in fluid usage. The actual amount of savings will depend on the level of vacuum required, the fresh water temperature and the amount of heat added to seal liquid flow.

The sealing fluid setup can seem like an unlimited game of bets and strikes, or worse, a shell game of “hiding the utility requirement”. The good news is that the characteristics of the application (particle entrainment, presence of solvents, degree of condensable vapors) will often make one method more practical than others. Corporate energy and water initiatives can then be addressed by intelligently implementing the design and control scheme.

If there are liquid rings in an installation, users should check how they are configured. If installed in a once-through configuration, some minor piping can save money. Energy and water consumption are the two most cited shortcomings of liquid ring vacuum technology. Hopefully the above helps explain the circumstances under which these shortcomings might be mitigated.

Additional Benefits

Other benefits of liquid rings include:

Solvent recovery

In some chemical and pharmaceutical applications, it is desired to recover process gases (solvents) to sell them as a by-product or reuse them in the application. The use of a liquid ring pump with the solvent as the sealing fluid can be a solution to achieve this (see the condensation effect above) while maintaining a small footprint.

Temperature rise

When pumping gases with relatively low auto-ignition temperatures, it is desirable to maintain low temperatures. After all, fires are not good for productivity. In a liquid ring pump, the heat of compression and condensation is absorbed by the sealing fluid. Since liquids have higher specific heat capacities than vapors, the temperature rise in a liquid ring pump is much lower than in other dry-running technologies.

Constructive flexibility

Mechanically speaking, liquid ring pumps are much less complex than other technologies (especially dry-running alternatives). The shaft-mounted impeller is enclosed in the cylindrical body, which is capped by orifice plates and end housings, with tie rods holding it together. Tolerances between impellers, casing and end plates are wider than those found in dry-running claw or screw pumps, which require tight tolerances to create the seal between inlet pressures and of repression.

These wider tolerances, in addition to the lower temperature rise (and therefore less thermal expansion), make liquid rings more suitable for construction in varieties of metals. Additionally, liquid rings have seemingly endless design options for rotational speeds, bearing locations/lubrication, and seal types. Whether the application involves air or potentially toxic/corrosive vapors, there is a suitable liquid ring configuration.

Pumping capacities

Due to mechanical simplicity, liquid ring pumps are available in larger sizes for applications requiring high flow rates. For installations not requiring redundancy, this means that only one piece of equipment needs to be installed and maintained versus the multiple pumps that would otherwise be required.

Problems with rotor bearing systems are one of the major factors in pump failure. Today, pumps are often designed to operate at increased speeds and loads to improve their efficiency. These operating requirements require that particular attention be paid to the analysis of the rotor dynamics during the design phase. This includes simulations of bearings, seals and other pump components.

There are many types of pumps available for industrial applications. These pumps can be classified based on design, operating principles, special features, working fluid characteristics, configuration (centrifugal, axial, screw, helical, positive displacement) and much more. With each type of pump there are challenges in terms of modeling and analyzing the rotor-bearing system. On the other side of the coin, many methods and principles of rotor dynamics are similar for all rotating machines.

This article will focus on two basic pump types: horizontal and vertical, with no further design specification, to describe common approaches and differences with respect to rotor dynamics, bearings, and seal simulations.

Vertical vs. Horizontal Pumps: Design Differences

The main difference between vertical and horizontal pumps is the orientation and shape of the shaft. A horizontal pump has a shaft that is placed horizontally (Top Image), between the bearings or cantilevered. The vertical pump shaft is positioned vertically. The most common type of vertical pump is the vertical turbine pump (VTP) — Image 2. Vertical pumps (like VTPs) usually have long spaghetti-shaped shafts that are connected to the motor (above or below) via the coupling and supported by a thrust bearing at the top or bottom. Another design feature of vertical pumps is the column casing which influences the dynamic characteristics of the pump. These design specifications make a difference in how to approach rotor dynamics modeling and vertical pump analysis.

