Learn about the different types of valves used in the oil and gas industry and their differences: API and ASME gate, globe, check, ball, and butterfly designs (manual or actuated, with forged and cast bodies). Briefly said, valves are mechanical devices used in piping applications to control, regulate and open/close the fluid’ s flow and pressure. Forged valves are used for small bore or high-pressure piping applications, cast valves for piping above 2 inches.
WHAT IS A VALVE?
The different types of valves used in the petrochemical industry suit any of the following applications:
- Start/stop the flow of the fluid (hydrocarbons, oil & gas, steam, water, acids) through the pipeline (example: gate valve, ball valve, butterfly valve, knife gate valve, or plug valve)
- Modulate the flow of the fluid through the pipeline (example: globe valve)
- Control the flow of the fluid (control valve)
- Change the direction of the flow (for example a 3-way ball valve)
- Regulate the pressure of a process (pressure reducing valve)
- Protect a piping system or a device (pump, motor, tank) from overpressures (safety or pressure relief) or back-pressures (check valve)
- Filter debris flowing through a pipeline, to protect equipment that may be damaged by solid parts (y and basket strainers)
(Source: Spirax Sarco)
A valve is manufactured by assembling multiple mechanical parts, the key ones being the body (the outer shell), the trim (the combination of the replaceable wetted parts), the stem, the bonnet, and an actioning mechanism (manual lever, gear or actuator).
Valves with small bore sizes (generally 2 inches) or that require high resistance to pressure and temperature are manufactured with forged steel bodies; commercial valves above 2 inches in diameter feature cast body materials.
The valves’ market is worth approximately 40 billion USD per year in 2018, and major manufacturers are located in the US, Europe (Italy, Germany, France, and Spain), Japan and China.
Valves used in the oil and gas industry and for piping applications can be classified in multiple ways:
VALVES BY DISC TYPE
- LINEAR MOTION: gate, globe, diaphragm, pinch, and check valves
- ROTARY MOTION: butterfly, ball, plug, eccentric- and swing check valves
- QUARTER TURN: devices that require approximately a quarter turn motion, from 0 to 90° of the stem to move from fully close to a fully open position or vice versa.
|Oil & Gas Valve Types||Linear motion valves||Rotary motion valves||Quarter turn valves|
|Lift check valve||X|
|Tilting-disc check valve||X|
|Stop check valve||X||X|
|Safety valve / Pressure Relief Valve||X|
VALVES BY BODY MATERIAL
- CAST (the body is obtained by casting steel). The main casting materials for valves are listed in this article.
- FORGED (the body is manufactured by forging steel)
VALVES BY TYPE OF ACTUATION
- MANUAL: the valve is operated manually, via levers, wheels and/or gears;
- ACTUATED: the valve is actioned via electromechanical devices, called actuators, that may be electric, pneumatic, hydraulic and gas over oil
VALVE BY DESIGN
- GATE VALVE: This type is the most used in piping and pipeline applications. Gate valves are linear motion devices used open and close the flow of the fluid (shutoff valve). Gate valves cannot be used for throttling applications, i.e. to regulate the flow of the fluid (globe or ball valves should be used in this case). A gate valve is, therefore, either fully opened or closed (by manual wheels, gears or electric, pneumatic and hydraulic actuators)
- GLOBE VALVE: This type of valve is used to throttle (regulate) the fluid flow. Globe valves can also shut off the flow, but for this function, gate valves are preferred. A globe valve creates a pressure drop in the pipeline, as the fluid has to pass through a non-linear passageway.
- CHECK VALVE: this type of valve is used to avoid backflow in the piping system or the pipeline that could damage downstream apparatus as pumps, compressors, etc. When the fluid has enough pressure, it opens the valve; when it comes back (reverse flow) at a design pressure, it closes the valve – preventing unwanted flows.
- BALL VALVE: A Ball valve is a quarter-turn valve used for shut-off application. The valve opens and closes the flow of the fluid via a built-in ball, that rotates inside the valve body. Ball valves are industry standard for on-off applications and are lighter and more compact than gate valves, which serve similar purposes. The two main designs are floating and trunnion (side or top entry)
- BUTTERFLY VALVE: This is a versatile, cost-effective, valve to modulate or open/close the flow of the fluid. Butterfly valves are available in concentric or eccentric design (double/triple), have a compact shape and are becoming more and more competitive vs. ball valves, due to their simpler construction and cost.
- PINCH VALVE: This is a type of linear motion valve that can be used for throttling and shut-off application in piping applications that handle solid materials, slurries and dense fluids. A pinch valve features a pinch tube to regulate the flow.
- PLUG VALVE: Plug valve is classified as a quarter-turn valve for shut-off applications. The first plug valves were introduced by the Romans to control water pipelines.
