How to Select a Ball Valve for Seawater Injection | Duplex Grades, PREN, Galvanic Corrosion
For many raw, aerated or chlorinated seawater injection systems, start by evaluating a trunnion-mounted ball valve with UNS S32750 or S32760 wetted metal parts. Duplex 2205 may be suitable for cooler, treated and deoxygenated water, but only after checking temperature, dissolved oxygen, chlorine, shutdown time and valve crevices. PREN helps compare alloy chemistry; it does not prove that a complete valve will resist seawater. Select the valve as one assembly. Check the body, ball, stem, seats, springs, drain plugs, coatings and fasteners. The valve must also withstand the maximum closing differential pressure, release trapped cavity pressure, tolerate the expected particles and provide enough breakaway torque after a long period without movement. Define the Water Average ocean water contains about 35 parts per thousand, or 3.5%, dissolved salts.[1] Typical seawater also contains about 19,000 mg/L of chloride.[2] Open-ocean surface water is commonly around pH 8.1, while oxygenated surface water may contain dissolved oxygen near 8 mg/L, depending on temperature, salinity and biological activity.[3][4] These values explain why ordinary stainless steel may struggle in seawater, but they are not design limits. Use the actual water analysis from the project. ISO 21457 includes utility and injection systems in its material-selection scope and requires the relevant corrosion mechanisms and operating conditions to be reviewed.[5] Input Information required Why it matters Water type Raw, filtered, chlorinated or deoxygenated seawater Treatment changes oxygen, solids and chemical exposure. Chloride Normal and maximum concentration Higher chloride increases pitting and crevice-corrosion risk. Temperature Normal, design and shutdown maximum Localized corrosion resistance usually falls as temperature rises. Dissolved oxygen Normal value and treatment-failure value Aerated water is usually more severe than properly deoxygenated water. Chlorination Chemical, normal residual, peak dose and duration Oxidizing chemicals can increase localized corrosion. Solids Maximum size, hardness and concentration Sand and debris can cut seats or damage ball coatings. Pressure Normal, design, pump shut-in, surge and reverse pressure The largest load may occur during closing or a pump trip. Shutdown Maximum stagnant period and preservation method Water can remain behind the seats after the main line is drained. Design life Required service life and inspection interval Some offshore projects target 20–30 years, so difficult-to-replace valves need a larger margin. Use the most severe condition that can actually occur. Normal water may be cool and deoxygenated, while startup water is aerated and shutdown water becomes warm and stagnant. Do not replace these conditions with a yearly average. Check the Valve Location A seawater injection system does not have one uniform service condition. The valve location changes the main risks. Intake valves may see aerated water, marine growth, sand, shells and chlorine. Filtered-water valves see fewer large particles, but oxygen and chlorine may remain. Deoxygenated-water valves normally see lower oxygen, but must also survive treatment failure, commissioning and air entry during shutdown. Pump-discharge valves usually see treated water but face higher pressure, closing load and surge. State the real filter performance. A 10 μm filter, a 50 μm filter and a 100 μm filter do not create the same seat duty. Particle hardness also matters: a soft 50 μm deposit and a hard 50 μm mineral particle can affect the seat differently. Include the largest particle expected during filter bypass or failure. For high-pressure duties, review the service against a duplex or super duplex trunnion ball valve. The trunnion ball valve selection guide also explains how pressure class, material and end connection work together. Choose the Alloy Material Representative PREN range When it may be considered Main limit 316L About 23–26 Freshwater or controlled low-chloride water Usually has too little localized-corrosion margin for raw or chlorinated seawater valve crevices. Duplex 2205 About 33–36 Cooler, treated, deoxygenated and drainable systems Needs close review of oxygen upsets, chlorine, stagnant periods and seat-pocket crevices. UNS S32750 About 40–43 Raw, aerated, chlorinated or difficult-to-drain seawater Not automatically suitable for every temperature or oxidant level. UNS S32760 Usually above 40 Projects that specify this grade or have qualified service experience The result depends on whether the project uses PREN or a tungsten-containing PREW formula. Higher alloy Depends on grade Warm chlorinated water, severe crevices or previous super duplex failures Higher price does not remove the need for good valve design and manufacturing. “2205” is a common family name linked to UNS S31803 and UNS S32205. State the exact UNS number, ASTM grade and product form in the purchase order. Do not rely on the name “2205” alone. S32750 and S32760 are both super duplex grades, but their chemical limits and alloy additions differ. S32760 commonly includes copper and tungsten. Any substitution must include a review of chemistry, mechanical properties, welding, heat treatment and corrosion testing. For more detail on body and trim options, see the guide to ball valve material selection. Use PREN Carefully PREN means Pitting Resistance Equivalent Number. A common formula is: PREN = %Cr + 3.3 × %Mo + 16 × %N PREN compares the chromium, molybdenum and nitrogen content of stainless steels. It is useful for screening alloy chemistry, but duplex performance also depends on heat treatment, phase balance, surface condition and valve crevices.[6] Example material Cr Mo N Calculated PREN 316L example 17.0% 2.2% 0.05% About 25.1 2205 example 22.0% 3.2% 0.18% About 35.4 S32750 example 25.0% 4.0% 0.27% About 42.5 These are example calculations, not guaranteed values for every heat. Calculate PREN from the actual material certificate for each main wetted part. The body, ball and stem may come from three different heats and may therefore have three different calculated values. PREN does not show: Water temperature or chlorine dose Crevice size and stagnant-water exposure Heat-treatment quality Harmful intermetallic phases Surface roughness or iron contamination Galvanic contact with another metal Particle or coating damage A PREN of 42 does not mean that a valve is safe up to 42°C. PREN is not a temperature limit. Even a 10–20°C increase in water temperature can change localized-corrosion behavior, especially where warm water is trapped inside a seat pocket or body cavity. Some specifications use a PREW formula
How to Choose a Ball Valve for Wet CO2 Pipelines | Carbonic Acid Corrosion, Overlay, Trim Materials
Choose a wet CO₂ ball valve by checking water, impurities, pressure, temperature and operating conditions—not CO₂ percentage alone. Carbon steel may work when water exposure is limited and the expected corrosion loss is acceptable. Continuous water, chlorides, oxygen, acidic impurities, sand or long service without inspection may require CRA overlay, corrosion-resistant trim, hard-coated sealing surfaces and seals tested for rapid CO₂ decompression. Check the complete valve rather than only the pressure-containing body. The ball, stem, seat rings, springs, bearings, body cavity, drain holes and elastomer seals can fail before the main body wall becomes too thin. CARILO’s API 6D forged ball valve guide explains the main full-bore, reduced-bore and fire-safe construction options used in pipeline service. Start with the Water Dry CO₂ is much less corrosive to carbon steel than CO₂ mixed with liquid water. Once CO₂ dissolves in water, it changes the water chemistry and supports corrosion reactions at the steel surface.[1] A simplified reaction is: CO₂(aq) + H₂O ⇌ H₂CO₃ The real water phase is more complex. It may contain bicarbonate, carbonate, dissolved iron, chlorides, oxygen, H₂S, organic acids, treatment chemicals and solid particles. These substances can change the corrosion rate and the type of damage. A valve can be harder to protect than straight pipe because water may remain in: The body cavity Seat pockets Stem and trunnion bores Spring pockets Drain and vent passages Seal grooves The rear side of seat rings These areas may remain wet after the main pipeline has drained. A closed valve cavity may also receive little or no fresh corrosion inhibitor. Iron carbonate may form on carbon steel and slow the average corrosion rate. It is not a permanent protective coating. Flow, sand, low pH and valve movement can damage it. Tests on X65 steel have also found localized corrosion beneath developing and apparently complete iron-carbonate layers.