What makes rotor dynamics different from the vertical pump?

Flexibility

Vertical pumps have long shafts which provide more flexibility. These flexible shafts have closely spaced modes and a dense range of frequencies. In this case, resonant vibrations with high amplitudes may occur, especially if the pumps operate in a wide range of rotational speeds.

The casing structure of vertical pumps (pipe) is also flexible. With this in mind, the flexibility of the pipe casing, as well as the cup assembly, must be considered when calculating the stiffness characteristics of the intermediate radial shaft supports. In addition, the casing structure of a vertical pump can experience strong vibrations due to its flexibility, so the frequencies of the pipe must also be analyzed.

Axial forces

Vertical cantilever pumps supported by a thrust bearing at the top of the machine are loaded with axial pulling force resulting from gravity loads. Conversely, if the stopper is placed at the bottom of the machine, a compression force acts along the shaft. The pushing force of the paddle wheels further contributes to the tension and stiffening of the shaft. All of these forces change the rotor’s bending stiffness, natural frequencies, and critical speeds. It is therefore important to take these factors into account through a dynamic analysis of the rotor before a machine is put into service.

Bearings and seals

The bearing is one of the most critical parts of any pump. Bearings support the shaft and reduce friction on moving pump parts by maintaining smooth rotor rotation. Bearings also provide stiffness and damping to the rotor bearing system. Bearings used for pumps can be classified as radial (support the shaft laterally) and axial (suitable for axial loads). The most common types of bearings used for pump applications are ball and roller bearings, hydrodynamic oil film plain bearings (regulators) and swivel pad bearings (axial thrust load bearing).

In the context of pumps, seals are no less important. Like bearings, pump seals are the source of stiffness, damping and additional “mass” coefficients for the rotor-bearing system, which change the dynamics of the whole system. The natural frequencies of a pump for systems with bearings and seals differ from systems on rigid supports.

The modeling of the bearing-seal system differs in vertical pumps compared to horizontal pumps. One difference is a potentially large number of radial bearings that support long shafts in vertical pumps. In many cases, a high number of stages (e.g. helical/spiral stages) in a pump increases the number of bearings and seals – the total number of bearings and seals can reach into the tens. Image 4 gives an idea of ​​the number of elements that will need to be modeled to obtain accurate rotor dynamic results. The combination of a long shaft, increased tolerances and misalignments with what is objectively a large number of radial bearings can result in a rapid and non-linear change in bearing stiffness in bearings where the shaft line approaches the supporting wall.

The second difference, and potentially even more important than the previous one, is that the radial bearings of vertical pumps are lightly loaded (no gravity force in the radial direction), which complicates the estimation of dynamic bearing coefficients. Unloaded cylindrical bearings are a cause of stability problems in vertical pumps. Thus, nonlinear analysis is essential for an accurate assessment of the rotor behavior of vertical pumps with long shafts and unloaded bearings.

Finally, in submersible pumps, which are mostly VTPs, the bearings are in a pressurized environment and lubricated by the process fluid, often with contaminations. In addition, the working fluid mixture can change composition and the operating conditions of a pump (speed of rotation) are often variable. Thus, these radial bearings undergo accelerated wear, and the prediction of their characteristics is complicated given the random characteristics of the applied conditions. A worst-case model approach can be used to predict dynamics and reliability to avoid critical failures.

What effects must be taken into account regardless of the type of pump?

