Distinguishing between blind and blank flanges is a critical requirement for operational safety and efficiency within industrial applications such as pipe systems and networks.
These two terms, blank and blind, are often used interchangeably; however, it is important to note that they do represent specific functions and requirements, and these distinctions matter.
Both provide a sealing solution that closes off areas to prevent liquids and gases from escaping; however, due to their key closure difference, they affect isolation, capping, testing, and safety differently, all areas which we will explore further throughout this post looking at blind flange vs blank flange.
We will also look at the gasket relationship and how the effectiveness of the seal closure also depends on the sealing face. For example, a flat face is often used in pipes or valves to prevent the flange from cracking when bolted; however, ring-type joint gaskets are the most suitable choice for ultra-high-pressure applications.
What is a blind flange?
A blind flange is a bolted closure with no bore and is most typically used to seal off pressure vessel openings or close pipe systems. A solid face with bolt holes around the perimeter allowing you to match it to the mating flange.
The blind flange can be permanent or semi-permanent and raised or flat face. This type of flange is able to withstand significant pressure and high mechanical stress, meeting ASME B16.5 compliance standards and B16.47 for larger sizes.
A blind pipe flange is one that is used to close off the end of a pipeline that is no longer in use. This can be used as a temporary seal allowing for testing, additional piping systems to be added without running the risk of leaks or contamination, or for safety reasons while systems are being repaired.
Construction: disc-shaped with bolt holes around the perimeter that allow them to be quickly bolted/welded in place.
Face and gasket: raised-face blind flanges will take a ring gasket, whereas, alternatively, a flat-face blind flange takes a full-face gasket.
Typical use: used in oil and gas, petrochemical, water treatment, and power generation.
Materials: this type of flange is available in carbon steel, alloy, copper, aluminium, and stainless steel.
What is a blank flange (line blank/spade)?
Alternatively, a blank flange in the line-blank or spade sense is a solid plate which is inserted between flanges for temporary isolation during maintenance or testing. Often part of a spade-and-spacer or spectacle-blind set, these flat, circular flanges have no bore and hence block the flow of gas or fluid from escaping.
Blank flanges can be manufactured from a range of materials and meet ASME B16.48 standards.
These flanges are durable but suited to more low-pressure applications.
Blind flange vs blank flange at a glance
There are some notable differences between piping blank vs blind flanges, most notably their use, i.e., permanent versus temporary distinction. The table below highlights the key differences and critical information.
| Attribute | Blind flange | Blank flange (line blank / spade) |
| Purpose | To close a pipe end, valve or vessel opening | To temporarily isolate a line for maintenance or testing |
| Permanence | Permanent or semi-permanent | Temporary; removed after the task, ie maintenance, repairs |
| Form | Bolted flange, bolt holes, no central bore | Solid plate inserted between two mating flanges |
| Standard | ASME B16.5 (B16.47 for large sizes) | ASME B16.48 (line blanks, spades and spacers) |
| Face and gasket | Raised face takes a ring gasket; flat face takes a full-face gasket | Sealed each side by a gasket when inserted between flanges |
| Typical use | Capping unused nozzles, terminating a line | Positive isolation and lock-out for safe maintenance |
| Materials | Carbon steel, stainless, alloy, and others | Compatible with the piping material |
How to choose between them
Your decision on whether to opt for a dummy flange vs blind flange should be based on the requirement, i.e., do you require permanent termination? Opt for a blind flange. Whereas if you’re carrying out temporary maintenance and require isolation and a lockout, opt for a blank flange or spade.
Again, if you require a flange suitable for high-pressure ratings, look at a blind flange and make sure to check fluid compatibility and material suitability across both.
Benefits of blind flanges:
- Offer high structural integrity, offering high strength in high-pressure environments
- Durable
- Easy to install and remove
- Corrosion resistant
- Versatile
- Provide a permanent leak-proof seal
Benefits of blank flanges:
- Flexible
- Prevents liquids and gases from escaping
- Cost-effective
- Act as a secure, temporary safety barrier
- Preserves and supports the integrity of the sealing surface
- A valuable, temporary solution.
How SSP can help
At Specialist Sealing Products we specialise in providing both blank flanges and bolted slip blinds, gaskets, and flange isolation products.
All meeting high standards and industry regulations, to find out more or to receive a quote, call us on 01535 274 776.
FAQ
Q1. What are the differences between a blind flange and a blank flange?
A blind flange is a bolted closure that permanently or semi-permanently seals a pipe end or vessel opening. A blank flange, or line blank, is a solid plate inserted between two flanges to isolate a line temporarily for maintenance or testing.
Q2. Is a blind flange permanent?
It is treated as permanent or semi-permanent. These flanges are bolted and removable for access, but they are specified and rated for long-term closure, unlike a temporary blank.
Q3. Can a blank flange be used permanently?
No, this is not recommended. Blank plates are intended for temporary isolation; for permanent termination, a certified blind flange rated to ASME B16.5 is the correct choice.
Q4. What gasket do you use with a blind flange?
This depends on the flange face. For example, a raised-face blind flange takes a ring gasket, whereas, alternatively, a flat-face blind flange takes a full-face gasket.
Q5. What standards cover blind and blank flanges?
Blind flanges follow ASME B16.5 and B16.47 in larger sizes. Line blanks, spades, and spacers are covered by ASME B16.48.
Read the next article: Ring Type Joint vs Raised Face
