3.3 Valve types, parts, accessories and application,

Gate valve
Application: on/off. Usually use for complete isolation.
Typical serviceable parts: Stem, seat, wedge
Types: Solid wedge, flexible wedge, split wedge.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, packing.

Image Source: profmaster.blogspot.com

Globe valve
Application: throttling. Usually used for throttling liquid flow. Large pressure drop across due to significant change in direction in design.
Typical serviceable parts: Stem, disc, seat, packing.
Types: Angle, Y-type, straight type.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, packing.

Image Source: www.globalspec.com  /  Mcgraw-hill Publishing

Needle valve
Application: throttling. This valve is exactly like globe valve, except with a tapered seat. For more info, see globe valve above.
Typical serviceable parts: Stem, disc, seat, packing.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem.


Diaphragm valve
Application: on/off. Usually used for very corrosive chemicals to protect valve trim.
Typical serviceable parts: Stem, disc, diaphragm.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, diaphragm

Image Source: www.globalspec.com

Ball valve
Application: throttling or on/off. Usually use for quick opening with less torque requirement.
Typical serviceable parts: stem, handle, ball, seat.
Types: straight, angle, L-port, T-port
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, body connection type, L/T port arrangement, design/material of the body, ball, seat, stem.

Image Source: www.kitz.co.jp

Plug valve
Application: See ball valve, except that a turnable plug with a bore is used instead of a ball.


Butterfly
Application: throttling or on/off. Not suitable when opposite sides of fluid have large differential pressure, makes the valve hard to open, not tight sealing.
Typical serviceable parts: Stem, disc, seat, packing.
Types: wafer type, lug type.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, packing.

Image Source: www.kitz.co.jp

Check valve
Application: Non-return flow.
Typical serviceable parts: Disc/ball, seat
Types: Swing Disc, lifting disc, butterfly, ball,
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, swing/lift/flap arrangement, design/material of the body, disc, seat.

Swing type check valve

Image source: www.kitz.co.jp

Lift Type Check Valve (Similar to globe, but w/o a stem)

Image source: www.jdvalves.com

Safety valve 
Note: Usually referred to many as PSV (Pressure Safety valve for gas systems, opens when overpressure detected) or PRV (Pressure relief valve for liquid systems, opens based on proportion of overpressure)
Application: Pressure relief or thermal relief application. Selection based on pressure and flowrates usually sized according to API 520 PSV Sizing. ASME Section I & Section VIII also denotes their required settings for allowable tolerance on set pressures and blow down(closing back pressure)
Typical serviceable parts: Lever, spring, adjusting ring, disc, seat, bellows.
Types: Conventional, Balanced pressure, Pilot operated, Power operated,
What to specify when buying: ASME Section I (w/ Lever, open bonnet, 2 adjustment ring configuration with U stamped for boilers), ASME Section VIII (Any configuration with UV Stamped for general process), Other design (with or without lever, open or closed bonnet, with or without bellows(back pressure compensation).) , Pressure rating, temperature, flow rates, process medium, end connection type, design/material of the body, disc, seat, stem,

Typical ASME Type I PSV.

Image source: Consolidated Catalogue Type 1900.

Image Source: spiraxsarco.com

Detail of PSV with Bellow/diapgragm

Image Source: spiraxsarco.com

Pneumatic Actuator - variable control

Pneumatic Actuator - on/off control
Air being a more powerful actuating media suitable for explosive environment, is also used for on off control of a valve by an piston actuator.
It comes with a solenoid valve which allows air into itself, the electrical component(solenoid valve) is smaller and less costly to own, as compared to having a huge electrical component with hazardous area protection which could cost significantly more.

Solenoid Actuator - Usually used for on/off control, for where quick opening and closing of the valve is required. Used on small systems, or when used for saving cost on pipelines which requires explosion proof set up(see Pneumatic Actuator above).

Motorized actuator - Usually used for on/off control, for where more torque is required to actuate the valve, motor can be powered by electrical power, hydraulic power or pneumatic.

Handwheel, handle, disc, seat, bonnet - See above photos on valve description for a clearer picture.
The bonnet-body of these valves could be integral or separable. Advantage to be separable if the valve is costly to purchase as replacement. ie. Exotic material or CTE/BAM tested are very costly to purchase, disadvantage is that the leak sealing will not be as robust.

Spoke wheel pulley - Used where valves are installed in high location, where access is inconvenient.

Extended spindle - Used on cryogenic systems, where high humidity leads to icing which eventually ices up the entire handwheel, as such denying user from operating the valve. A long handle alleviates this problem.

Pressure rating - American systems, 150#, 300#, 600#.... sometimes it may denote 600WOG instead which is equivalent. WOG stands for water, oil gas. Read the post on Piping Specs for details on how pressure rating come about.


Valve Sizing for pressure loss (liquid)
dP = SG * (41720Q/Cv)^2

dP = Pressure loss (kPa)
SG =  Specific gravity (dimensionless)
Q = flowrates (m^3/s)
Cv = Coefficient of flow (check valve specification from manufacturer)

For gas/steam, use its specific formula for Cv.


