There are several people out there who have misunderstood the term double block and bleed valves and find it very difficult to describe the functions of the valves. It seems that each and every valve buyer as well as manufacturers has a different view of the meaning of the term when selecting valve, and this can lead to a wrong type or specification of valve. There is also confusion in the oil and gas industry as a result of the definition which was given by two credible sources. Another confusion started when some people used them as double block and bleed and they are in need of a valve which has the capabilities of double isolation and bleed, the director of application engineering, Ron Manson explained the differences with respect to the definition and terms which are essential when it comes to the most appropriate valve to be used in a particular system.
Whenever an individual or an engineer says that he or she is in need of DBB, this depends on the experience and application of what is considered as DBB valves with respect to theexplanation given by the Engineer and Process Valves manager. Based on the need of the customer and their preferred kind and application of valve, we can then provide the kind of valve which will be perfect for use for the user and the engine.
The major thing which is needed by a user whenever they mention a double block and bleed valve which has a compact design or a valve system which provides isolation that is reliable in situations which are critical rather than a single valve. This double block and bleed valve will help in the reduction of installation footprint;this would save the additional requirements and enhance the reduction in the weight in crucial areas. All these would help in saving time, cost as well as space.
According to the definition which was given by the pipeline valves manufacturers, a double block and bleed is a single valve which has two seating surface that are in a close position and ensures the pressure is sealed from both ends of the valves by providing a cavity in between the seating surfaces. It is also noted in this definition that whenever one side is under pressure, a positive double isolation will not be provided by the valves.
However, the Federal regulation (OSHA) describe double block and bleed valve as the closure of a pipe by closing and locking, two in-line valves and, locking or opening a vent valve which are in the line between the two valves which areclosed.
You cannot achieve the same kind of isolation with the definition of API and OSHA. The API willallow DBB valve to be a single valve with two seats which are unidirectional, while you can achieve the OSHA standard with the aid of two separate valves with a method to bleed pressure in between them. Some valves make use of a twin valve design and this involves the combination of two different valves into a single body, the design of a twin valve reduces the weight as well as the potential leaks paths and would also meet the requirement for a double block and bleed valve.
The valve associations usually choose to follow either of the OSHA’s or API’s definition, but some people have created their personal definition which is being used in their own definition for industry terms. For instance, the association of Actuator and the British Valve defines it as a manifold which brings together one or several isolation valves, this can be a ball valves and several vent into a single assembly which is interfaced with morecomponents such as switches, pressure gauges as well as transmitter which is used for measuring pressure.
A single valve is required for DBB capabilities because it’s not a system. The traditional techniques which was previously used by engineers has been replaced by double block and bleed valve so as to obtain the desired configuration in the pipeline, and this can be achieved by making three different valves with the aid of flanges, associated bolting as well as Tee pieces.
A double block and bleed valve can provide isolation in both the downstream and upstream direction as well as in situation where there is temperature and pressure. Isolation is very essential in situations where leakages via a valve could result to several consequences. Once you successfully isolate the fluid, you can easily drain the space which is between the two seating surfaces or valve. This is essential for the maintenance and checking the integrity in situations where leakages can be checked properly.
This kind of valve helps in the replacement of the traditional techniques which are in existence and are used by engineers so as to create the desired configuration i.e. (double block and bled) in a pipeline. Conventionally, so as to realize a double block and bleed configuration, two different isolation valves would be installed by the engineers as well as a differentplace for bleeding the cavity in between. The space is usually at a premium in the environment of the refinery and this approach requires an additional valve unit which need to be installed and a “T”-junction which would provide space for the cavity to bled more than double of the space required when it is compared with a single valve system. The increase in size can make the installation not feasible, especially in a situation where several valves are to be upgraded along the line.
