Types of blinds in refinery and selection

During refinery production and maintenance, blind flanges are critical equipment for isolating pipelines or equipment and shutting off media flow. Selection of blind flanges depends on operating conditions (pressure, temperature, and media corrosivity) and isolation requirements (temporary/permanent, frequent switching/fixed blocking). We will introduce common blind flange types in refineries based on their structure, material, and pressure rating:

I. Classification by Structural Shape to Adapt to Different Isolation Scenarios

This is the most commonly used classification system in refineries. Blind flanges of different shapes have significant functional differences, which directly determine their installation methods and applicable scenarios.

1. Flat Blind Flange: A circular flat plate with no central hole and bolt holes on either side that match the flange. It seals against the pipeline flange using gaskets and is secured with bolts to achieve isolation. It is suitable for pipelines operating at atmospheric, low, or medium pressures (≤4.0 MPa) and with media that do not experience strong erosion (such as crude oil, refined products, and circulating water). Its advantages are simple structure and low cost. However, its disadvantages are that it requires separate storage after disassembly, which reduces efficiency during frequent switching. Depending on the flange size (e.g., DN50, DN200) and pressure rating, the sealing surface is typically either flat (FF) or raised (RF), and is used in conjunction with a gasket (e.g., asbestos gasket, spiral wound gasket).

2. Spade blinds are thin, rectangular or circular steel plates (thickness calculated based on pressure) without bolt holes. They require an “8-shaped blind plate gasket” or a dedicated flange clamp. The plate is inserted between the flanges and secured with flange bolts to achieve a seal. They are suitable for temporary isolation or frequent switching (e.g., when quickly shutting off a pipeline section during equipment maintenance). Their advantage is easy disassembly (no need to completely remove flange bolts; simply loosen and remove the plate). However, their disadvantage is that sealing reliability depends on the clamping force, making them unsuitable for high-pressure or high-vibration applications.

3. The Figure-8 Blind Flange has a shape similar to the figure “8,” with one side consisting of a solid blind plate (blocking end) and the other end featuring a flow-through orifice (or circular hole), connected by a narrow strip. Bolt holes are integrated throughout the flange for direct connection, allowing for rotation to switch between “blocking” and “flow-through” positions. It is suitable for pipelines that frequently switch between “isolation” and “flow-through” (e.g., feedstock pipelines in catalytic cracking units and sour gas pipelines in desulfurization units). The blind plate can be switched between these positions by simply loosening the bolts and rotating it 180°, eliminating the safety risk of incorrect or missing blind plates (a major safety hazard in refineries) and reducing valve usage (the flow-through end can replace some shut-off valves). The Figure-8 Blind Flange is the preferred blind plate for isolating high-risk media in refineries (e.g., hydrogen, hydrogen sulfide, and liquefied petroleum gas). The strength of the “figure-8” connection should be regularly inspected to prevent breakage due to vibration.

II. Classification by Material to Adapt to Different Media and Operating Conditions

Refineries operate with complex media (including crude oil, acid gas, high-temperature steam, catalyst dust, etc.). Blind plate materials must meet heat, corrosion, and pressure resistance requirements. Commonly used materials are as follows:

1. Carbon steel (Q235, 20#): Temperature resistance ≤ 450°C, neutral media resistance, not acid and alkali resistance, suitable for conventional crude oil, refined oil, circulating water, and steam pipelines (non-corrosive conditions).

2. Stainless steel (304, 316L): Temperature resistance ≤ 800°C, acid, alkali, and salt spray resistance (316L is resistant to chloride ions), acidic water, hydrogen sulfide (H₂S), sour crude oil, and solvent oil pipelines.

3. Alloy steel (16Mn, Cr-Mo steel): Temperature resistance ≤ 600°C, high strength, and high-pressure resistance (16Mn is resistant to medium pressure, Cr-Mo is resistant to medium pressure). High-pressure resistant), hydrogenation unit (high-pressure hydrogen), atmospheric and vacuum unit (high-temperature heavy oil) pipelines.

4. Copper alloys (brass, bronze): Low-temperature and seawater corrosion resistant, with excellent sealing properties. Suitable for low-temperature media (such as liquefied petroleum gas) and circulating seawater cooling pipelines.

5. Non-metallic materials (PTFE, graphite): Strong corrosion resistance (such as concentrated acids and strong alkalis), temperature resistance ≤ 260°C (PTFE), suitable for low-pressure corrosive media pipelines (such as acidic wastewater treatment pipelines).

III. Classification by pressure rating to match pipeline pressure requirements.

The pressure rating of the blind plate must strictly match the nominal pressure (PN) of the pipeline to avoid leaks or ruptures caused by pressure incompatibility. Common pressure ratings in refineries are as follows:

Atmospheric pressure blind plate (PN ≤ 0.1 MPa), atmospheric pressure tank breather valve pipelines, vent lines.
Low-pressure blind plate (0.1 MPa < PN ≤ 1.6 MPa), circulating water, steam tracing, and product pump outlet pipelines.
Medium-pressure blind plate 1.6MPa＜PN≤10MPa, for catalytic cracking unit fractionator feed lines and atmospheric unit overhead lines.
High-pressure blind plates: 10MPa＜PN≤100MPa, for hydrocracking unit reaction system lines (high-pressure hydrogen) and reforming unit lines.
Ultra-high-pressure blind plates: PN＞100MPa, for special high-pressure test lines (rarely used in refineries, mostly in scientific research).

IV. Refinery Blind Plate Selection and Safety Criteria

Figure-8 blind plates are preferred: For high-risk media (H₂, H₂S, LPG) or pipelines with frequent switching, figure-8 blind plates prevent “blind plate management failure” (e.g., missing blind plates leading to media crosstalk) and are recommended by safety regulations.
Material Verification: For corrosive media (such as sulfur-containing wastewater), spectral analysis is required to confirm the blind plate material (e.g., whether 316L meets the standards) to prevent corrosion perforation caused by incorrect material usage. Clear Labeling: All blind plates must be labeled with “number, pressure rating, material, and intended use.”

In summary, the selection of blind plates for refineries must focus on “safety isolation and adaptability to operating conditions,” integrating the three key factors of structure, material, and pressure, while strictly adhering to safety regulations to effectively prevent risks such as media leakage, fire, and explosion.

Safety Tip: It is strictly forbidden to use ordinary blind plates in place of figure-8 blind plates. The installation locations of hollow rings and solid plates must be strictly distinguished to avoid the risk of system pressure buildup or leakage.

In addition to using various types of blind plates, you can also consider upgrading the blind plates to line blind valves, which can reduce manpower and improve efficiency.

For example:

19 sets of DN100 8-shaped blind flange need to be switched every 2-3 days
Before the upgrade: 3-4 people need to work for 5-6 hours to complete switch
After the upgrade: Only 1 person needs to work for 1.5 hours to complete switch

10 sets of DN100 8-shaped blind plates need to be switched every 7 days
Before the upgrade: 3 people need to work for 5-6 hours to complete the switching
After the upgrade: only 1 person needs to work for 0.5-1 hour to complete the switching

ZZJG Valve provides the above information on types of blinds in refinery and selection. If you want to know more about blinds valve types and selection, please contact us via WhatsApp or email.