What to specify when buying
The above will help you the understand a valve. With regards on how to specify a purchase to the procurement or vendor when sourcing for valves, refer to the short write up on this section:
3.2 Valve Spec & Purchase

For each of these valves, the essential details to be knowledgeable to select the right valve for the right application. If in doubt, consult manufacturer's application engineer for advice.

3.1 Piping specifications

Piping specs

What are these? Whenever a plant is designed to run a certain process, piping to carry fluid will be involved. This spec will be developed by the piping engineer for any user to reference and select the specified pipe material, thickness, rating and many for the fluid service in future. The content of piping specifications varies through out different contractors, so dont worry if one item is missed out, however the critical ones shall be present.

If there are no company standard piping specs available and one needs to be specifically developed for the project, it should preferably be developed from an existing database for similar services. If otherwise consult the experienced materials , reliability, maintenance and operations specialists, the more the merrier to eventually form the most probable opinion based on experience to mete it on trueform.

This is a vital document for the following activities during projects, so have it ready during the early periods of the design phase in a project.
P&ID & Detailed engineering - Specifying pipes, fittings and indication of line numbers
Equipment list - Specifying line code number, valve code numbers
Proj QC - Verification on conformance to codes
Maintenance - Specifying pipe and fitting replacement
and many more.

What information to look for or include in the piping specs

These are what you would normally find on the piping specification table from top to bottom

1. Fluid service

• Types of process fluid this specification can handle, the number of fluids are not limited in each pipe spec, to reduce the pages! 

2. Flange pressure rating and type

• The ratings are derived usually from ANSI or DIN/ISO data tables, select one that could meet the pressure and temperature specified on the PFD or design specifications.

3. Design temperature/pressure of the pipeline

• This may not be necessary to include as it may confuse designers with equipment design temp/press. This item needs to be verified with thickness calculation and process engineers to minimize change logs.

4. Corrosion allowance

• This is derived from corrosion rates for similar pipe material and process fluid from existing data. Corrosion allowance(mm) = Corr. Rates(mm/yr) X Plant Design Life(y)

5. Pipe material

• This is usually specified in its ASTM name, so procurement could use them to source accurately, suppliers will understand in an instant. Eg. CS ASTM SA106, Gr. B SMLS refers to Astm code 106 grade B seamless carbon steel pipe. 
• The pipes comes in std length of 6m. Other lengths are also available but uncommon and subjected to increased lead time. 

6. Pipe size and thickness

• This will come in a table format, as pipe sizes and thickness will vary to meet design pressure requirements. It is developed from the calculations in ASME B31.3 process piping codes: t=[PD/2(SE+YP) +tc+tf ] x [100/(100-tf)]

t= Thickness of pipe, in

P=Design pressure, psi

D= OD of pipe, in

S=Yield strength of pipe at design temperature, psi (Based on material)

E=Weld efficiency, dimensionless (from 0.85 to 1 depending on joint method)

Y= Derating factor, dimensionless (usually 0.4 for steel material below 900F)

tc = Corrosion allowance, in

th = Thread depth, in (If threaded connections are used)

tf = tolerance factor, dimensionless (Usually 12.5% depending on pipe maker)

• If designing for pipeline projects, you may refer to B31.4 for less stringent calculation, for marine systems refer to ABS/LR/DNV or the class design codes, as calculations may differ. However the principles remains the same. 

7. Fitting size and rating

• Similar to pipe calculations but different calculations, will be specified in a specific post in future.

8. Flange size, spec and rating

• Specified type of flange and its rating to meet required pressure requirement at its design temperature. 
• Type of flange face and joint to equipment/pipes, will be specified in a specific post in future. 

9. Valve size, specs and rating

• There are different valve material, types and configuration for each range of the sizes.  Select the suitable type for the service, ie. On/off, throttling, low pressure loss, quick opening, etc. Explain on later posts.

10. Brand connection types & its fittings.

• Different size pipes(run) may use different joints types which offers similar strength at a lower cost. Reason being a socket type joint on. 1" pipe may be strong, but not on a 4" pipe. The recommended connections are specified in the last section
• Tees are used for same size connections.
• Reducing tees for a reduced branch
• O-lets, weld type, socket type, thread type allows to stub on a pipe to the main with better strength.
• Stub in, most economical way of connecting branch pipes.
• stub out for one size smaller branch

Sample piping specification for reference to the above explanations.
Source: ligo.org

1.0 Welcome

Welcome to this blog. This will be my first blog to document my personal knowledge for future reference, you may also use it for your reference too. The interpretations for some codes would be solely based on my opinions unless references are made, we could still trash things out, feel free to leave either positive comments or debates, most importantly facts or industry believed assertions are documented for benefit of everyone reading this.

There should be posting at least weekly or fortnightly on topics related to process plant piping and static equipment which is related to my current scope of work. It will mainly cover design, operations and reliability issues i deal with or have read through other references.

I hope to also include some topics on statutory requirements in Singapore in the future posts, as some guidelines remain ambiguous and probably this blog could shed some light on these matters.

Avoid debates on english and grammar, as it wasnt the intention of this blog, this thought was echoed from when we often find clients and contractors picking on "grammatical errors" to delay approval process on document submissions which could be rather annoying.