- SAFETY VALVE: A safety valve is used to protect a piping arrangement from dangerous overpressures that may threaten human life or other assets. Essentially, a safety valve releases the pressure as a set-value is exceeded.
- CONTROL VALVE: these are valves to automate complex petrochemical processes.
- Y-STRAINERS: while not properly a valve, Y-strainers have the important function of filtering debris and protect downstream equipment that may be otherwise damaged
To make sure that valves of different manufacturers are interchangeable, the face to face dimensions (i.e. the distance in mm or inches between the inlet and the outlet of the valve) of the key types of valves have been standardized by the ASME B16.10 specification.
ASME B16.34: VALVE COMPLIANCE
The ASME valve standard B16.34 is a globally accepted standard to design, manufacture and test valves used in the oil and gas industry. ASME B16.34 is also mentioned in the more general ASME spec ASME B31.1, “Power Piping Design”.
Back in 1988, the scope of this standard was modified to include threaded-end and weld-end valves in addition to flanged-end valves.
A valve complies with ASME B16.34 when the following conditions are met:
- The valves body & shell materials comply with ASME and ASTM material standards for chemistry and strength
- Body & shell materials are heat-treated to ensure proper grain structure, corrosion resistance, and hardness.
- Wall thicknesses of body and other pressure-containing components meet ASME B16.34 specified minimum values for each pressure class.
- NPT and SW end connections comply with ASME B1.20.1 or ASME B16.11.
- Stems are internally loaded and blowout proof.
- All bolting will be ASTM grade with maximum applied stress controlled by B16.34.
- Each valve is shell tested at 1,5x rated pressure for a specific test time duration.
- Each valve is tested for seat leakage in both directions for a specific test time duration.
- Each valve is permanently tagged with materials of construction, operating limits and name of the manufacturer.
A control valve is used in the oil and gas industry to regulate the flow rate of the fluid in a pipeline or process (and the related process parameters as pressure, temperature, and level) according to signals managed by a controller. The role of a flow control valve in the complex petrochemical process is key, as the multiple loops involved in the process should be kept under strict and dynamic control to make sure that the process, as a whole, works as intended and produces the desired output in terms of quantity, quality and time.
The application of flow control valves is increasing in the last years, due to growing process automation in most industries.
These type of valves are used in irrigation systems, water treatment plants, oil and gas plants, power generation, fire prevention systems, food processing industries by streamlining the response to changes in processes and providing greater safety to personnel and equipment.
A flow control valve used in the oil and gas industry can have a globe, butterfly, or ball shape, and is available in multiple material grades and sizes. The most used type of actuator is the air-operated, as it involves less ancillary equipment (as cabling, switchgear) when compared to other types of actuators.
The opening and closing of the valve and its regulation are done by the combined effect of an electronic controller, a positioner and the actuator of the valve (which can be electric, pneumatic or hydraulic).
The actuator opens and closes the control valve in response to changes in key process parameters, such as changes in pressure, level, temperature, and flow.
By such action, the process parameters are maintained within the required target range to make sure the process, as a whole, works as intended and produces an end product in the desired quantity and quality.
FLOW CONTROL VALVE COMPONENTS
The main components of a control valve are:
- the valve body: where the modulating element is contained and operates
- the positioner: which is the element to control the degree of the valve opening and is mounted on the body of the valve
- the actuator: is the device that is used to move the modulating element of the valve, for example, the ball (ball valves), the disc (butterfly) or the stem (globe valves)
- the controller
FLOW CONTROL VALVE ACTUATORS
The selection of actuators is based on the required thrust of the rod and the movement of the valve.
Engineers must determine if the diagram or piston actuator is the most suitable type. Actuators are the primary energy source used to move and position the flow control element within the valve body.
A variety of types are available, including pneumatic, electric, hydraulic, electro-hydraulic and manual. Pneumatic actuators are the most widely used for throttling applications.
Considered the standard for automatic control for more than a century, three types of pneumatic actuators are available: piston, spring-and-diaphragm, and rotary vane. The first two can be adapted for use on either rotary or sliding-stem valves; the latter is used only on rotary valves.
FLOW CONTROL VALVE ACCESSORIES
Normally, the selection of accessories such as positioners transducers, boosters, solenoid valves, limit switches, handwheels and travel stop, snubbers, regulators, transmission lines, is based on engineering specifications.
Cost is a major factor in material selection.
Not just the cost of material in dollars per pound, but also the cost of fabrication and inspection contribute to the uninstalled cost of the valve. Installed cost includes not only the cost of installation but also the cost of any damage from improper installation and costs the inspection.
The latter consists of such things as analysis of material chemistry, radiographic and surface examination of castings and welds, and check to see that the installed valve is the correct one and that it is properly oriented.
The selection of the appropriate or optimal control valve type depends on the particular study of the pipe system and the conditions of its fluid, but the size of the control valve should be such that pressure drops through it and not the drop of pressure of the pipe is the one that controls the flow.
