Several Recommendations for the Storage and Maintenance of Idle Valves-NANJING YUENG SHING VALVE CO.,LTD - Control Valves and Manual Valves Made of Stainless Steel

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Several Recommendations for the Storage and Maintenance of Idle Valves

Release Date:

2020-12-11

1. Why should hard-sealed shut-off valves be preferred whenever possible? Shut-off valves are required to have the lowest possible leakage; soft-sealed valves offer the lowest leakage and thus excellent shut-off performance, but they are not wear-resistant and have poor reliability. From the dual perspective of minimal leakage and reliable sealing, soft-sealed shut-off valves are inferior to hard-sealed ones. For example, the full-function ultra-light regulating valve features a seal protected by a wear-resistant alloy overlay, delivering high reliability and a leakage rate as low as 10⁻⁷, which already meets the requirements for shut-off valves. 2. Why can’t double-sealed valves be used as shut-off valves? The advantage of a double-seat valve’s spool is its force-balanced design, which allows for a large pressure differential; however, its major drawback is that the two sealing surfaces cannot maintain simultaneous, tight contact, leading to significant leakage. If such a valve is artificially and forcibly employed in shut-off service, the performance will clearly be poor—even after numerous improvements, such as the double-seal sleeve valve, it remains unsuitable. 3. Why is the double-seat valve prone to oscillation at small openings? For single-seat valves, stability is good when the fluid flow is from open to closed; conversely, stability is poor when the flow is from closed to open. In a double-seat valve, the lower seat operates in the closed-to-open flow direction, while the upper seat operates in the open-to-closed flow direction. Consequently, at small openings, the closed-to-open seat is likely to induce valve vibration—this is precisely why double-seat valves are not suitable for operation at small openings. 4. Why do straight-stroke regulating valves have poor anti-blocking performance, whereas angle-stroke valves perform better? In straight-stroke valves, the valve plug throttles vertically, while the fluid flows horizontally in and out, inevitably causing sharp turns and bends within the valve chamber and resulting in a highly complex flow path (resembling an inverted “S” shape). This creates numerous dead zones where sediment can accumulate over time, eventually leading to blockage. In contrast, angle-stroke valves throttle horizontally: the fluid enters and exits horizontally, easily carrying away impurities, and the flow path is simple with minimal space for sediment accumulation, hence their superior anti-blocking performance. 5. Why are the stems of straight-stroke regulating valves relatively thin? Straight-stroke regulating valves operate on a simple mechanical principle: sliding friction is high, whereas rolling friction is low. In a straight-stroke valve, the stem moves up and down; even slight tightening of the packing can cause it to grip the stem tightly, resulting in substantial hysteresis. To mitigate this, the stem is designed to be very slender, and low-friction PTFE packing is often used to reduce hysteresis. However, this approach has drawbacks: a thin stem is more prone to bending, and the packing has a shorter service life. The best solution is to use rotary-stroke valve stems—that is, angle-stroke regulating valves—whose stems are 2–3 times thicker than those of straight-stroke valves and employ long-life graphite packing. Such valves offer superior stem rigidity and longer packing life, while also exhibiting lower friction torque and reduced hysteresis. 6. Why do angle-stroke valves have a larger shut-off pressure differential? Angle-stroke valves can handle a larger shut-off pressure differential because the resultant force generated by the fluid acting on the valve plug or disc exerts only a small moment on the rotating shaft, allowing them to withstand higher pressure differentials. 7. Why hasn’t the sleeve valve lived up to expectations as a replacement for single- and double-seat valves? Introduced in the 1960s, the sleeve valve saw widespread use both domestically and internationally in the 1970s, and by the 1980s it had become the dominant type in newly commissioned petrochemical plants. At the time, many believed that the sleeve valve could replace single- and double-seat valves, becoming the second-generation product. However, today this is no longer the case: single-seat valves, double-seat valves, and sleeve valves are all used equally. The reason is that, although the sleeve valve improves throttling characteristics, stability, and ease of maintenance compared with single-seat valves, its weight, anti-blocking performance, and leakage levels remain comparable to those of single- and double-seat valves. How, then, could it possibly replace them? Consequently, these valve types continue to be used side by side. 8. Why do rubber-lined butterfly valves and fluoropolymer-lined diaphragm valves have a short service life when used with desalinated water? Desalinated water contains low concentrations of acids or bases, which are highly corrosive to rubber. Corrosion manifests as swelling, aging, and reduced strength, leading to poor performance of rubber-lined butterfly valves and diaphragm valves. Essentially, this is due to the rubber’s poor resistance to corrosion. Although fluoropolymer-lined diaphragm valves were later developed to improve corrosion resistance, the fluoropolymer diaphragms themselves are vulnerable to repeated folding and tearing, resulting in mechanical damage and a shortened service life. The best solution today is to use ball valves specifically designed for water treatment, which can last 5–8 years. 9. Why is the use of piston actuators in pneumatic valves increasing? For pneumatic valves, piston actuators can fully utilize the air supply pressure, allowing for a more compact actuator design with greater thrust compared with diaphragm actuators. Additionally, the O-rings in piston actuators are more reliable than those in diaphragm actuators, making their adoption increasingly common. 10. Why is selection more important than calculation? Compared with calculation, selection is far more important and far more complex. Calculation involves only a simple formula-based computation; the key issue is not the precision of the formula itself, but rather the accuracy of the process parameters provided. Selection, on the other hand, encompasses many factors, and even a minor oversight can lead to improper selection, resulting in wasted human, material, and financial resources, suboptimal performance, and various operational problems, such as reduced reliability, shortened service life, and compromised operating quality.