[2] A low average corrosion rate therefore does not prove that a seat pocket, sealing surface or narrow drain passage is safe. Define the CO2 Service Wet CO₂ pipelines do not all carry the same fluid. The source of the CO₂ changes the impurities, water conditions and operating risks. Service Common conditions Valve areas at risk Oil and gas production Produced water, chlorides, H₂S, organic acids, sand and corrosion inhibitor Seat pockets, ball surface, springs, drains and bearings Wet CO₂ gas Shutdown condensation, low-point water and intermittent wetting Lower body cavity, seat pockets and stem bore CCS pipeline Water excursions, oxygen, NOx, SOx, rapid pressure reduction and phase changes All wetted surfaces, elastomers, vents and relief passages For CCS service, define both normal fluid composition and possible off-specification conditions. DNV-RP-F104 covers CO₂ properties, safety, materials, design, construction and operation as connected parts of a CO₂ pipeline system.[3] Water, oxygen and nitrogen or sulfur oxides can interact and create more severe corrosion than pure CO₂ and clean water alone.[4] A CCS specification should state: Normal impurity limits Maximum water content Possible off-specification composition Maximum off-specification duration Water-monitoring method Shutdown and restart requirements Collect the Design Data Use operating ranges rather than one normal pressure and temperature. Required data Why it matters Minimum and maximum pressure Body rating, seat load, phase behavior and decompression Full temperature range Corrosion, toughness, seat strength and actuator output CO₂ concentration Gas-phase partial pressure and fluid behavior Water content Dew point and condensation risk Free-water rate How long and how much of the valve remains wet Chloride concentration Water conductivity, pitting and crevice corrosion Water pH and alkalinity Carbon steel corrosion and iron-carbonate formation H₂S concentration and partial pressure Sour-service cracking risk Oxygen, NOx and SOx Oxidizing and mixed-acid corrosion Organic acids Carbon steel corrosion and deposit stability Sand concentration and particle size Ball coating, seats, bearings and drain blockage Flow rate and pressure drop Erosion, turbulence and local cooling Corrosion inhibitor Whether protected carbon steel is practical Blowdown rate Low temperature and rapid gas decompression Operating cycles Seat, coating, bearing and actuator life The data should cover normal operation, start-up, low flow, shutdown, blocked-in conditions, cleaning, water carryover and emergency depressurization. Calculate CO2 Partial Pressure For a simple gas mixture, approximate CO₂ partial pressure can be calculated by multiplying absolute pressure by the CO₂ mole fraction. Total pressure CO₂ content Approximate CO₂ partial pressure 50 bar absolute 10 mol% 5 bar 80 bar absolute 20 mol% 16 bar 100 bar absolute 20 mol% 20 bar 120 bar absolute 50 mol% 60 bar For example: 100 bar × 0.20 = 20 bar CO₂ partial pressure This calculation is useful for initial gas-phase screening. It does not show whether water is present, how much of the valve is wet or whether the water contains chlorides, oxygen or acids. Dense-phase CO₂ requires a suitable thermodynamic model. Fugacity, water solubility, phase changes and impurity distribution cannot be fully described by simple multiplication. Assess the Corrosion Risk Do not judge valve life from one average corrosion rate. The review should include: Uniform corrosion during normal operation Localized corrosion during shutdown Under-deposit corrosion beneath sand or scale Corrosion during inhibitor failure Attack at CRA-overlay edges Crevice corrosion behind seats and seals Erosion-corrosion caused by particles or high velocity The following table shows calculated uniform wall loss. It does not include pitting, crevice corrosion, erosion or abnormal operation. Average corrosion rate 10-year loss 20-year loss 30-year loss 0.05 mm/year 0.5 mm 1.0 mm 1.5 mm 0.10 mm/year 1.0 mm 2.0 mm 3.0 mm 0.20 mm/year 2.0 mm 4.0 mm 6.0 mm 0.50 mm/year 5.0 mm 10.0 mm 15.0 mm A rate of 0.10 mm/year appears small, but it produces 2.0 mm of uniform loss over 20 years. A local pit can grow faster than this average value and may damage a seat pocket before the main body wall reaches its minimum thickness. Assess corrosion over the full temperature range. The highest rate may occur at an intermediate temperature where reactions are active but the iron-carbonate layer is still thin or unstable. A straight-pipe corrosion result should not be copied directly to every valve surface. A valve has
How Long Should a Cryogenic Ball Valve Extension Bonnet Be? | Insulation Thickness, Packing Temperature, Clearance
A cryogenic ball valve extension bonnet has no fixed length that works for every installation. It must keep the stem packing above the finished insulation, within the approved temperature range of the complete stem-sealing system, and accessible for inspection and replacement. For early layout, a non-cold-box ball valve may have a centerline-to-stuffing-box height near 200–350 mm. A cold-box valve may require 400–800 mm or more. These are planning ranges, not standard minimum dimensions. The final height must be no less than the largest of three values: the project or standard minimum, the height required to clear the insulation, and the height required to keep the packing warm enough. The selected design must also pass checks for stem twist, actuator weight, installation angle and thermal movement. What Sets the Length? Nominal valve size is only one input. Two DN 50 valves can have different body diameters, pressure classes, stem sizes and packing locations. Installation Main Requirement Insulated cryogenic line Body radius, insulation thickness and maintenance space Valve inside a cold box Centerline-to-wall distance and outside access Inclined valve stem Liquid position inside the bonnet and approved stem angle Large actuator or gearbox Stem twist, bonnet bending load and support Valve exposed to cold vapor Packing, actuator and accessory temperatures Custom long extension Thermal evidence and mechanical strength CARILO supplies forged cryogenic ball valves for low-temperature applications. The exact bonnet dimension should still be confirmed from the project conditions and approved drawing. Compare Fluid Temperatures The fluid temperature affects the bonnet temperature gradient, but it does not directly give the required length. The figures below are rounded reference temperatures at or near normal boiling pressure. Cryogenic Fluid Approximate Temperature Selection Note LNG About −161°C to −162°C Actual temperature varies with LNG composition and pressure Liquid oxygen About −183°C Also requires oxygen-compatible materials and cleanliness Liquid argon About −186°C Close to the lower part of the ISO 28921 temperature range Liquid nitrogen About −196°C Near the lower limit of ISO 28921-1 Liquid hydrogen About −253°C Outside the −196°C scope of ISO 28921-1 U.S. Department of Energy LNG research uses temperatures near −161°C for cryogenic LNG conditions.[1] Normal boiling-point data for oxygen, argon, nitrogen and hydrogen are available from the NIST Chemistry WebBook and NIST reference tables.