There are areas where the analysis is similar. Some other effects that are important and must be taken into account in the analysis of the rotor dynamics of vertical and horizontal pumps are:

• static and dynamic radial loads occurring at the location of the impeller due to uneven distribution of the clearance between the impeller and the volute
• the inertias and hydraulic imbalance forces that must be introduced at the location of the wheel
• effective added mass at the wheels and along the shaft
• dry, wet and process fluid conditions, as well as “as new” and “worn” clearances considered during bearing and seal analyzes
• the Lomakin effect: a force created at wear rings and throttle rings in a centrifugal pump
• other similar general and technical effects for most rotating machinery and presented in American Petroleum Institute (API) 684 standards²

Although the approaches and methods for modeling and analyzing horizontal and vertical pumps are often similar, vertical pumps have their own set of features that make rotor dynamics analysis and bearing and seal simulations more complex. The main challenges encountered in vertical pumps relate to construction and operating specifications, including:

• long shafts
• a lot of steps
• its bearings and seals
• unloaded radial bearings
• axial forces due to gravity

Due to these design features, vertical turbine pumps are more prone to vibration issues and structural/life issues. This can cause headaches for the rotor dynamics analyst dealing with these types of pumps. Fortunately, today’s engineers have access to digital tools that can be used to solve these headaches. Using advanced simulation software, dynamic standards and technical publications (e.g. References 1 and 2 below), these effects can be modeled and analyzed to ensure safe and reliable operation.

References

1. API, 684, 2019. API Standard Paragraphs. Rotordynamic Tutorial: Critical Lateral Speeds, Imbalance Response, Stability, Train Torsion, and Rotor Balancing, American Petroleum Institute, Washington, DC, USA.
2. API, 610, 2010. Centrifugal Pumps for the Petroleum, Petrochemical, and Natural Gas Industries, American Petroleum Institute, Washington, DC, USA.
3. SoftInWay Rotor Dynamics and Bearings User Manual: softinway.com/software-applications/rotor-dynamics/

How do I determine which type of boiler feed pump to select?

Boiler feed pumps can range from serving relatively small commercial boilers to large power plants. Small boilers can use a variety of pump types for this purpose. However, large power plants will use multi-stage rotodynamic pumps between bearings.

For pressures up to approximately 1800 pounds per square inch (psi) (125 bar), typical boiler feed pump types include multi-stage horizontal ring section designs (Type BB4, Image 1) or axial split case designs (type BB3), although in some applications there may be a preference for a double case pump (type BB5, Image 2). For higher pressures, the types of boiler feed pumps used are generally BB4 or BB5 types, with the BB5 types meeting the highest requirements in terms of pressure, flow rate and power.

There are no fixed rules for selecting the pump type for a specific boiler feed application. Much depends on the combination of manufacturers’ experience with applications and product offerings, as well as users’ experience with maintainability and reliability. If the plant is cycled instead of base loaded, special consideration should be given to using a sufficiently robust and proven pump design.

Some users choose to pay particular attention to the main construction features of the pump:

• Both ring section type BB4 and double casing type BB5 pump types have radial seals, which are geometrically simpler than the axial pump seal BB3.
• The BB4 ring section and BB5 double casing pump geometries inherently lend themselves to higher pressure containment. The double sump pump type has the highest containment
• for pressures above 3600 psi (250 bar).
• The BB5 double casing pump has fewer seals than the BB4 annular section pump.
• Type BB3 split case axial pumps and BB5 double case pump allow the entire assembled rotor to be removed and balanced as a unit. These rotors may have opposed wheel arrangements which reduce the hydraulic thrust carried by the thrust bearing.

Boiler feed pumps used by electric power utilities are typically constructed with 400 series stainless steel internals. Types BB3 and BB4 use 400 series stainless steel housings when the temperature pumping exceeds 120 C (250 F). The outer casing of the Type BB5 pump can be cast or forged steel, designed using the American Society of Mechanical Engineers (ASME) Section VII as a guide for pressure limiting and bolting. When a forged carbon steel material is used for the outer barrel, the internal surfaces exposed to high flow velocity may be welded metal coated with stainless steel to improve erosion resistance.

For more information on boiler feed pumps, see “Power Plant Pumps: Guidelines for Application and Operation” at www.pompes.org.

Read more HI Pump FAQs here.

What course of action should managers take when a clause in an industry standard no longer reflects the best available technologies or practices? The answer is: Go for the best technology available and, where appropriate, place relevant artwork, documentation, and thought processes in company records.