All valves, including steam control valves, are designed to meet an allowable internal leakage standard (FCI / ANSI). The higher the number of leaks, the lower the permissible internal leakage rate.
A Class I valve will have the highest internal leakage rate and usually the lowest cost; While a Class VI valve will have the lowest allowable internal leakage rate. Steam valves must be specified to have a leak rate of not less than Class IV. A class IV steam control valve will maintain a long service life.
FLOW CONTROL VALVES TYPES
Control valves can be classified into two main types, based on the stem movement:
- Linear motion/reciprocating: globe (straight, angle, 3-way), diaphragm and, pinch control valves
- Rotary stem: ball, butterfly and, plug control valves types
Globe control valves can be either single or double seat.
CONTROL VALVE SELECTION
Process engineers must consider many factors to select the correct control valve. The general criteria to be considered for selection are summarized below:
- Type of control; the degree of control; the degree of shutoff.
- Design temperature; design pressure; allowable pressure drop.
- Fluid corrosivity; fluid erosion properties; other characteristics, such as fouling or coking.
- Inherent characteristics, such as valve Cv: degree of hazard from leakage; heat or cold conservation; cost.
As the design criteria are known, process engineers can proceed to make a selection of the correct type of control valve and related equipment, as well as the material of the valve itself.
The next step is to create the detailed specification (generally drafted by a specialized piping engineer) and create a purchase specification describing the valve for suppliers.
The specification should contain, as minimum: a description of the type of control valve (rotary, sliding); bore size and pressure rating; end-connections; type of body joints; material specification for body components, trim, gaskets and bolting; positioner and controller requirements; a reference to an industry design standard for type of valve.
Generally, a computerized system help engineers determine the most suited control valve and its features based on process parameters.
CONTROL VALVES INSTALLATION
- Always expand the discharge steam line piping at least one pipe diameter. It is not uncommon to expand the discharge piping at least two or three pipe diameters. It should be noted that the expansion of the pipe reduces the valve outlet velocities thus prolonging the valve life. The valve manufacturer will provide the appropriate pipe size after the control valve. Match the pipe size to the heat transfer inlet connection.
- The distance after the steam control valve should be at least ten pipe diameters before the inlet connection of any heat transfer. In pressure reduction applications at least 20 horizontal pipe diameters must be left before a change of flow direction.
- The control valve must always be installed in a horizontal vapor line, never vertically.
- It is more important to properly select the valve at low flow operating conditions that at its assumed high flow operating conditions.
- Bypass valves must be used in the control valve installation. The by-pass valve is used to allow the personnel of the industrial facility to operate the process without the control valve if valve failure or maintenance reactive, preventive and predictive.
- Installing pressure gauges before and after the steam control valve allows the line diagnostics in real time. The importance of proper installation cannot be overstated. In many cases, the source of a troublesome startup can be traced to a control valve that is not properly installed. It is strongly recommended that personnel with an instrumentation background be used at least to supervise the installation and setup of control valves.
HOW TO ORDER A VALVE
Manufacturers of valves used in the oil and gas industry need to know the following information to supply the right device:
- Valve type
- Bore size in NPS or DN
- Valve pressure rating (class range from 150# to 4500#)
- Specification (example API 6D, API 600, API 602, etc)
- Body and trim materials (at least)
- Required end connection (flanged, threaded, butt weld, lug and others)
- Fluid in the pipeline (>oil, gas, water, steam, solids)
- Working temperature and pressure
- Delivery time
- Origin restrictions (Chinese and Indian origins allowed or not)
EXAMPLE HOW TO ORDER OIL & GAS GATE, GLOBE, CHECK VALVES
Each manufacturer has own valves ordering sheets that map the valve configuration parameters that user has to consider:
GS – F – 6″ / 150 – 316 – B
1 2 3 4 5
|1. Valve type||2. End type||3. Size / Class||4. Body Material||5. Options|
|C: Check Valve|
CL: Lift Check Valve
CS: Check pressure Sealed Valve
CW: Swing Check Valve
G: Gate Valve
GG: Forged Gate Valve
GL: Light Type Gate Valve (API 603)
GS: Gate Pressure Sealed Valve
O: Globe Valve
OB: Globe Bellowed Sealed Valve
OS: Globe Pressure Sealed Valve
|F: Flanged End|
T: Threaded End
W: Butt Weld End
S: Socket Weld End
|Size: NPS 1/2 – 80″|
10K: JIS 10K
|GG: Forged Gate Valve|
316: Casting S.S CF8M
304: Casting S.S CF8
F316: Forgings S.S F316
F304: Forgings S.S F304
WCB: Steel WCB
LCB: Steel LCB
HB: Hastelloy B
G: Gear Operator