Ball valve is a 1/4 turn valve with 0-deg to close and 90-deg to open. It uses ball as main flow control component. It's a position sealed valve with 2 - 4 deg tolerance for proper close/open. Mainly used for on/off application across many industries, available in flow control application (3-way ball, V-port ball etc)
Due to its useful design ball valves are preferred in many on/off application across industry for its durability, ease of maintenance, availability & reusability. Depending on the design and material, ball valve can support up pressure as high as 1000 bar and temperatures up to 500°C. Typically size range from 0.1 to 48 inches (could be bigger).
Advantages of 1/4 turn
Straight flow valves give low pressure drop
Lower torque to operate (reduce cost on actuator)
Operate at faster speed.
Minimize fugitive emissions at the stem
Reduce maintenance on stem packing
Features of Ball Valve
Suitable for pigging service.
Fast operation suitable for ESD (Emergency Shutdown)
Full bore provides high flow rate.
Secondary sealant injection as temporary sealing for damages seat.
The ball of a floating design are held in place by the valve seats, it utilize the upstream line pressure force to push the ball against the downstream seat for a proper sealing.
Under the maximum DP, this force can be too great for the seat material and subsequently increase the operation torque or damage the downstream seat. Hence floating design are mainly found in the low to middle pressure rating.
The ball are held in fix position by trunnion (Plate or Pin). The trunnion are normally installed with bearing to reduce the operation torque, hence trunnion design is suitable for high pressure and bigger size valve. The seats are floating and energize with springs to push the seat sealing face towards the ball and seal the valve. Double Piston or Single Piston effect seat can be used to provide Double Block and bleed or self relieving functions. In some slurry service, a special sealant is injected in the seat sealing surface to reduce torque, improve sealing and prevent further damage on the seat.
Full Bore & Reduced Bore
Full bore ball valve having almost zero pressure loss, with the valve bore sizethat is close to the pipe ID
Suitable for pipeline that requires to run pig, high flow rate application for transmission pipeline.
Reduced bore normally comes with one pipe sizes smaller than the valve size. Example: 12" x 10" OR 8" x 6"
The size reduction caused restricted flow/lower CV than full bore and the smaller valve body makes It's much cost effective compare with full bore. It's suitable for any application that doesn't required pigging.
One Piece Body
Blue colour section is the main body of the valve . The red colour insert holds the seats and ball in position within the valve body. Insert is typically screwed into the valve, hence the proper tightening of the insert is important not to over tighten and caused increase of valve operation torque or damage the seat. Under tightening might result in valve leaks.
One piece body reduced potential leak paths at the body compare to 2/3 piece design. Minimal influence by Pipeline stress. Due to the method used to assemble the body insert, single piece design (except fully welded & top entry) are normally available in small sizes.
Two Piece Body
The valve body are bolted together with a body & end piece.
Two-piece ball valves are generally available in floating ball configuration, however there is some manufacturer that produce with trunnion. This design is very popular in the petrochemical & refinery ranging from size 1/2 - 18 inch, class 150-600. It's not suitable for big size & higher rating since trunnion mounted 3 piece design is much cost effective.
It has only one leak path on the body compares to three piece design that has 2 leak paths.
Three Piece Body
One valve body with two end pieces are bolted or threaded together. Flexible design that allow different end connection in single body. Easy to maintain and assemble/disassemble. Most commonly used design in Oil & Gas industry for high pressure application upto API15K. Three-piece design is one of the most cost effective design to be manufactured and commonly stocked items.
Top Entry Body
The name top entry derived from how this valve is being assembled thru inserting the ball & seats from the top of the valve. The top of the valve are closed with a top flange, which makes top-entry valve serviceable/repair while the valve are installed in the pipeline. Top-entry ball valves are physically larger than 1/2/3 piece design the valve body are usually cast material (also available in forged block body)
Double Bloock & Bleed Ball Valve
A combination of two ball valves into a single body. Double block and bleed (DBB) design is becoming more popular on installation that requires DBB function but are constrained by space and weight limitation. Great saving on space and weight. Commonly used a the instrument header for smaller size, larger DBB are used for process size can be upto 30 inch Class 1500. Needle or ball valve are installed at the middle of the valve body for bleeding purpose.
Benefits of having a full bore ball valve within a limited space or area with weight constraint. Compact design offers weight, height and length saving compares with conventional ball valve ranging from 30% - 70% . Compact high pressure valves used in manifold for offshore and subsea application.
Fully Welded Body Designed to be a maintenance free valve for transmission pipeline that run thru rural area or buried service. The body in multiple pieces are welded together instead of bolted. Typically comes with sealant injection ports for regular flushing and greasing to pro-long the lifespan on the valve. Difficult to repair, to change the seat valve body needs to be cut. Welded body comes with cylindrical body and spherical body, spherical body offers some weight savings.