　　1. Why should shut-off valves preferably be equipped with hard-seal designs?

　　For shutoff valves, the lower the leakage, the better; soft-seal valves offer the lowest leakage and thus excellent shutoff performance, but they are less wear-resistant and have poorer reliability. From the dual perspective of low leakage and reliable sealing, soft-seal shutoff is therefore inferior to hard-seal shutoff. For example, the all-function ultra-light regulating valve features a seal backed by a wear-resistant alloy overlay, delivering high reliability and a leakage rate as low as 10⁻⁷—a level that fully meets the requirements for shutoff valves.

　　2. Why can’t a double-sealed valve be used as a shut-off valve?

　　The advantage of a double-seat valve plug is its force-balanced design, which permits a large pressure differential; however, its major drawback is that the two sealing surfaces cannot maintain simultaneous, reliable contact, leading to significant leakage. If such a valve is artificially and forcibly employed for shutoff service, the performance will clearly be poor; even with numerous modifications—such as the use of a double-seal sleeve valve—it remains an undesirable choice.

　　3. Why is the double-seat valve prone to oscillation when operating at small openings?

　　For single-seat valves, stability is good when the fluid flow is of the “flow-open” type and poor when the fluid flow is of the “flow-closed” type. In a double-seat valve, there are two valve cores: the lower core operates in the flow-closed mode, while the upper core operates in the flow-open mode. Consequently, at small openings, the flow-closed core is prone to inducing valve vibration, which is why double-seat valves are not suitable for operation at small openings.

　　4. Why do straight-stroke control valves have poor anti-blocking performance, while angular-stroke valves have good anti-blocking performance?

　　In straight-stroke valves, the valve plug throttles in a vertical direction while the process fluid flows horizontally in and out, inevitably causing the flow path within the valve chamber to turn and reverse—resulting in a highly complex flow pattern that resembles an inverted “S.” This creates numerous dead zones where stagnant deposits can accumulate, eventually leading to blockage. In contrast, angle-stroke valves throttle in a horizontal direction: the fluid enters and exits horizontally, which readily carries away impurities and contaminants. Moreover, the flow path is simple, leaving very little room for deposit accumulation; hence, angle-stroke valves exhibit excellent resistance to clogging.