[2][3][4][5] Define the Dimension “Bonnet length” can describe several different dimensions: Body surface to packing gland Body surface to actuator mounting face Valve centerline to top of stuffing box Fabricated extension-tube length Overall valve height These values cannot be compared directly. A supplier quoting a 300 mm tube may place the packing lower than another supplier quoting a 300 mm centerline-to-stuffing-box height. For project comparison, a practical reference is the distance from the valve centerline to the top of the stuffing box. The stuffing box is the metal chamber that holds the packing rings. The packing gland presses the rings against the stem and chamber wall. The actuator mounting face is above the packing and should not be used as a substitute for the packing position. Ask the manufacturer to show these points on the drawing: Valve centerline Maximum body radius Bottom and top of the packing set Packing gland and gland bolts Top of the stuffing box Actuator mounting face Extension inside and outside diameters Drain, vent and seat-injection connections Overall height Large trunnion-mounted valves often have wider bodies, larger stems and more external fittings than floating valves. Their insulation envelope should come from the actual drawing. See the trunnion-mounted ball valve selection guide for related construction details. Check the Standards ISO 28921-1:2022 covers the design, dimensions, materials, fabrication and production testing of metallic isolation valves used from −50°C down to −196°C. It includes ball and plug valves, but it does not replace project-specific insulation and clearance checks.[6] ISO 28921-2:2015 is the current published standard for low-temperature type testing. It verifies a defined valve design under stated test conditions. It does not automatically qualify every bonnet length, stem diameter, packing system or installation angle.[7] ISO 28921-2 also states that an actuator is not evaluated unless it is an integral part of the valve. A valve test report does not automatically qualify a separately selected actuator, positioner or solenoid. A second edition of ISO 28921-2 is under development and is intended to replace the 2015 edition. Purchase documents should therefore state the exact published edition required by the project.[8] ANSI/MSS SP-134-2025 covers cryogenic valves and includes requirements for body and bonnet extensions.[9] BS 6364:1984 still appears in older catalogues, but BSI lists it as withdrawn from July 2021. It should not be presented as the current standard for a new project unless the contract specifically requires it.[10] ASME B16.34 covers pressure-temperature ratings, materials, dimensions, examination, testing and marking for applicable industrial valves. ASME lists B16.34-2025 as the current edition.[11] ASME B31.3 covers process piping in petroleum, chemical, hydrogen and cryogenic plants. It applies to the surrounding piping, supports, movement, fabrication, examination and testing rather than directly calculating the bonnet length.[12] A standard minimum does not prove that the actual valve: Clears the finished insulation Keeps the packing within its approved temperature range Fits through the cold-box wall Leaves enough tool space Supports the selected actuator Has acceptable stem twist Measure the Insulation The packing gland should normally remain outside the permanent cryogenic insulation. Use the complete finished insulation thickness, including: Main insulation material Vapor-retarder layers Outer vapor barrier Sealant and overlap areas Metal or polymer jacket Removable cover Fire-protection layer where required Installation tolerance Do not add an assumed 10 or 20 mm without checking the project insulation drawing. Different systems use different jackets, joints and removable covers. Measure from the valve body, not from the connected pipe. For example: Pipe outside radius: 30 mm Valve body radius: 85 mm Finished insulation thickness: 100 mm If the calculation starts from the pipe radius, the finished insulation boundary will be shown 55 mm too low. The gland may then be partly covered after installation. Use the highest body surface that must remain insulated. Include body bolts, drain valves,
Can Ball Valves Be Used in Vacuum Service? | Seat Sealing Direction, Outgassing, Leakage Testing
Yes, ball valves can be used in vacuum service, but a normal pressure rating does not prove that a valve will hold vacuum. The valve must seal in the installed pressure direction, limit air entry through the stem and body joints, use materials with an acceptable gas load, and pass separate seat and external leakage tests. Clean soft-seated ball valves are often suitable for rough and medium vacuum. High vacuum, repeated bakeout, frequent cycling, particles or contamination-sensitive processes may require a specially built vacuum valve. Selection should be based on absolute pressure, effective pumping speed, gas type, temperature, seat design and measured leak rate—not only on the words “vacuum rated” or “bubble-tight.” Vacuum Range Vacuum is measured as absolute pressure. A lower absolute pressure means a deeper vacuum. The ranges below are common engineering descriptions, although the exact boundaries may differ slightly between industries. Vacuum range Approximate absolute pressure Ball valve use Rough vacuum 1,000 to 1 mbar Many industrial ball valves can work after leakage and material checks Medium vacuum 1 to 10−3 mbar Clean, vacuum-tested soft-seated valves are often suitable High vacuum 10−3 to 10−7 mbar Low-gas-load materials, controlled cleaning and helium testing are normally required Ultra-high vacuum Below 10−7 mbar Ordinary industrial ball valves are rarely the first choice These ranges are not fixed valve limits. A clean, purpose-built valve may work at a lower pressure than expected. A contaminated valve with weak stem packing may cause problems even in rough vacuum. ISO 3529-1 provides the general vocabulary used in vacuum technology.[1] With one port near atmospheric pressure and the other near zero absolute pressure, the differential pressure is about 1.013 bar at standard atmospheric conditions. Most industrial valve bodies can withstand this load. The harder task is controlling very small gas flows through the seats, stem seals, body joints and non-metallic materials. Pressure Rating A Class 150, Class 600, PN16 or PN40 rating mainly describes the valve’s positive-pressure capability at a stated temperature. It does not prove that the valve can maintain a low vacuum pressure. A normal pressure rating does not confirm: Leakage across the closed ball Outside air entering around the stem Leakage through body gaskets Gas passing through elastomer seals Outgassing from seats, grease or cleaning residue Leakage after heating or repeated operation ISO 5208 covers pressure-boundary and closure-tightness testing for industrial metallic valves.[2] These tests remain useful, but a water or compressed-gas pressure test is not the same as a vacuum helium test. ASME B16.34 covers pressure-temperature ratings, materials, dimensions, testing and marking for several forms of industrial valves.[3] Vacuum testing should be added to these mechanical requirements, not used instead of them. Positive-pressure strength still matters. A vacuum line may see nitrogen purging, cleaning pressure, pump backpressure or an upstream process fault. Liquid trapped inside a closed valve cavity can also produce high pressure when heated. Carilo’s API 6D ball valve factory acceptance test guide explains common shell, seat and functional checks. API Specification 6D defines manufacturing and testing requirements for pipeline valves, but it is not a complete high-vacuum qualification standard.[4] Sealing Direction The direction of the pressure difference can change how tightly a ball valve seals. This is especially important in floating ball valves. When one port is at atmospheric pressure and the other is under vacuum, pressure pushes a floating ball toward the vacuum-side seat. That seat normally carries most of the pressure-assisted sealing load. The two seats may use the same material but still perform differently because of: Different initial compression Machining tolerances Relief grooves behind one seat A vent hole in the ball Different cavity passages Unequal seat support A valve may pass the required leakage limit in one direction but fail after the pressure direction is reversed. The test certificate must identify the vacuum port, higher-pressure port and test direction. Before installation, confirm: Whether the ball is floating or trunnion mounted Which port faces the vacuum chamber Which port normally sees the higher pressure Whether the seats are mechanically symmetrical Where the ball and cavity vents are located Which direction was used during factory testing Whether pressure can reverse during operation Do not select the vacuum direction only from an external flow arrow. Ask for a sectional drawing that shows the ball, seats and vent passages