Basically almost all the different type of steels or alloys are used to manufacture ball valve. Depending on the process condition, availability and commercial viability of the selected material. Below are the types of steel / alloys that used by the industry.
Special Chrome or Nickel alloys: Petro Chemical , Off Shore Oil & Gas
Stainless steel: Petro Chemical, General industrial, Cryogenic applications
Carbon steel: Oil & Gas, General industrial, Low temperature applications
Brass: General industrial, Utilities & Water service.
Aluminium Bronze: Sea Water
Typical temp range
A very commonly used seat material. PTFE is a synthetic fluoropolymer an excellence material for valve seat due to its low friction, high chemical resistance (literally all chemical) & good temperature resistance. PTFE is vulnerable to Explosion Decompression (ED), it will expand violently and exploded (damage) when the high pressure is being remove rapidly. Hence PTFE is normally suitable for valve up to certain pressure class like class 150 - class 300.
-45°C to 232 °C
Reinforced version of PTFE with glass or carbon added into the virgin PTFE has increases the wear resistance and deformation under high pressure. Typically in 15% or 25% glass/carbon R- PTFE having similar chemical resistance to virgin PTFE. The added glass in R-PTFE will re-act to hydrofluroic acid and hot spring caustics, hence it's not suitable to use with these chemicals.
-100°C to 220 °C
PEEK (Polyether Ether Ketone) a high performance engineered thermoplastic it is consider to be a premium great material for valve seat. It offers great resistance to water and chemical, ability to continuously expose to hot water / steam. Suitable for temperature range from -56°C to 315°C. PEEK is suitable for high pressure application and corrosive service. For valve industry, it is normally being used for offshore oil & gas upstream sector. Due to PEEK rigid characteristic it increase the operation torque of the valve that uses PEEK seat. PEEK can be used from medical implants to nuclear service.
-56°C to 315°C
Devlon is considerably one of the toughest thermoplastic with excellence wear resistance and suitable for high pressure application in the market. It's produced by using the Spin casting / centrifugal casting method to achieve the higher material density that gives the material its characteristic. Devlon V-API is the Devlon grade that is commonly used as seat material for valve. This material has low moisture absorption rate that give its dimensional stability. Commonly used in the oil & gas offshore application that demand resistance to high pressure, corrosion and wear. Suitable for valve pressure from 300 to 1500.
-100°C to +150 °C
EPDM - ethylene-propylene diene monomer has good scratch and tear resistance. Offers good chemical resistance to variety of acid and alkaline. Subject to attack by oil, hence it's not suitable for oil application like petroleum, hydrocarbon, strong acid/alkaline. Not recommended for compressed air.
-29°C to 107°C
Viton a flurocarbon elastomer that are intrinsically compatible with a wide variety of chemicals. Because of its good chemical resistance, Viton are widely used in services like hydrocarbon, concentrated mineral acids and petroleum oil. However it's not suitable for steam or hot water service.
-17°C to 149°C
Buna-N (Nitrile rubber) is a synthetic rubber copolymer that has good resistance to oil, water & acid. It has good compression, scratch resistance and tensile strength. Buna-N is relatively not affected in services that is paraffin base like fatty acid, alcohols & oil. Not suitable for Nitric Acid and strong oxidizer service.
17°C to 121°C
Polyoxymethylene engineered thermoplastic manufactured by various manufacturer with different trade name and Delrin (Dupont) is more commonly used in valve application. It has high stiffness, low friction, excellent dimensional stability, low moisture absorption, high fatigue endurance, superior impact resistance. Commercially it is being use in many high performance component like ball bearing, ski binding, fastener, automotive and electronics products. Delrin has good resistance to cold flow, ideal for pressure up to 5500psi (depend on the size) Can withstands nuclear radiation at doses of up to 106 rads. Do not use on oxygen service, or steam.
-40°C to 150°C
Metal seat are used for valve in high abrasive, high temperature, high pressure or corrosive service. The seat and ball are coated using the various metal coating methods listed below to increase the metal surface hardness, wear resistance, corrosion resistance, fatigue strength and reduce friction. Metal seated valve can take temperature upto 800 deg C or more. The sealing face of the ball are lapped repeatedly to achieve tight seal, once lapped the sealing face will typical unique to each other.
Ball is floating and push by download pressure to seal the valve.
Seat supports and hold the ball in position.
Provide tight seal for the valve.
Cavity pressure relieving
Trunnion mounted ball valves - Seat Function
Seats are floating and energized by springs
Provide seat tightness
Body Cavity pressure relief
Double block & bleed
Ball Valve Seat Design
Pressure balancing seat.