　　5. Why is the stem of a straight-stroke control valve relatively thin?

　　Straight-stroke control valves operate on a simple mechanical principle: sliding friction is high, while rolling friction is low. In such valves, the valve stem moves vertically; if the packing is even slightly tightened, it will grip the stem very tightly, resulting in significant hysteresis. To mitigate this, the valve stem is designed to be extremely slender, and low-friction PTFE packing is often used to reduce hysteresis. However, this approach introduces two problems: a slender stem is prone to bending, and the packing has a shorter service life. The best solution is to employ a rotary-stroke valve stem—that is, a quarter-turn control valve. Such valves feature a stem that is 2 to 3 times thicker than that of straight-stroke valves, paired with long-life graphite packing. This configuration provides superior stem rigidity, extended packing life, and—paradoxically—lower friction torque and reduced hysteresis.

　　6. Why do quarter-turn valves have a relatively large shut-off pressure differential?

　　Valves with angular-stroke actuation can withstand a relatively high shut-off differential pressure because the resultant force exerted by the process fluid on the valve plug or disc generates only a small torque about the rotational axis, thereby enabling the valve to handle substantial pressure differentials.

　　7. Why has the sleeve valve, despite being intended to replace single- and double-seat valves, failed to deliver the expected results?

　　Sleeve valves, introduced in the 1960s, were widely used both domestically and internationally in the 1970s. By the 1980s, sleeve valves accounted for a significant share of petrochemical units imported from abroad. At the time, many believed that sleeve valves could replace single- and double-seat valves, thereby becoming the second-generation product. However, this has not proven to be the case; single-seat, double-seat, and sleeve valves are now all employed on an equal footing. The reason is that, while sleeve valves offer improved throttling characteristics, greater stability, and easier maintenance compared with single-seat valves, their performance in terms of weight, resistance to blockage, and leakage levels remains comparable to those of single- and double-seat valves. How, then, could they possibly replace these traditional valve types? Consequently, the three types must continue to be used side by side.

　　8. Why do rubber-lined butterfly valves and fluorine-lined diaphragm valves have a short service life when used with desalinated water?

　　Desalinated water typically contains low concentrations of acids or bases, which are highly corrosive to rubber. This corrosion manifests as swelling, aging, and reduced strength; consequently, diaphragm valves and butterfly valves lined with rubber perform poorly. The root cause is the poor corrosion resistance of rubber. Subsequently, rubber-lined diaphragm valves were upgraded to fluoropolymer-lined diaphragm valves, which offer superior corrosion resistance; however, the fluoropolymer diaphragm is susceptible to fatigue failure under repeated up-and-down folding, leading to mechanical damage and a shortened service life.

　　The best solution today is to use a ball valve specifically designed for water treatment, which can last 5 to 8 years.

　　9. Why is the use of piston actuators in pneumatic valves increasing?

　　For pneumatic valves, piston actuators can fully leverage the air supply pressure, resulting in a more compact actuator design with greater thrust compared with diaphragm-type actuators. Additionally, the O-rings used in piston actuators are more reliable than those in diaphragm actuators, which is why their adoption is steadily increasing.

　　10. Why is selection more important than calculation?

　　Compared with calculation, equipment selection is far more important and far more complex. This is because calculation is essentially a straightforward application of formulas; the key issue is not the precision of the formula itself, but rather the accuracy of the process parameters provided. In contrast, equipment selection involves numerous factors, and even a slight oversight can lead to an inappropriate selection. Such errors not only result in the wasteful expenditure of human, material, and financial resources, but also fail to deliver optimal performance, giving rise to a host of operational issues, including reliability, service life, and operational quality.