in the closed position. Low Pressure Difference A floating ball receives strong pressure-assisted sealing when one side is at atmospheric pressure and the other side is under vacuum. It receives much less help when both sides are already at low pressure. Pressure condition Approximate differential pressure Effect on floating ball Atmosphere versus 10−3 mbar About 1,013 mbar Strong pressure-assisted seat loading 10−2 versus 10−4 mbar 0.0099 mbar Very little pressure-assisted seat loading The two examples differ in pressure differential by roughly 100,000 times. This is why a valve that seals well between atmosphere and vacuum may perform differently when both ports are already evacuated. At low differential pressure, sealing depends more on: Initial seat preload Seat elasticity Ball roundness Ball surface finish Seat alignment Spring loading Correct actuator stops Pressure Force and Valve Size The force pushing a floating ball toward the lower-pressure seat increases with the projected area exposed to the pressure difference. The simplified relationship is: Force = pressure difference × projected area The following values use a differential pressure of 1 bar and a circular projected area. They are theoretical examples, not actual actuator-torque or seat-contact values. Projected diameter Projected area Force at 1 bar differential 50 mm About 1,963 mm² About 196 N 100 mm About 7,854 mm² About 785 N 150 mm About 17,671 mm² About 1,767 N Doubling the projected diameter increases the area and pressure force by about four times. Larger floating ball valves can therefore develop much higher seat loading, operating torque and polymer deformation than smaller valves. The actual load depends on the ball geometry, port size, seat diameter, body clearances and friction. These figures should be used to understand the scale of the force, not to size an
Ball Valves for Thermal Oil Systems | High Temperature, Fire Safety, Stem Sealing
A thermal-oil ball valve should be selected from the maximum continuous temperature, pressure at that temperature, shutoff differential pressure, oil condition and operating frequency. For clean oil within a verified soft-seat rating, a reinforced polymer seat may provide tight shutoff and low torque. At about 300°C or higher, a metal-seated valve should normally be checked first unless the manufacturer can prove that a complete polymer-seated valve is suitable for the stated temperature and pressure. A valve that passes a room-temperature water test can still leak, seize or require excessive torque after repeated heating and cooling. Before purchase, obtain the valve pressure-temperature chart, seat-leakage limit, hot torque data, cavity-relief arrangement and a list of all nonmetallic parts. Operating Data Start with the exact heat-transfer-fluid name. Mineral oil, synthetic aromatic fluid, silicone fluid and food-grade thermal oil can have different viscosity, thermal stability and fire properties. Record four temperatures: Normal operating temperature: the temperature during most operating hours. Maximum continuous temperature: the highest temperature expected for long periods. Maximum upset temperature: the highest short-term temperature during stopped flow or another fault. Minimum startup temperature: the lowest temperature at which the pump and valve may operate. Condition Example value Main effect on the valve Normal temperature 280°C Seat wear, packing life and normal torque Maximum continuous temperature 320°C Seat creep, gasket relaxation and material strength Upset temperature 330°C for 30 minutes Permanent seal damage or thermal seizure Minimum startup temperature 10°C High oil viscosity, pressure loss and actuator torque Packing-chamber temperature Measured or calculated Stem leakage and packing life Actuator mounting temperature Measured at the bracket Actuator seals, switches, solenoids and cables In this example, the valve may move from 10°C during startup to a 320°C design condition. That is a 310°C temperature change. The ball, seats, body, stem and packing do not all expand by the same amount, so a valve that turns freely when cold may become tight when hot. Cold oil can also be much more viscous than hot oil. Higher viscosity increases pipe resistance, pump discharge pressure and the force needed to move oil through the valve cavity. Use the viscosity curve for the actual fluid at 10°C, not only its value at 280°C. Do not use heater film temperature as the valve temperature. Film temperature is the temperature of the thin oil layer next to a heated surface. A valve normally sees the local bulk temperature, although a valve close to the heater may continue heating after circulation stops. The packing chamber may be cooler than the oil because the valve neck releases heat to the air. Covering the whole neck with insulation can raise the packing and actuator temperature. For heavily insulated valves, ask for the expected temperature at the gland and actuator bracket. Pressure at Temperature A pressure class is not a fixed pressure limit at every temperature. As the body material becomes hotter, its permitted pressure normally falls. ASME B16.34 covers pressure-temperature ratings, materials, dimensions, examination, testing and marking for many flanged, threaded and welding-end valves.[1] Do not specify only: DN100, Class 300, carbon-steel ball valve. State the full condition: Design pressure: 18 bar Design temperature: 320°C Maximum shutoff differential pressure: 12 bar Minimum startup temperature: 10°C The valve body pressure-temperature rating must cover 18 bar at 320°C. Saying that a body is simply “rated for 320°C” is incomplete because pressure and temperature must be checked together. The seat must also hold 12 bar differential pressure at 320°C. The metal body may remain structurally suitable after a polymer seat has already softened, crept or lost sealing force. Valve condition Upstream pressure Downstream pressure Seat differential pressure Valve open during circulation 15 bar 12 bar 3 bar Valve closed, downstream still pressurized 15 bar 5 bar 10 bar Valve closed, downstream depressurized 15 bar 0 bar 15 bar This example shows why normal running differential pressure cannot be used for seat selection. The seat may see only 3 bar while the valve is open but the full 15 bar after the downstream line is drained. Check all credible pressure conditions: Normal pump discharge pressure Maximum pump pressure Pump shutoff pressure Cold-start pressure Static head Expansion-tank or nitrogen pressure Maximum closed-valve differential pressure Pressure trapped inside the body cavity A room-temperature shell or seat test confirms the valve under the stated test conditions. It does not prove long-term hot performance. ISO 5208 defines pressure testing used to check the pressure boundary and closure tightness of metallic valves.[2] Valve Design A floating ball valve uses line pressure to move the ball slightly toward the downstream seat. The design is compact and common in smaller sizes, but seat load and operating torque increase with differential pressure. A forged soft-seated floating ball valve can suit clean thermal oil when temperature, pressure and cycling remain inside the verified seat rating. A trunnion-mounted valve supports the ball at the top and bottom. Spring-loaded seats move toward the ball. This design is often used for larger sizes, higher differential pressure and automated isolation because torque is usually easier to control. The forged trunnion-mounted ball valve provides an example of a supported ball with spring-loaded seat assemblies. Condition Floating ball Trunnion ball Typical application Small and medium isolation valves Medium and large automated valves Ball support Supported mainly by the seats Supported by upper and lower trunnions Pressure effect Pressure pushes the ball onto the downstream seat Pressure and springs move the seats toward the ball Torque at high differential pressure Can rise sharply Usually more predictable Cavity arrangements Usually simpler SPE, DPE and hybrid arrangements are common One-piece valves have fewer body joints but may be difficult to repair. Two-piece valves provide access to the ball and seats. Three-piece valves can allow the center section to be removed while the pipe ends remain installed. Every body joint needs a gasket and enough bolt load. Repeated heating and cooling can relax the gasket or bolts, causing a slow external leak. The quotation should identify the gasket material, bolting grade and tightening method. Bore
