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Double Block and Bleed Valve (DBB) Requirement (API, API RP, or other code)?
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(Petroleum)
(OP)
24 Aug 20 21:13In different Oil & Gas companies I have worked, engineers tend to say that any pressure rating from 600# and above, double block and bleed valves are required. Is there any API or similar code or RP that recommends the use of DBB at or above a pressure rating?
Is double block and bleed valve required for chemical injection line i.e. upstream the main process line?
Is double block and bleed valve required for sample lines line i.e. upstream the the sample collection point?
What is the best way to select the most appropriate DBB for the application?
Replies continue below
(Chemical)
26 Aug 20 15:29the partial pressure of H2S is another important parameter foe DBB. 600lb is very conservative for DBB. 600 lb is applicable only for sour services. DBB shall be used for sample connections.
(Mechanical)
30 Aug 20 23:57IMO, besides the H2S, injection chemicals, amines, etc., DBB may be used for the system isolation per high temperature as well as high pressure, maintenance of OTR or S/D activities.
(Petroleum)
7 Sep 20 14:26I don't believe there are any codes or official body standards that require this as each case is dependant on its own circumstances, company policies, procedures and philosophies.Over time the requirement for DBB has become established at certain levels of pressure and contents. Safety engineers have gradually upped the game and then everyone does what they did last time and on it goes.The terminology though is very confusing and often misunderstood.Officially a Double block and bleed valve is simply one which can seal in both directions with a bleed between each seat.What most people think DBB is is actually Double isolation and bleed (DIB). Sometimes you can accomplish this within one valve, but more commonly three valves are required (two main process and a bleed valve)It's up to the process and safety engineers to determine when you need greater certainty of isolation than that offered by a single valve.Usually manned entry into vessels requires positive isolation (i.e. blinds, removal of spool pieces, that sort of thing, not a valved off connection.There's no way to answer your question without knowledge of the contents, the pressure, your company / project isolation philosophy etc.There are small diamter single forging double valves, there are single ball valves with DPE seats, there are positive isolation split plug and gate valves which offer this within a single (usually quite expensive) valve such as Orbit twinseal plug valves and WKM split wedge gate valves amongst others. https://www.anwvc.com/line-card/general-twin-seal-... Although they call themselves DBB valves, they are also DIB valves due to the positive sealing of both faces.Some other reading here includes https://www.eng-tips.com/faqs.cfm?fid= and https://www.eng-tips.com/viewthread.cfm?qid= Remember - More details = better answersAlso: If you get a response it's polite to respond to it.
(Petroleum)
7 Sep 20 14:55Also this might help
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
(Mechanical)
27 Sep 20 06:31The following may be of interest:In particular Appendix 6.
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About double block ball valve
A double block and bleed (DBB) ball valve is a type of valve that provides two isolation barriers to ensure positive isolation of the downstream process fluids. This means that it has two separate sealing mechanisms which enable it to block both upstream and downstream flow, as well as provide a means to bleed any trapped fluid between the two seals.
DBB ball valves are commonly used in fluid handling systems where double isolation is required to prevent the mixing of different fluids or for maintenance purposes. They are widely used in industries such as oil and gas, petrochemical, and chemical processing. These valves are known for their reliability, safety, and ease of maintenance.
Double block ball valve advantages and disadvantages
Advantages of double block ball valve:
1. Double block and bleed functionality: The double block ball valve can provide two barriers to isolate fluid, making it safer for maintenance or repair work.
2. Reduced leak potential: With two seating surfaces, the chances of leaks are minimized, enhancing the valve's reliability.
3. Lower torque requirements: Compared to other types of valves, the ball valve typically requires less torque to operate.
4. Quick operation: The ball valve can be quickly opened or closed, allowing for efficient flow control.
Disadvantages of double block ball valve:
1. Cost: Double block ball valves can be more expensive than other types of valves due to their specialized design.
2. Limited flow control: While the ball valve is efficient for on/off control, it may not be as effective for throttling applications.
3. Potential for blockage: In situations where the valve is exposed to debris or particulates, there is a risk of blockage that can hinder its performance.
4. Size limitations: Double block ball valves may not be suitable for larger pipeline applications, as the size and weight of the valve can become a limiting factor.
Structures of double block ball valve
A double block ball valve typically consists of the following components:
1. Body: The main outer casing that houses all the internal components of the valve.
2. Ball: A spherical-shaped valve element that controls the flow of fluid through the valve. It typically has a hole through the center to allow or block the flow.
3. Seats: The seats are the sealing surfaces located on either side of the ball. In a double block ball valve, there are two sets of seats that provide double isolation.
4. Stem: The stem connects the handle or actuator to the ball, allowing for the opening and closing of the valve.
5. Actuator: The actuator is the mechanism used to control the operation of the valve, either manually (handwheel or lever) or automatically (pneumatic, electric, or hydraulic).
6. Seals and O-rings: These components are used to create a tight seal between the ball and seats, preventing leaks.
specific requirements and standards.
Double block ball valves are typically used in applications where double isolation is necessary to prevent leakage or cross-contamination between different process streams. Some common applications include:
1. Oil and gas industry: Double block ball valves are commonly used in oil and gas production, transportation, and refining processes to isolate pipelines and control the flow of various fluids.
2. Petrochemical industry: These valves are used in petrochemical plants to isolate different chemical processes, ensuring safety and preventing leaks.
3. Chemical industry: Double block ball valves are essential in chemical processing plants where the separation of different chemicals is critical to prevent reactions or contamination.
4. Water treatment plants: These valves are used to isolate different water treatment processes to maintain water quality and prevent mixing of treated and untreated water.
Overall, double block ball valves are ideal for applications that require reliable isolation and control of fluids to ensure operational safety and efficiency.
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