At the earlier degrees during valve opening under high pressure, the seat will be expose to high stress and vulnerable to damage. When upstream seat being unload, the process media flows between the body and the seat, then above the seat and through the slots, behind the seat in the cavity. With this design the pressure are balanced to avoid possible damage of the seat and prolong the life of the valve.
Double Beveled Seat.
Double Beveled seal ring is design to reduce valve operation torque. Under low pressure condition, the seat surface in-contact with the ball are lesser which increases the sealing pressure between the surface (pressure = force/area). Under higher pressure condition, the entire seat surface are in-contact with the ball surface. The larger contacting area between seat and ball reduces the sealing pressure.
Cantilever seat design is good in reducing valve operation torque. Under higher pressure condition the ball will be pushed toward the seat and caused the seat to flex. This movement increases the sealing area between the ball and seat surface, then increase the sealing ability and reduce the pressure on the seat to prevent seat damage.
API SPEC 6D Specification that covers design, manufacturing, testing, documentation for Ball, Gate, Check and Plug valve. API6D is the most common design used from Production Rigs (Except Wellhead section), Onshore processing plant to Transmission pipeline, or in-short its right in-between Wellhead to Petrochemical plant.
Pressure Class: 150, 300, 600, 900, 1500, 2500
End Connection: Flange (RF & RTJ), BW, SW
Face to Face: per B16.10 (or per agreement) Key Guideline:
Lifting lug for valve 8" and above
clear indicator to show valve in open (inline with pipe) & close (transverse with pipe).
Requirements for non-destructive examination
Method and duration of testing (eg: hydro to 1.5 times of valve rating)
Anti static device for soft-seat and Anti static testing.
Automatic cavity-pressure relief
ANSI/API 608 (ISO17292 /BS 5351) Specification for flanged, butt-weld, socket-weld and threaded end Metal Ball Valves, the spec are additional requirements for ball valve that conformed to B16.34. The standard covers Class 150, 300, 600 & 800 metal ball valves only for use in on-off service. The spec was developed for standard ball valve used in Downstream segment like refineries and chemical companies. Key Guideline:
The force required to fully open/close valve cannot exceed 80 lbs.
Stem torque safety factor should be twice the operation torque published.
Requires adjustable packing glands.
The weakest part of ball to stem connection located externally.
"Hollow balls” are not allowed.
Antistatic on valve stem.
Valve tested per API-598.
ASME/ANSI B16.34 B16.34 is the most commonly accepted by end-users, engineering contractors, fabricators and valve manufacturers as the basis for valve design, valve testing and valve performance. It covers pressure-temperature rating, dimensions, tolerances, materials, NDT requirements and marking for cast, forged, flanged, threaded, and welding end, and wafer or flangeless valves. In fact, most of the valves produced for Oil, Gas & Petrochem industry these days meet or exceed the requirements of ASME B16.34.
Both most commonly used piping design standard, ASME B31.1 (Power Piping) and ASME B31.3 (Process Piping) refers to B16.34 for selection of VALVES. Key Guideline:
Shell tested at 150% of rated pressure for a specified test duration.
Anti blowout stem design.
Specified minimum valve body wall thickness.
Body material according to ASME and ASTM material standards.
Heat treatment for pressure containing parts of the valve.
API6A API 6A is standard used in wellhead and Christmas tree equipment which has stricter testing and manufacturing requirements that makes API 6A valves more expensive than others. API6A uses different pressure rating from AMSE or ANSI rating class, API 6A valves are pressure rated for. 2,000LB, 3,000LB, 5,000LB, 10,000LB, 15,000LB, and 20,000LB. Generally, the pressure rating for API 6A valves are higher than other standards. API are different from ANSI in material of construction and higher working pressure. An API 6A valve cannot be connected to ANSI flanges this may affects the overall working pressure rating. 6A PRESSURE RATINGS:
API 2000 (psi) => 13.8 MPa
API 3000 (psi) => 20.7 MPa
API 5000 (psi) => 34.5 MPa
API 10000 (psi) => 69 MPa
API 15000 (psi) => 103.5 MPa
API 20000 (psi) => 138 MPa
API 6A defines valve inside bore by exact ID (eg: 7’’ 1/16=179mm), not to be confuse wit nominal diameter of pipe (eg: 8’’, 10’’,12’’) hence It is important to check the corresponding diameters between API6A and pipe nominal diameter. Typical 6A Sizes
PRODUCT SPECIFICATION LEVELS (PSL)
FIVE PSL ARE DEFINED IN THE API 6A: PSL1, PSL2, PSL3, PSL3G, PSL4
These 5 PLS define different levels of technical quality requirements
API6A PSL QUALITY CONTROL REQUIREMENTS FOR VALVE SHELL (body, bonnet, end connector, flange):
API6A PSL QUALITY CONTROL REQUIREMENTS FOR VALVE BORE SEALING MECHANISMS (trim except stems):