Ball Valves for Produced Water Service | Chlorides, Sand, Corrosion-Erosion, Coating Options
A produced-water ball valve should be selected from five facts: water chemistry, sand and scale, pressure and temperature, operating method, and required leakage rate. Corrosion-resistant alloys or weld overlay protect against chlorides, CO2 and H2S. Metal seats and carbide coatings improve resistance to sand, but they do not stop wear completely.The body, ball, seats, stem, springs, seals and coatings must all suit the same service. Selecting a valve only by pipe size, pressure class or chloride concentration can leave small internal parts unprotected. Data to Collect First The following values should appear in the valve data sheet. The units matter because terms such as “high chloride” or “some sand” are too vague for material selection. Parameter Unit or Data Format Why It Matters Total dissolved solids mg/L Shows overall water salinity Chloride mg/L Affects pitting and crevice-corrosion risk Dissolved oxygen µg/L or ppb Can increase carbon steel corrosion and change stainless steel behaviour CO2 and H2S Dissolved concentration or partial pressure Affects corrosion and sour-service material limits Sand concentration mg/L or mass percentage Affects seat and coating wear Particle size d50, d90 and maximum size in µm Shows whether particles can enter seat clearances or block closure Pressure and temperature bar or MPa; °C Controls pressure rating, material limits and actuator torque Differential pressure bar or MPa Controls local velocity and erosion during operation Operating torque N·m Provides a baseline for detecting sand, scale or internal damage Define the Service Produced-water conditions change with the valve location. State where the valve will be installed before selecting materials. After a separator: water is the main phase, but oil, dissolved gas, fine sand and scale may remain. After water treatment: solids may be lower, while oxygen, bacteria and treatment chemicals may become more important. Water injection: the valve may face high pressure, oxygen entry, mixed-water scale and long shutdowns. Water disposal: deposits may collect during low flow or stagnation. Drain and flushing lines: short periods of very high solids loading may occur. A valve upstream of the separator is exposed to oil, gas, water and slugs. It should be treated as multiphase wellstream service, not produced-water-only service. For main pipeline isolation, bore, seat arrangement, pressure class and testing may need to follow an API 6D forged ball valve design. Check the Water Use a recent water analysis from the actual valve location. Produced-water chemistry can change as water cut rises, injection water reaches the well, treatment chemicals change or separation performance falls. The analysis should include: Chloride and total dissolved solids pH and alkalinity Dissolved oxygen Dissolved CO2 and H2S Gas composition and total pressure Calcium, barium, strontium and sulfate Dissolved iron Oil and grease Suspended solids Corrosion inhibitor Scale inhibitor Biocide Methanol, glycol and other injected chemicals USGS data show that conventional oil and gas produced waters can range from about 5,000 mg/L to more than 350,000 mg/L total dissolved solids. Chloride, sodium and calcium are commonly the main ions.[1] The USGS National Produced Waters Geochemical Database contains records from roughly 18,000 oil, gas and brine wells, showing how widely water chemistry can vary between fields.[2] Check the Sample A laboratory report is useful only when the sample represents the pipeline conditions. CO2 and H2S may escape when pressure is reduced. Oxygen can enter the bottle during sampling. Sand results can change sharply between normal production, startup and separator upset. Record: Sampling point and date Line pressure and temperature Normal, startup or upset operation Whether the sample was depressurized Whether chemical injection was running How the sample was protected from air How quickly unstable components were tested For severe service, compare samples from normal production and credible upset conditions. One clean sample may miss the condition that causes valve failure. TDS and Chloride Total dissolved solids and chloride are not the same measurement. TDS is the approximate total amount of dissolved material. Chloride measures only chloride ions. Two water samples can have the same TDS but different chloride, calcium, sulfate and bicarbonate levels. Chloride affects stainless steel pitting and crevice-corrosion risk. Calcium and bicarbonate affect calcium carbonate scale. Barium, strontium and sulfate affect hard sulfate scale. Dissolved iron may indicate corrosion or iron-containing deposits. Do not use one chloride limit to choose between 316L, duplex, super duplex and nickel alloy. Temperature, oxygen, pH, H2S, deposits, weld quality and stagnant crevices also affect the result. Check the Solids “Sand present” is not enough information. Ask for: Normal and maximum sand concentration d50 and d90 particle size Maximum particle size Particle shape and mineral type Scale particle size Sand-slug duration Startup and flushing conditions d50 is the size below which 50% of the measured particles fall. d90 is the size below which 90% fall. These values show whether a low average result hides a smaller number of large particles. Practical Particle Band Main Concern Possible Valve Damage 10–50 µm Fine particles entering narrow clearances Sand buildup behind seats, higher friction and rising torque 50–250 µm Repeated abrasive impact Seat scratches, coating wear and loss of sealing contact 250 µm–1 mm Large particles reaching the sealing band Deep scratches, seat indentation or incomplete closure Above 1 mm Large sand, scale or debris Immediate blockage or mechanical damage during closing These particle bands are practical review groups, not fixed material-selection limits. Particle shape, velocity, concentration and pressure difference must also be considered. Four solids patterns need different checks: Continuous fine sand: particles can enter the narrow space behind the seat. Short sand slugs: a high concentration can cut the downstream seat in a short time. Large startup particles: one particle may prevent full closure. Detached scale: hard, sharp scale can damage the ball and seat like sand. Quartz is hard enough to scratch polymer seats and poorly supported coatings. Actual wear also depends on particle velocity, size, shape, concentration and impact angle. Check the Flow Provide: Normal and maximum flow rate Actual pipe inside diameter Normal and maximum velocity Gas volume fraction Maximum differential pressure Flow direction and possible reverse flow Operating frequency Time
How to Check Whether a Full-Bore Ball Valve Is Truly Piggable | Bore ID, Pipe Schedule, Transition Geometry
Short answer: A full-bore ball valve is truly piggable only when the exact pig can pass through the finished valve, seats, connections, and adjoining pipe. Check the smallest finished bore, pipe Schedule, internal steps, welds, gaskets, transition length, and actual ball position. The words “full bore” alone are not proof.API 6D covers the design, manufacture, materials, assembly, testing, marking, and documentation of pipeline valves. It does not confirm that one valve can pass every cleaning pig or in-line inspection tool.[1] API has also issued Addendum 3 for the 25th edition, so the purchase specification should state the applicable edition, addenda, and errata.