Although relatively rare, there are instances where technical clauses are outdated and best practices should prevail. The sealing of fire water pumps is one example, but other examples exist. This article discusses an incident in 2015 when a major overseas oil refinery suffered heavy losses due to a fire water pump shutting down on the day of a major fire.

In the early to mid-1950s, some knowledgeable multinational corporations with refineries and chemical plants around the world developed industry-standard supplements. These companies then overlaid and appended their “best practice addenda” applicable to nearly every industry standard they invoked or referenced when purchasing equipment. At least one company realized that among the items and details that needed to be changed were then-existing stipulations relating to fire water pumps. Although these stipulations were well-intentioned when first published, they were obsolete in 1965. One of the old clauses of the industry standard required braided packing in fire water pump glands. However, by the mid-1960s, companies with best practice addenda fitted these pumps with mechanical seals because the braided packing was at risk of more frequent breakdowns and unplanned failures.

There is a series of papers on the topic of fire water pump sealing upgrades, including articles stating that modern mechanical seals required less maintenance labor, leaked lesser controls and reduced frictional power losses by 50% compared to braided packing. All in all, modern mechanical seals are more reliable than seals in fire water service. By about 1965, single spring mechanical seals had become the best available technology for fire water pumps. In some cases, these mechanical seals had to be reinforced with a floating throttle ring and baffle. Since reliability professionals must advocate for “design” maintenance, they are also encouraged to inquire about the feasibility and desirability of safely installing a labyrinth-type advanced rotary bearing housing guard seal. Such protective seals should replace the deflectors used decades ago. In addition, these protective seals must incorporate axially or diagonally movable O-rings. Radial displacement O-rings near sharp-edged components have been prohibited by knowledgeable users.

Three layers of defense

If a facility still uses trim, maintenance and reliability managers would do well to reconsider. A leaky packing compromises the pump bearings. Because good managers strive to inculcate the habit of learning from others’ mistakes and demanding fact-based solutions, they may insist that their staff follow up. In their quest to make informed decisions, officials could ask reliability groups to research what happened at the aforementioned refinery in 2015. Asking to be informed of the total economic losses of the major refinery that suffered the calamity would be a good start. The main fire water pump at this refinery was out of service because a packing leak had compromised its bearings. On the day when water was desperately needed to fight a major fire, the pump was not available. It is a sobering fact that upgrades implemented elsewhere 50 years earlier had not been continued by overseas installation until mid-2015.

Interestingly, the thinking that led many leading oil refineries to switch to single spring mechanical seals instead of braided packing in fire water pumps as early as 1965. In the 1960s, accurate statistics were kept (for insurance purposes) by a major multinational oil company. well known to the author. Fire water pump statistics have shown that leaking packings tend to damage bearings. Well-designed mechanical seals were selected by the reliability-focused multinational because these seals typically leaked much less than the packing. Mechanical seals were found to be less likely to allow water spray to enter an adjacent bearing housing. Flimsy, old-fashioned mechanical seal faces can break with abuse, but clever material combinations for seal faces have been available for some time. Today, properly designed, selected and installed seals are highly unlikely to fail unexpectedly. Additionally, floating throttle rings represent a “second line of defense” and advanced bearing protection seals clearly represent a “third line of defense” in fire water pumps.

Testing and operation

The use of packings in modern fire water pumps is not recommended. The observation that packaging no longer represents best practice is amplified by the frequent lack of training of maintenance personnel observed in some factories. Best practices include periodic testing of all backup equipment. A frequently asked question concerns the testing and alternative operation of emergency equipment. Operators ask if switching pumps ‘A’ and ‘B’ and running them for a month, or starting the standby pump once a month and then running them for four to six hours, is the choice. prefer. When people said decades ago that factories could get away with testing only twice a year, reliability professionals took the position that testing only twice a year would not be acceptable. and that a monthly test was necessary. Depending on lubricant choice and lubricant application method, changing “A” and “B” every two or three months is considered best practice. This keeps the bearings lubricated and prevents the seal faces from sticking.