China’s First Mandatory National Standard for Valve Products Comes into Effect

Working Principle, Safe Operating Procedures, and Troubleshooting of Pressure Testing Pumps

Latest News

China’s First Mandatory National Standard for Valve Products Comes into Effect

GB 26640-2011, “Code for Minimum Wall Thickness Requirements of Valve Bodies,” a national new-product standard proposed by the China Machinery Industry Federation and approved and promulgated by the General Administration of Quality Supervision, Inspection and Quarantine and the Standardization Administration of China, has been officially implemented across the national valve industry since September this year. This is China’s first mandatory national standard specifically for valve products. According to reports, some enterprises have neglected product quality in the manufacturing of valves; in order to cut costs, they have even compromised on materials and workmanship, thereby creating certain safety hazards in production. The implementation of this first national standard for valve products will maximize the safety of both equipment and personnel. Article 14 of the Standardization Law of the People’s Republic of China stipulates that the manufacture, sale, and import of products that do not comply with mandatory national standards are prohibited.

2021-01-28

Several Recommendations for the Storage and Maintenance of Idle Valves

2020-12-11

Working Principle, Safe Operating Procedures, and Troubleshooting of Pressure Testing Pumps

Working Principle of Pressure Testing Pumps Pressure testing pumps are primarily used as pressurizing equipment for various pressure vessels and equipment—such as chemical containers, pump bodies, valves, and pipelines—during pressure testing. Consequently, their most distinctive feature is their ability to deliver very high discharge pressures; typical pressure testing pumps can reach several hundred atmospheres, while ultra-high-pressure models may exceed ten thousand atmospheres. However, their flow rates are generally quite low, often less than 1 m³/h. Nevertheless, the small output flow does not prolong the testing time, because pressure testing of a vessel does not require the pump to completely fill the container before the test can be considered complete. The usual procedure involves first filling the vessel with liquid, then connecting a fitting to the pump’s outlet. Leveraging the principle that liquids transmit force uniformly, once the pump reaches a certain pressure at its outlet, the same pressure is simultaneously applied inside the vessel, thereby achieving the desired test pressure. The working fluid for pressure testing pumps is typically water, though pure mineral oil may also be used. These pumps are generally available in two main types: manual and electric. Manual pressure testing pumps, due to their high discharge pressure, are usually single-acting reciprocating plunger pumps. They consist mainly of a pump body, plunger, hand crank, and drain valve. Electric pressure testing pumps have a basic structure largely similar to manual models. Their cylinder comprises four single-acting plungers. The transmission mechanism relies on an electric motor driving a worm gear reduction unit, which in turn uses an eccentric cam on the worm wheel shaft to drive the plungers in a reciprocating motion. Safety Operating Procedures for Pressure Testing Pumps 1. Conduct pressure tests strictly in accordance with the specified requirements; test pieces must be clean, tidy, and easy to inspect. 2. Prior to testing, inspect the electrical system and grounding conditions, calibrate the pressure gauge, verify that the pump is operating properly and adequately lubricated, and ensure that the maximum scale of the pressure gauge is at least 1.5 times the test pressure. 3. During pre-test preparations, arrange the positions of the inlet and outlet ports. When filling the vessel with water for testing, first open the vent hole and remove the pressure gauge to allow all air inside the vessel to escape. Once water begins to flow from both the vent hole and the pressure gauge connection, reinstall the gauge and close the vent hole. 4. Increase pressure slowly and never exceed the specified limit; after the test piece has reached the target pressure, striking or hammering is prohibited. If defects are discovered in the test piece or associated piping, reduce the pressure to zero before addressing them; working under pressure is strictly forbidden. 5. For negative-pressure or low-pressure test pieces and small vessels, it is permissible to raise the pressure in one step to the designated level and then hold it for inspection. Larger-volume test pieces, however, should be pressurized and inspected in stages. 6. Test pieces must be placed securely and stably, and the tested areas must pass inspection without any leakage. 7. After completing the pressure test, drain the water and relieve the pressure before removing bolts. In winter, be sure to drain all water immediately after testing to prevent freezing damage to equipment. 8. Tighten bolts evenly to avoid localized deformation that could lead to rupture. 9. Pressure testing pumps must be operated by designated personnel; each test requires at least two people, with a dedicated supervisor on duty until the water has been fully drained. 10. Mark any defects found during inspection and record them in the pressure test log. Common Faults in Pressure Testing Pumps Pressure Does Not Rise or Rises Slowly 1. Loose switch, deformed steel ball, or non-sealing inlet valve. 2. Clogged filter screen or water inlet pipe, or leaks at pipe connections. 3. Leakage at the plunger area. Solutions: 1. Tighten the switch and replace the (3) steel ball, (14) glass ball, or G9Crl3 steel ball. 2. Replace the medium and clear any blockages to eliminate leaks. 3. Replace the YX sealing ring (9). Short Holding Time 1. Minor leakage at the outlet valve. 2. Leaks at other component connections. Solutions: 1. Clean the valve core and replace the sealing ring. 2. Tighten connection bolts and replace seals.