[2] For a basic comparison of full-bore and reduced-bore designs, see this full-bore ball valve guide. Know the Basic Terms NPS and DN are nominal size names. They are not exact inside diameters. OD is the pipe outside diameter. ID is the inside diameter available to the pig. Pipe Schedule identifies a standard wall-thickness series. For the same NPS, a thicker wall normally gives a smaller ID. Full bore describes the valve-port design. It does not prove that the valve bore matches the actual pipe ID. Offset, also called hi-lo at a welded joint, means that the pipe and valve bores do not share the same centerline. Clock position describes where a feature sits around the bore. Twelve o’clock is the top, six o’clock is the bottom, and three and nine o’clock are the sides. Start With the Pig Identify the exact pig before checking the valve. A foam pig, cup pig, disc pig, gauging pig, geometry tool, and intelligent inspection tool can have very different limits. Ask the pig supplier for: Maximum rigid outside diameter Minimum permitted clear bore Maximum inward step Maximum joint offset Maximum restriction length Minimum bend radius Permitted speed range Required pressure difference Bidirectional capability Do not rely on a statement such as “the pig can pass a 10% restriction.” Ask what the percentage is based on: Tool outside diameter Nominal pipe ID Measured pipe ID Diameter reduction Cross-sectional area reduction Also ask how long the restriction may continue. A 5 mm-long seat edge does not affect a pig in the same way as a 500 mm-long reduced bore. API Standard 1163 covers the qualification, selection, reporting, verification, validation, and use of in-line inspection systems. It does not provide one universal valve-bore or step limit for every inspection tool.[3] Check three separate questions: Can it pass? The tool must not become stuck or damaged. Can it keep moving? The line must provide enough pressure difference to overcome friction and restrictions. Can it inspect correctly? Sensors, wheels, magnets, or ultrasonic probes must remain in a usable position. A tool can pass through a valve but still produce poor data if it moves too fast, loses wall contact, or becomes unstable inside the body cavity. Compare Pig and Bore Size Use the smallest opening in the complete installed path: Available Bore ≥ Pig Supplier’s Minimum Bore The smallest opening may be at the: Pipe Valve end Seat ring Seat retainer Ball port Weld root Flange gasket Internal lining Suppose the smallest finished valve opening is 197.6 mm and the pig requires 193.0 mm: Diametral Margin = 197.6 – 193.0 = 4.6 mm If the pig and bore are perfectly centered: Radial Margin = 4.6 ÷ 2 = 2.3 mm per side The 4.6 mm value is the total diameter difference. It does not mean there is 4.6 mm of space on each side. For rigid circular tool modules, the minimum clear circle controls passage. Flexible foam, cups, and discs may deform through a smaller or oval opening, but the rigid shaft, body, magnets, electronics, or wheels must still fit. Check the Pipe Schedule For plain, unlined pipe: Pipe ID = OD – 2 × Wall Thickness ASME B36.10 standardizes dimensions for welded and seamless wrought steel pipe.[4] ASME B36.19 covers welded and seamless wrought stainless steel pipe.[5] The following rounded nominal values show how much Schedule can change the bore: Pipe Size Schedule 40 ID Schedule 80 ID ID Difference NPS 4 About 102.3 mm About 97.2 mm About 5.1 mm NPS 6 About 154.1 mm About 146.4 mm About 7.7 mm NPS 8 About 202.7 mm About 193.7 mm About 9.0 mm NPS 12 About 303.3 mm About 288.9 mm About 14.4 mm An NPS 8 valve with a 198.0 mm finished bore creates different conditions depending on the adjoining pipe: Schedule 40 pipe ID is about 202.7 mm, so the valve creates a reduction. Schedule 60 pipe ID is about 198.5 mm, so the difference is small. Schedule 80 pipe ID is about 193.7 mm, so the valve bore is larger than the pipe bore. The NPS 8 Schedule 40-to-valve change is: Diameter Reduction = 202.7 – 198.0 = 4.7 mm Radial Step = 4.7 ÷ 2 = 2.35 mm The diameter decreases by about 2.3%, but the flow area decreases by about 4.6%: Area Reduction = 1 – (198.0 ÷ 202.7)2 ≈ 4.6% Area reduction helps explain the change in flow path, but it does not replace the pig supplier’s mechanical passage limits. Record the pipe data separately on both sides of the valve: Item Upstream Downstream Pipe OD Schedule or specified wall Measured wall Calculated nominal ID Measured end ID Lining thickness Internal seam height Ovality Do not assume that both sides are identical. A mainline valve may connect standard-wall pipe to a heavy-wall station spool, launcher connection, forged pup, or replacement section. Include Linings and Deposits For a uniformly lined pipe: Finished ID = OD – 2 × Wall Thickness – 2 × Lining Thickness A lining occupies space on both sides of the diameter: Lining Thickness per Side Total Bore Reduction 0.5 mm 1.0 mm 1.0 mm 2.0 mm 1.5 mm 3.0 mm 3.0 mm 6.0 mm For example, a 500 mm machined valve bore with a uniform 1.5 mm overlay becomes: Finished ID = 500 – 2 × 1.5 = 497 mm If the pig requires a 499
How to Select Ball Valve Pressure Class at Elevated Temperature | ASME B16.34 Derating, Design Conditions
Select the ball valve pressure class by checking every real design pressure and metal-temperature pair against the correct ASME B16.34 material table. After the shell rating passes, confirm that the seat, packing, body seals, maximum differential pressure, body cavity, flange joint, and actuator also pass. Class 150 does not mean 150 psi, and Class 300 does not mean 300 psi. The class number identifies a pressure-rating group. The allowable working pressure changes with material and temperature. ASME B16.34 covers pressure-temperature ratings, materials, dimensions, tolerances, examination, testing, and marking for covered flanged, threaded, welding-end, wafer, and flangeless valves.[1] A correct selection needs three separate checks: Shell rating: Can the body, closure, and other pressure-containing parts hold the internal pressure at the design metal temperature? Seat rating: Can the seats seal against the maximum pressure difference across the closed valve? Complete-valve rating: Can the packing, body seals, stem, bolting, end connections, and actuator work under the same conditions? A valve may pass the ASME B16.34 shell check but still be unsuitable because its seat, seal, or actuator limit is lower. Know the Units Use one pressure unit and one temperature unit throughout the calculation. Do not mix gauge pressure with absolute pressure. Value Equivalent 1 MPa 10 bar 1 bar 100 kPa 1 bar About 14.504 psi 10 bar About 145 psi 300°C 572°F 400°C 752°F NIST lists 1 psi as 6,894.757 Pa, which gives approximately 14.504 psi per bar.[2] Common pressure labels include: bar(g) or psig: Pressure above local atmospheric pressure bar(a) or psia: Pressure measured from absolute vacuum Differential pressure: Pressure difference between the two sides of the closed valve For example, 10 bar(a) is not the same as 10 bar(g). Near normal atmospheric pressure, 10 bar(a) is approximately 9 bar(g). Set the Design Conditions Do not select Class 150, 300, or 600 from normal operating pressure alone. List every pressure and metal-temperature combination the valve may experience. ASME B31.3 contains requirements for process piping used in refineries, chemical plants, hydrogen facilities, pharmaceutical plants, semiconductor plants, cryogenic plants, and related processing facilities.[3] Condition Pressure to Check Temperature to Check Normal operation Normal line pressure Normal valve-body temperature Maximum operation Highest operating pressure Temperature at that pressure Startup Maximum startup pressure Startup metal temperature Shutdown Trapped or equalized pressure Shutdown metal temperature Pump shutoff Suction pressure plus shutoff head Fluid temperature at shutoff Compressor settle-out Equalized system pressure Settle-out temperature Blocked outlet Maximum upstream pressure Temperature during blockage Steam-out Steam supply pressure Steam-out metal temperature Regeneration Regeneration pressure Regeneration temperature Heat tracing Pressure in trapped fluid Maximum traced metal temperature Relief event Required relief-case pressure Temperature during relief Minimum temperature Pressure during cooling or depressurization Lowest metal temperature For steam applications, also check steam state, tracing temperature, cleaning temperature, seat material, packing, and bolting. See this guide to sizing a ball valve for steam service. Record Time and Frequency Temperature alone does not describe the full service. Record how long the valve stays at each temperature and how often the condition occurs. The following is an example operating profile, not a universal industry requirement: Condition Temperature Duration Example Frequency Normal operation 300°C Continuous 8,000 hours per year Startup 200°C 2 hours 30 times per year Steam-out 400°C 4 hours 6 times per year Cooling 300°C to 50°C 6 