The much publicized reliability-focused practice of implementing mechanical seals for fire water pumps had not been accepted by the foreign refinery that experienced the fire in 2015. After this event, the refinery investigated why its main fire water pump was unavailable at a critical time. The comments aren’t all there, but presumably they closed the case after establishing that “a 50-year-old specification clause was met and therefore the incident is no one’s fault. “. Nevertheless, the claim that the packaging is safer was refuted by the company which had collected worldwide statistics for insurance purposes. He determined that the consistent use of modern cartridge seals would be the first step in ensuring that future results will be more favorable to pump availability and asset protection.

Any industry standard should explain the intent of its clauses. If there are better ways than following an obsolete clause, follow the path of reason and use what is safest for the factory and the community. Of course, when informed users deviate from an old industry standard, they carefully and authoritatively document why they deliberately switched to less risky methods. Corporate attorneys for the author’s petrochemical company agreed that in the event of a dispute, statistically proven best practices would prevail over an occasional but demonstrably outdated clause found in older industry standards.

A corrosive liquid is a fluid that attacks and destroys materials with which it comes into contact. Metals, stone, glass, and even some types of plastics can be susceptible to corrosion by corrosive liquids or chemicals, which fall into six categories: strong acids, weak acids, strong bases, weak bases, desiccants and oxidizing agents. Some chemicals may belong to more than one category. For example, sulfuric acid is a strong acid, desiccant and oxidant. Corrosives can also belong to other hazard categories such as toxicity (toxic) or flammability.

While corrosive liquids can destroy materials like glass and metal, they are obviously dangerous to humans. The U.S. Occupational Safety and Health Administration (OSHA) recognizes the health risks posed by these substances, defining them as “a chemical that produces destruction of skin tissue, namely visible necrosis through the epidermis and in the dermis, in at least one of the three animals tested after an exposure of up to four hours.Corrosive reactions are characterized by ulcers, bleeding, bloody scabs and, after 14 days of observation , discoloration due to whitening of the skin, complete areas of alopecia and scarring.

When a pump is used to transfer hazardous liquids in oil and gas dehydration, such as flammable, combustible, toxic and corrosive chemicals, it is essential that several factors are considered. These considerations are key to choosing the right pump for the job.

Considerations

First, the characteristics of the fluid. What type of fluid will be pumped? What are the characteristics of this fluid? This information can be found in the Fluid Safety Data Sheet (SDS, formerly known as Material Safety Data Sheet or MSDS).

According to an OSHA summary of the SDS, “HCS 29 CFR 1910.1200(g) requires the manufacturer, distributor, or importer of chemicals to provide SDSs for each hazardous chemical to downstream users to communicate information on these dangers… such as the properties of each chemical product; physical, sanitary and environmental health risks; Protective measures; and safety precautions for handling, storage and transportation of the chemical. The fluid SDS provides critical data such as concentration, specific gravity, temperature resistance, viscosity, flammability (if applicable) and solids content specifics.

Application requirements

To ensure that the pump is properly sized, users should also consider the pump manufacturer’s load capacity curve. A pump curve (also called a pump selection curve, pump efficiency curve, or pump performance curve) provides the information needed to determine a pump’s ability to produce flow under the conditions that affect pump performance. the machine.

Reading pump curves accurately – or consulting a pump professional who can – ensures users get the right pump based on application variables such as: head (such as the energy required to evacuate water from a pump at an equivalent height expressed in feet or meters); flow rate (the volume of liquid to be moved in a given period of time, i.e. gallons per minute [gpm] or cubic meters per hour [m³/h]); rotations per minute (rpm); impeller size, depending on pump performance; Powerful; Efficiency; and the Net Positive Suction Head (NPSH).