2020-12-11

Analysis of the Causes of Sticking in ZZYP Gas Control Valves and Corresponding Improvements

1. Introduction Rizhao Iron & Steel Co., Ltd.’s Power Plant Gas Comprehensive Utilization Power Generation Workshop currently operates eight 50 MW blast furnace gas-fired generating units, with a total installed capacity of 400 MW. It is currently the largest blast furnace gas–based cogeneration plant among domestic metallurgical enterprises, supported by eight 220 t/h boilers whose fuel is the surplus blast furnace gas generated during ironmaking. 2. Causes Analysis Based on years of experience in operating these regulating valves and thorough research, we have identified the following primary causes of valve sticking: 2.1 Improper Installation Method Most valves are currently installed vertically, with the valve disc axis perpendicular to the horizontal plane. While this arrangement ensures that the actuator is located at the top of the gas pipeline, the rear bearing of the valve is positioned at the bottom, where moisture and impurities in the gas tend to settle or accumulate over time. This buildup gradually fills the clearance between the bearing and the shaft, leading to corrosion and eventual jamming of the valve shaft. 2.2 Unreasonable Design Structure Repeated disassembly and maintenance have revealed that the clearance between the valve stem bushing and the valve body is often filled with foreign matter such as sludge, water, and rust deposits. Moreover, the original design features an excessively long bushing, causing the front and rear bushings to bear the frictional forces generated by the reciprocating motion of the valve stem. Over time, dust in the gas and rust particles from the pipeline easily enter these clearances, increasing rotational resistance. The accumulated debris eventually fills the gaps, effectively welding the valve stem, bushing, and valve body together and severely restricting the valve’s ability to move freely. 2.3 Gas Corrosion Currently, all blast furnace gas pipelines in domestic steel plants suffer from severe corrosion. The most noticeable manifestation is frequent pitting and cracking of expansion joints, resulting in gas leaks along the pipeline. Corroded valves and pressure-reducing devices also fail to operate properly. The corrosive nature of blast furnace gas poses serious safety risks to both equipment operation and the integrity of the gas pipeline network. Our own gas pipelines likewise exhibit localized corrosion, including gas leakage through perforations and dripping condensate from expansion joint bellows. These conditions clearly have a significant impact on the valves. To analyze the extent of gas corrosion, we collected gas samples from two separate gas pipelines in the power generation workshop for laboratory analysis. Table 1: Composition Analysis of Blast Furnace Gas (%VOL) High-temperature components such as H2, CO, and H2O also exert considerable corrosive effects on steel. Given the high water content in the gas—particularly since the power generation system is typically located at the downstream end of the gas network—the pipeline often contains substantial amounts of condensate. Testing has shown that the pH of condensate in Rizhao Steel’s gas pipelines ranges from approximately 5 to 6, with an electrical conductivity of about 2762 μS/cm. In addition, the condensate contains high concentrations of iron ions, chloride ions, and sulfate ions. Some studies indicate that Cl⁻ and SO₄²⁻ can induce stress corrosion. In terms of corrosion morphology in gas pipelines and associated equipment, non-uniform corrosion predominates, specifically manifesting as: (1) under-deposit corrosion, also known as crevice corrosion; (2) pitting corrosion; (3) localized corrosion; (4) erosion-corrosion; and (5) stress corrosion. The presence of condensate inherently increases the corrosivity of the pipeline, with higher conductivity accelerating the corrosion rate. The combined effect of contamination and corrosive properties in the gas medium is a major contributing factor to valve sticking. 2.4 Improper Operation Since the current blast furnace gas regulating valves do not operate in a closed-loop automatic control mode, their opening degrees are manually set by operators via the DCS. When the load remains relatively stable for extended periods, the valve disc may stay fixed at a particular angle without regular movement, which can also lead to inflexible valve operation. 