hours 30 times per year A seal that survives six four-hour steam-out cycles may not be suitable for continuous operation at 400°C. Thermal cycling can also change gasket compression, seat contact, packing friction, and actuator torque. Keep Conditions Together Pressure and temperature must be checked as pairs that occur at the same time. For example, a line may have: 20 bar(g) at 150°C during startup 12 bar(g) at 350°C during normal operation 6 bar(g) at 420°C during steam cleaning Check these three pairs separately. Do not combine 20 bar(g) with 420°C unless that condition can actually occur. The highest pressure may occur at a temperature where the material still has a high allowable pressure. The highest temperature may occur when the system pressure is low. Neither value automatically controls the class. A useful comparison is: Shell utilization = Design pressure ÷ Allowable pressure at the same temperature The result must not exceed 1.00. The condition with the highest utilization is the controlling shell-rating condition. This ratio is a comparison tool, not an ASME formula. Utilization Meaning 0.50 Design pressure uses 50% of the allowable pressure 0.85 Design pressure uses 85% of the allowable pressure 0.98 The numerical margin is small and input uncertainty needs careful review 1.00 Design pressure equals the allowable pressure Above 1.00 The selected class fails that condition There is no universal rule that every valve must stay below 80% or 90% utilization. Any required extra margin must come from the project specification, owner, or governing design rules. Use Metal Temperature ASME pressure-temperature ratings apply to the pressure-containing metal, not automatically to the bulk fluid temperature. The valve body may be heated or cooled by: Steam tracing Electric tracing Insulation Sunlight Radiant heat from nearby equipment Stagnant fluid Thermal stratification Heat transfer from a vessel or furnace Rapid depressurization A closed bypass valve near a hot vessel may become hotter than the flowing main line. A traced valve can remain hot after process flow stops. For example, the process fluid may normally be 280°C while an external tracing system can heat an isolated valve body to 320°C. The pressure-temperature check should use the credible valve-body temperature for that condition. Find the Design Pressure Normal operating pressure is only one input. The valve may see higher pressure during pump shutoff, compressor shutdown, relief, static liquid head, or blocked-in heating. Pressure Source Data Required Normal Source Pump shutoff Suction pressure, shutoff head, fluid density, elevation Approved pump curve Compressor settle-out Connected volumes, initial pressures, temperatures Process calculation Static liquid head Fluid density and elevation difference Equipment layout Relief event Set pressure, permitted accumulation, backpressure Relief calculation Utility connection Maximum utility supply pressure Utility specification Blocked-in heating Trapped volume, fluid, heating range,
How to Verify Ball Valve Wall Thickness and Corrosion Allowance | Drawing Review, Material Loss, Design Margin
To verify ball valve wall thickness, calculate the minimum required wall at each critical location, include the specified corrosion allowance, account for manufacturing tolerances and machining, and compare the result with the lowest confirmed measurement at the same location. For an in-service valve, use current thickness, historical readings, damage shape and an approved retirement thickness to decide whether the valve can remain in service. ASME B16.34 covers pressure-temperature ratings, materials, dimensions, tolerances, examination, testing and marking for new cast, forged and fabricated valves.[1] API Specification 6D may also apply to ball valves used in petroleum and natural-gas pipeline or piping systems.[2] For valves installed in process piping, ASME B31.3 may control the connected piping system, including its materials, components, design, fabrication, examination, inspection and testing.[3] In-service valves within an API 570 piping circuit should be inspected under the applicable API 570 and API RP 574 requirements.[4] Set the Design Basis Do not start by comparing an ultrasonic reading with a value taken from an uncontrolled table. First confirm the exact valve and service conditions. Information What to confirm Why it matters Valve size NPS or DN Changes body dimensions and internal geometry Pressure class Class 150, 300, 600, 900, 1500 or 2500 Identifies the pressure-temperature rating group Design pressure Maximum specified design pressure Controls the required pressure capacity Design temperature Maximum and minimum design temperatures Changes material rating and low-temperature requirements Body material Exact material specification, grade and product form Affects rating, corrosion resistance and inspection response Body design Cast, forged, fabricated or fully welded Changes tolerances, machining and possible thin areas Ball support Floating or trunnion-mounted Changes the critical bores and pressure-boundary sections Port design Full bore or reduced bore Changes the ball port, body cavity and seat-pocket dimensions Corrosion allowance Internal, external, both or none Defines the additional sacrificial metal Standard edition Edition stated in the purchase contract Prevents requirements from different editions being mixed A pressure class is not one fixed pressure. The allowable pressure changes with material and temperature. Use the material, design temperature and design pressure to confirm that the selected class is suitable. Then determine the wall requirement for each pressure-containing location. The valve structure also changes the review. A forged floating ball valve normally requires close checks behind both seats and around the stem bore. A forged trunnion-mounted ball valve also has upper and lower trunnion bores, bearing pockets, drain passages and seat-injection passages. If essential records are missing: Do not assume a standard corrosion allowance such as 3 mm. Do not automatically use the newest standard edition. Do not use a catalogue image as the manufacturing drawing. Do not treat nominal drawing thickness as an original measurement. Do not calculate corrosion rate from readings taken at different positions. Define the Thickness Values A ball valve can have different requirements at the seat pocket, stem bore, drain passage and end connector. Each value should therefore be linked to a specific location. The letter i below represents one defined location. Symbol Meaning tstandard,i Approved pressure-design minimum at location i CAi Corrosion allowance that applies at location i trequired,i Required finished wall at location i tdrawing,i Nominal wall shown on the drawing tfinished-min,i Lowest wall allowed after tolerances and machining tactual,i Lowest valid measured wall at the same location tretirement,i Approved in-service retirement thickness When the project requires corrosion allowance to be added outside the pressure-design minimum: trequired,i = tstandard,i + CAi This formula applies only when the purchase specification clearly requires the allowance as additional metal. Confirm that it applies to the component and surface being reviewed and that it has not already been included in the manufacturer’s minimum wall. Example: Pressure-design minimum: 18.0 mm Specified corrosion allowance: 3.0 mm Required finished wall: 21.0 mm A finished wall of 20.6 mm remains 2.6 mm above the pressure minimum, but it is 0.4 mm below the full project requirement. Corrosion allowance is useful for predictable wall loss. It should not be treated as protection against stress-corrosion cracking, hydrogen damage, fatigue, deep pitting or severe cavitation. For H2S-containing oil and gas production and natural-gas sweetening environments within its scope, ISO 15156 covers the selection of cracking-resistant metallic materials.