The right pump for an application

The most commonly used equipment for transferring corrosive petroleum and gaseous fluids is the centrifugal pump. Centrifugal pumps are energy efficient, available in standard flooded suction or self-priming, and come in a wide range of sizes designed to pump from a few gpm to thousands of gpm.

When pumping corrosive liquids, centrifugal pumps offer another advantage: mechanical seals. These seals will prevent leaks where the internal rotating shaft protrudes from the stationary pump housing. This is similar to how an automobile’s water pump uses a mechanical seal to prevent coolant leaking from the pump. A mechanical seal uses carefully machined flat rings of a durable material, such as carbon ceramic or silicon carbide, where one rotates with the shaft and the other is stationary. The pumped fluid moves between the seal faces and forms a lubricating film. If the pump is run without liquid (dry running), the friction causes the sealing faces to heat up rapidly, leading to seal failure.

If a mechanical seal fails as a result of dry running, liquid will leak from the pump. If the pumped liquid is water, this may only be an inconvenience. With corrosive fluids, a leak can cause harm to humans, potentially causing significant damage to surrounding infrastructure and possibly creating an environment in which users are no longer in compliance with regulatory agencies, such as OSHA . Additionally, there are downtime and cost (or mean time between failure) considerations. [MTBF]) when a pump needs to be taken out of service and repaired.

Suitable building materials

It is important to choose the correct pump materials of construction. This is especially critical when moving corrosive liquids. Failure to do so will cause corrosion of components that encounter the corrosive fluid, such as seals and O-rings, which can impact both pump performance and service life.

According to corrosionpedia.com, corrosion is defined as “the deterioration and loss of a material and its critical properties due to chemical, electrochemical and other reactions of the exposed surface of the material with the surrounding environment. Corrosion of metals and of nonmetals occurs due to gradual environmental interaction at the surface of the material.

Now, corrosion by itself is usually not that big of a problem. Suitable materials of construction, such as cast iron, bronze, manganese bronze, nickel-aluminum bronze, cast steel, and stainless steel, are readily available and capable of handling most corrosive fluids safely and efficient. It is important to understand the different types of corrosion, as well as the factors that contribute to the rate of corrosion, to select the appropriate materials.

It can be difficult to choose a material that can resist corrosion and additional factors, such as erosion and cavitation. A general rule of thumb in selecting suitable materials of construction is to first select materials that will resist corrosion, then select one that provides the most appropriate resistance to abrasion and/or cavitation. Here are some examples of corrosion users may encounter when using a centrifugal pump to move corrosive fluids.

Abrasion-Corrosion

Abrasion, or abrasive wear, is the removal of metal caused by the mechanical action of cutting or abrading solids conveyed in a pumped liquid. When the corrosive liquid being pumped also contains abrasive solids (abrasion-corrosion), high-alloy materials such as stainless steel are often required to ensure pump performance and life. In centrifugal pumps, the impeller is particularly sensitive. Although the housing can be damaged by this, the biggest problem is usually the impeller, along with the wear rings.

Cavitation-Abrasion-Corrosion

Most commonly occurring with high suction energy pumps, cavitation is the removal of metal due to high, localized stresses produced on the metal surface by the implosion of cavitation vapor bubbles. In an abrasive and corrosive cavitation environment, the base material is eroded as the abrasive particles are accelerated towards the surface of the wheel by the implosive force of the cavitation bubbles, accelerating the corrosion process.

Consult a professional

Although this is not a complete guide to pump selection when transferring corrosive fluids, we hope it provides users with an overview of the challenges, as well as some of the critical factors to consider when choosing a pump. There’s a lot to consider, from the type of fluid being transported to selecting the proper pump materials of construction.

Users should begin by gathering information about the fluid to be pumped. Second, gather information about application requirements and environmental conditions. Then consult a pump professional who can advise you on choosing the right pump for the job taking into account all of the above factors.