3. Improvement Measures 3.1 Installation Method The installation method should be changed from vertical to horizontal to prevent impurities, moisture, and contaminants in the gas from settling in the bushing clearance due to gravity. 3.2 Reducing Gas Acidity Given the significant harm caused by acidic gas to the entire gas pipeline system, large valves, expansion joints, and other components, this issue has drawn the attention of senior management. The company has adopted a neutralization strategy by injecting alkaline solution into the gas pipeline at the TRT inlet. Analysis of condensate samples from the power generation gas pipeline indicates a pH value of around 6. 3.3 Improving the Diseased Bushing Design The bushing dimensions should be reduced: the front bushing length should be shortened from 400 mm to 200 mm, and the rear bushing length from 800 mm to 200 mm. In terms of material, stainless steel, as specified in JB/T1759-2010, should be replaced with cast copper alloy, grade ZCuSn10Pb1. Even if minor scaling occurs inside the clearance, the significantly reduced bushing length will cut friction by one-half to three-quarters, making valve operation much smoother. We are also offering this improvement proposal free of charge to the supplier, requesting that future valve spare parts be custom-made according to our specifications. During maintenance inspections, it was also found that the packing gland on the upper part of the valve stem was overly tight, and in some cases, the packing gland screws broke due to excessive torque. When re-machining the packing gland, the clearance should be appropriately increased, and the gap should be thoroughly greased to prevent gas leakage. 3.4 Process Improvements The operating procedures should be revised to require boiler operators to conduct operational tests on all blast furnace gas regulating valves every shift and meticulously record the setpoint and feedback values in designated forms. This will prevent the valve disc from remaining fixed at a single opening degree for prolonged periods, thereby reducing the risk of scaling and seizing of the valve stem. 3.5 Maintenance Strategy Four spare regulating valves should be procured, and a rotating replacement maintenance approach should be implemented. Whenever there is an opportunity to shut down the boiler, the valve exhibiting the most severe sticking, as determined by the operators’ routine testing, should be replaced. The removed valve should then undergo disassembly, inspection, and refurbishment, followed by lubrication and maintenance before being returned to service, thus minimizing downtime. 3.6 Lubrication and Maintenance Monthly lubrication and maintenance should be performed on the packing glands and front and rear bearings of online-operating blast furnace gas regulating valves, with thorough equipment inspections conducted to promptly monitor operating conditions. Instrumentation and control personnel should ensure that the control components (valve positioners) are protected against rain and corrosion, regularly check air supply pressure, inspect all air connection points for blockages or leaks, and verify the quality of compressed air. In addition, the compressed air supply pressure should be appropriately increased to enhance the output force of the actuators. Instrumentation personnel should adjust the pressure regulator upstream of the positioner to maintain a stable pressure of around 0.5 MPa. Each time a major boiler overhaul is scheduled, the pipeline should be cleaned to remove sludge, debris, and other impurities, thereby reducing wear and corrosion. 4. Implementation Results By establishing revised operating procedures and ensuring that operators continuously monitor the status of the regulating valves, we have achieved comprehensive equipment management—a practical attempt at condition-based maintenance. Following these improvements, the frequency of maintenance has decreased, with the average maintenance interval extending from the original 2–3 months to 6–8 months. The workload for maintenance personnel has been significantly reduced, and crucially, the flexibility and reliability of the regulating valves have been ensured, providing robust equipment support for the safe and stable operation of the boilers. This solution can also be extended to other large valves on the gas pipeline network.

2020-12-11

Current National Standards Catalog (Valves)

2020-12-11

025-84168256

ausval@aliyun.com

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