[5] Review the Drawing Use the approved sectional manufacturing drawing. Confirm its number, revision, valve model, size, class, material, bore type and purchase-order item. Mark every pressure-containing part: Main body End connector or closure Stem housing Lower trunnion housing Drain, vent and injection bosses Body joints and pressure-containing welds Flanged, threaded or butt-welded ends Then locate the shortest metal path between the pressure surface and the outside surface. The main centerline section is rarely enough. Critical sections normally include: Behind the upstream and downstream seat pockets Around the stem bore Around the lower trunnion bore Between the body cavity and drain passage Between the body cavity and vent passage Below sealant-injection passages Between seal grooves and the pressure cavity Near bolt holes close to the cavity At end-piece necks and weld-end transitions At repaired or ground areas An angled drain or injection hole can create a diagonal minimum ligament that does not appear on the main section. Normal-beam ultrasonic testing measures along the sound path and may not find the shortest diagonal distance. Use controlled drawing geometry, coordinate measurement, radiography, computed tomography or another qualified method when required. For threaded ports, check the largest material-removal diameter created by the internal thread root, counterbore, thread relief, entry chamfer and tapered profile. The nominal opening alone may overstate the remaining metal. The body cavity may also be larger than the ball port. A full-bore valve should not be reviewed only from the pipeline bore. Check the flow port, ball cavity and seat-pocket diameter separately. The main structural differences are also discussed in this high-pressure API 6D forged ball valve overview. Check the Drawing Margin Convert nominal drawing dimensions into the lowest permitted finished wall. tfinished-min,i = tdrawing,i − permitted negative tolerance − additional machining This is a simplified one-dimensional calculation. Core shift, forging eccentricity and forming reduction may need separate
Ball Valve Is Fully Closed but Flow Continues—Is It Seat Damage or an Actuator Travel Error
Short answer: first confirm that fluid is really passing through the valve. Then check whether the valve stem and ball reached the correct closed position. If the ball stops early, inspect the actuator travel, stop settings, coupling, energy supply, and valve torque. If the ball reaches the correct position but measured leakage remains, inspect the seats, ball, seat springs, rear seals, and pressure direction. A control-system Closed signal only shows that a switch or position sensor has changed state. It does not prove that the ball is fully seated. Actuator travel error and seat damage can also happen together. A ball that stops slightly early leaves a narrow opening that can erode the seat. A swollen, dirty, or damaged seat can also raise torque and prevent the actuator from completing its travel. About the data in this article: numerical examples such as pressure, time, current, angle, and leakage rate show how field records can be interpreted. They are not universal acceptance limits. The correct limit must come from the valve datasheet, actuator manual, project specification, and applicable test standard. Safety: do not loosen the actuator, coupling, packing, body bolts, drain plug, vent plug, or pipe connection while pressure or stored actuator energy may remain. Isolate every energy source, lock it out, depressurize the system, control spring energy, drain or purge the fluid, and verify isolation before work starts. OSHA requires stored or residual energy to be relieved, disconnected, restrained, or otherwise made safe before servicing.[1] Fast Diagnosis Finding Most useful next check Downstream pressure stays stable Trapped pressure, temperature change, or instrument response Downstream pressure continues rising Seat leakage, bypass flow, reverse flow, or another open connection A small approved travel correction reduces leakage Limit switch, stop setting, coupling, calibration, debris, or worn seat The valve closes without pressure but stops early under pressure Insufficient actuator output or excessive valve torque The actuator moves farther than the valve stem Coupling slip, worn adaptor, damaged key, spline, or internal drive The stem reaches the correct position but leakage remains Seat, ball, seat spring, rear seal, or seat-loading problem Leakage changes when pressure direction is reversed Directional seat design or damage to one seat The problem started after welding, flushing, or startup Rust, weld slag, scale, sand, or construction debris These findings are clues, not final proof. Do not increase actuator torque simply to force the valve closed. Extra torque may reduce leakage for a short time while cutting a soft seat, twisting the stem, damaging the coupling, or chipping a hard coating. Confirm the Leak Before removing the valve, identify what type of leakage is present: Through-seat leakage: fluid passes between the ball and seat into the opposite side of the pipeline. External leakage: fluid escapes through the stem packing, body joint, flange, vent, drain, or pressure-containing wall. Cavity discharge: fluid already trapped inside the valve body leaves through a drain or bleed connection. Cross-flow: fluid reaches the downstream pipe through a bypass, check valve, common header, or connected machine. ISO 15848-1 covers external leakage from valve stem seals and body joints. It does not set the through-seat leakage limit for a closed ball valve.[2] For external and internal leakage differences, see how to troubleshoot a leaking ball valve in the field. Record upstream pressure, downstream pressure, fluid temperature, valve position, pump status, and time after closure. One pressure reading is not enough. Stable downstream pressure: pressure may simply be trapped. Pressure rising toward upstream pressure: new fluid is entering the downstream section. Pressure rising with temperature: trapped liquid may be expanding. Pressure changing when another valve moves: a bypass, common header, or connected unit may be involved. Illustrative pressure trend: Time After Closure Upstream Pressure Downstream Pressure Fluid Temperature 0 minutes 10.0 bar 0.3 bar 24°C 5 minutes 10.0 bar 0.9 bar 24°C 15 minutes 9.9 bar 2.1 bar 25°C 30 minutes 9.9 bar 3.4 bar 25°C This example shows that fluid is entering the downstream section. It does not show the exact leakage rate because the downstream volume, fluid compressibility, pipe expansion, and connected equipment are not known. Do not judge leakage size only from the speed of pressure rise. The same leak can produce a fast pressure rise in a small closed volume and a slow rise in a large pipe or vessel. Walk the actual piping and check manual bypasses, automatic recirculation lines, check valves, warm-up lines, drains, vents, instrument tubing, flushing lines, temporary hoses, parallel equipment, and three-way valves. Change one condition at a time. If closing another valve stops the flow, another path is involved, but the original valve may still require a separate seat test. Also check the flowmeter. Zero offset, electrical noise, vibration, gas bubbles, a partly filled pipe, density compensation, blocked impulse lines, or operation below the meter’s reliable range can create a false low-flow reading. Compare the signal with downstream pressure, tank level, collected liquid, pipe temperature, or another calibrated instrument. Identify the Valve Record the valve model, size, pressure class, seat material, pressure direction, actuator model, and fail action before testing. The diagnosis changes with the valve design. Floating ball: pressure moves the ball slightly toward the downstream seat. Many soft-seat designs also use initial seat preload for low-pressure sealing. Trunnion-mounted ball: upper and lower supports hold the ball while movable seat rings press against it. Soft seat: provides tight shutoff but can be cut, extruded, swollen, softened, or permanently deformed. Metal seat: suits many hot or abrasive services but can suffer scoring, galling, coating loss, corrosion, or erosion. Control ball valve: may have a specified allowable shutoff class rather than an isolation-valve zero-leakage requirement. A typical soft-seated trunnion ball valve may use self-relieving SPE seats, DPE seats, or a mixed arrangement. These configurations do not react to cavity and line pressure in the same way. ISO 14313:2025 covers the design, manufacture, materials, assembly, testing, documentation, and process control of covered pipeline valves. It supplements API 6D, 25th edition, for its stated scope.[3] The actual seat action must still