The tracking of the emissionis very high on the agenda for valve end user. Multiple challenges are presented by the emission, not only that the loss of a valuable media via leakage carry an economic cost, but the emissions likewise contribute significantly to air pollution as well as climate change. Also, the emissions of compounds which are volatile can result to a long term health risks for the communities, employees and the escape of the flammable substances can increase the risk of explosions. While the volume of medium escaping from a particular leak may be small, the cumulative effect across a large facility can add up to a great proportion of thetotal emissions of plant. The seal which is placed between two separate pieces of material represent a path where leak can occur and can thus increase the number of different parts of pipe for the installation of valve would increase the chances of media escaping from the system.
When the three valves are incorporated into a single housing, it would enhance the safety of the system by removing connections which separate the units, thereby resulting in minimal potential leaks paths in the system. There are two different ball valves which are contained in this unit and it helps to delivers 100% tight shutoff with the aid of plastic or metal seats which are coated withtungstenbased chrome carbide. The space which exists between valves is reducedand this give the operator chance to remove the space and also establish a safe isolation within a short duration and this would serve as a major benefit in an emergency situation. The reduction in volume of the materials which is removed from the valve likewise implies less waste, lower costs, reduced handling as well as easier disposal.
The increase in the activity in the offshore sector of the energy industry has resulted to an additional factor which has to be considered whenever designing piping systems. The space in these modern locations is always at its best and the design of piping systems and the component which is associated must be in a compact design. There are structural constraints which are very essential and help to keep the structure as light as possible, and there are several advantages which can be obtained from making the component smaller and lighter. The job which are done in a construction site are likewise expensive and limit the installation manpower. This situation has resulted to the changes in the patterns of the component of valve components so as to saveweight, space as well as labor cost where applicable, and at the same time retaining the original function of the valve. The greatest savings would be observed in the reduction of leak to the atmosphere due to the fact that the potential leak points are minimal when compared to the conventional design.
The process isolation philosophy has also become more complex because there is need to address safety issues as well as the requirement for double block and bleed isolation which has become more commonly used. Two in-line valves is needed by the double block and bleed isolation and this is utilized to drain the fluid which is trapped in between the two elements that are closed.
The double bleed and block valve helps in saving space, cost, and likewise provide zero leakage capabilities from upstream to downstream. The valve likewise aids in the integrity check of seat seals. Apart from these functions, the double bleed and block valves can be used in a variety of markets and applications like LNG, petrochemicals, storage and transmission, marine and manifold valves in pipelines, natural gas industrial processes, products transmission lines which are refined.
Double block and bleed valves are utilized in areas where critical isolation is needed so as to ensure there is no leakage in the system. Based on the application and type of service, several types and options of double block and bleed valves are available to fit specific needs. For instance, in liquid service which is close to municipalities or waterways, double-expanding gate valves with double capabilities are preferred for isolation which is critical because they provide, upstream and downstream simultaneously as well as mechanical seal which is not affected by variation in pressure or vibration.
Anthony Carrea, the product manager at gate valve said that whenever they teach sales force and customers about double block and bleed valves, the API definition is mostly used, in his presentation he usually explain that a double block and bleed valve is a valve which has two seats and whenever it is closed, it will seal against pressure from the two sides of the valve thereby allowing the body cavity to be bled.
Another application of the double block and bleed valve is that it is perfect for use in the meter calibration market. Each and every closed valve in the meter system must be properly sealed. This is due to the fact that a small leakage in the system can lead to an error in the calibration of the meter and such will affect the operation. This can result to a huge amount of money for end users, choosing the appropriate API verified double bleed and block valve can help in ensuring correct calibration each and every time.
The action of the mechanical wedge of double block and bleed valve compresses both the downstream and the upstream seals firmly against the body of the valve, require no help from the pressure line to affect a positive seal. In the transmission and storage market, the double block and bleed valve are commonly used and they helps to effect a consistent as well as zero leakage in the sector.
Whenever you are trying to determine the definition of double block and bleed valve to follow, whether it’s that of OSHA or API, it is essential to understand the differences and similarities which exist in the kind of block and bleed valves and where it will be applicable. In addition to that, it is essential for the valves to have the features which is required for the isolation and should be tested properly in the factory.
Due to the fact that DBB has become a generic term in the industry, it is essential to consider the application, media as well as various environmental challenges whenever you want to choose the perfect solution as well as valve type.