How to use a blind plate and where to apply it
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When first starting to learn design, the common types of blind flanges are the eight-character shaped ones or round steel plates. So, in what situations are blind flanges needed when installing pipes? I searched online but found no examples of situations where blind flanges must be used under specific conditions. The function of a blind flange is to prevent the medium inside the pipe from flowing backward. After some thought, I came up with several situations where blind flanges are necessary to block the pipe: 1. For spare connections – these are provided for future equipment. In such cases, it would be better to use a valve; the valve can remain closed, and once the subsequent equipment is connected through the valve, it can be opened to allow flow. If a blind flange is used, the medium inside the pipe would need to be drained first before the blind flange can be removed to connect to the subsequent equipment, which would result in downtime – isn’t that troublesome? 2. At the end of the pipeline, where there is no further equipment to connect to. In this case, a flange cover or a welded pipe cap can be used to block the end. A flange cover seems to be a better option, as it allows the pipe to be cleaned if the medium becomes dirty, or it can be used as a spare connection for other equipment. In my opinion, draining the medium inside the pipe is necessary when installing or removing blind flanges, which in turn leads to downtime. Since the 8-character blind plate definitely has some use, it’s not clear in what situations it should be applied; please discuss and offer your suggestions
It’s not necessary to shut down the machine when installing blind plates
Why is an 8-shaped blind plate installed behind the drain valve of the equipment or pipeline shown in the diagram? Isn’t it troublesome to use a blind plate for switching? What’s wrong with using only a valve for control?
Firstly, blind plates are of two types; one is fixed-type. It is mainly used for process replacement and switching during normal production. Another type is electric. It is mainly used for various users in the process branches, and cutting is carried out during production. For electric blind valve installations in a process flow, electric butterfly valves should be placed before and after it. Since butterfly valves may have issues with internal leakage and not sealing properly, it is necessary to close the blind valve first, then release the tightening device for the electric blind valve. After the valve has been operated (opened/closed), the tightening device should be used to secure it again; thereafter, the blind valve can be opened or kept closed depending on the production requirements. The above explanation is purely imitation and for reference only.
The 8-character blind flange has several advantages: 1. It provides an intuitive indication of the open or closed state. Conventional blind flanges require tags, but in complex sites, those tags are very easy to get lost, you know. 2. Quick replacement. If it’s a regular case, you still need to fill out a form to request the item from the warehouse, then check whether it meets the requirements, after that transport it to the site and carry out loading/unloading. For the 8-character sequence, just turn your head. 3. It has better sealing performance than valves. 4. I’ll add it later when I remember. It is not necessarily necessary to shut down the system in order to install or replace a blind flange, as the process conditions during pipeline operation must be taken into account during design; there are always cut-off fittings or valves near the blind flange. Near shutdown, just replace the blind flange. A blind plate is another name for a flange cover, and an 8-shaped blind plate is just one type of flange cover.
Can’t just use valves to shut off the flow? If one valve doesn’t work, use two; it’s unlikely that both valves will leak at the same time. Blind flanges do provide good sealing, but isn’t it troublesome to have to remove and reinstall the bolts?
A blind flange is added here to prevent internal leakage of the valve. The function of an 8-character blind flange is to enable opening and closing operations; if only a single blind flange is used, when it is necessary to make changes later, removing the blind flange results in too large a gap between the flanges, which hinders sealing
In terms of sealing performance, valves are inferior to flange covers. You can imagine how many potential leakage points there could be even in just a ball valve.
If it needs to be drained completely, then the bolts have to be loosened so that the blind plate can be turned around, the bolts tightened again, and then the valve opened. This method ensures good sealing, but it’s quite troublesome. Is this procedure only necessary when the medium inside the container or pipe is a hazardous substance and any leakage must be avoided? If the medium is water or non-hazardous, there’s no need for such a complicated process of installing a blind plate
If strict separation requirements do not apply, then considering the use of a dual valve is an option. In some operating conditions, such as those involving leaks, which can lead to dangerous accidents, blind plates are necessary