There is nothing unusual about the pumps used for unloading railway tank cars. Unloading wagons loaded with liquid tar, on the other hand, is less common. Due to its high viscosity, the raw material is difficult to handle. To optimize the unloading process, an end user who needed to unload raw tar from railcars was looking for a pump that could meet the following criteria:

• complete emptying of residues without pressurizing the wagons
• meeting the highest security levels
• the unloading process carried out with a single pump for economic reasons

In practice, this meant that four wagons containing raw tar had to be emptied with a single pump. Typically, such requirements are difficult to implement. An important criterion was the safety of dry running, which is usually not ensured by standard pumps.

Standard pumps are vented through an empty discharge line when stopped. The level of the liquid decreases as the pumping process progresses, more and more gas being entrained. Gas bubbles form, reducing performance and causing erratic operation. If the gas content is too high while the pump is running, the flow may stop completely. This stops the conveying process and the pump must be purged, resulting in downtime. Today, unplanned downtime is usually flagged by diagnostics and early warning systems.

The solution

For a manufacturer of centrifugal pumps, this was one of many challenges. The engineering team and the pump manufacturer provided advice and recommendations (image 1), from pump design to commissioning and beyond. Dry-running pumps with and without fluid-matched self-regulating pumping and sealing systems were available, and in this solution the vertical pump was fitted with a magnetic coupling and liquid-lubricated plain bearings.

This design combined the properties of vertical, self-regulating pumps with those of the horizontal, dry-running, hermetically sealed pump. The pump runs permanently dry and operates continuously in the pumped liquid. Grease lubricated roller bearings are protected against product vapors by a gas barrier.

The shaft air gap sealing concept of this type of permanently dry-running pump consists of several components. This is achieved by rear vanes and the gas barrier, which prevent product vapors from entering the bearing unit. The eddy current-free magnetic coupling hermetically seals the pump from the environment. Due to the vertical orientation of the pump, the bearing and sealing unit operates completely without contact with the product, even in the event of a sealing gas failure. Roller bearings are typically in service for more than five years of continuous operation.

In addition to economic and technical benefits, the solution offered maximum safety in the event of leakage, ease of use and savings in construction costs. Intrinsically Safe Centrifugal Pumps—pumps that, based on specific design principles that prevent hazardous conditions in the event of a malfunction—automatically adjust to varying feed rates.

The principle is based on balancing the pressure between the pump impeller and the supply container: when a fluid flows into a container, the liquid level rises until the inlet and the outlet of the container are in equilibrium. These control features operate without additional mechanical or electrical devices. These pumps deliver according to the flow and automatically reduce the flow without any pressure reduction at the impeller.

As a result, the net positive suction head (NPSH) is close to zero. This type of pump also has a self-venting function, which makes it insensitive to gas bubbles. The pumps generally operate without cavitation, can be run dry safely, and operate reliably.

The low pulsation pump keeps the product and bearing area separate, making it suitable for almost any fluid. Application areas range from gas-laden, viscous, hot or boiling liquids to liquids containing solids. Typical fluids include toxic liquids with special shaft seal requirements: titanium tetrachloride, liquid tar, or liquid gas. The pump can withstand fluid temperatures up to 400 C (752 F) without coolant. Self-regulating transport behavior does not require a minimum flow. Cavitation problems do not occur; the pump has a required NPSH value (NPSHr) < 0.1 meter (m). Lifespans can exceed 15 years.

In addition, costly planning and construction measures such as the construction of pits are not necessary. This makes this type of pump, which is installed at ground level, easier to install, operate and monitor. All four cars are emptied from below and the supply lines to the cars must be open. On start-up, the pump descends to the level of the pipe gauge. The liquid flows from the tank cars under the effect of gravity. The pump is only stopped when the minimum level in the pipe gauge is reached and therefore all wagons have been emptied.

Definition of dry-running safety

Many pumps use the fluid to be pumped to sufficiently lubricate the plain bearings and cool the seal used. Dry-running safety is the ability of a pump to operate permanently without fluid. This is achieved by decoupling the bearing and sealing unit from the pumped liquid.