Super Guide: How to Calculate Blind Flange Thickness

How to Calculate Blind Flange Thickness

Super Guide: How to Calculate Blind Flange Thickness

Calculating the thickness of a blind flange is crucial for ensuring the safety and efficiency of piping systems. It’s a task that might seem daunting at first, but with the right approach, it becomes quite manageable. I’ve delved into this topic extensively, and I’m here to share my insights to make this process as straightforward as possible.

Understanding the factors that influence blind flange thickness, such as pressure, temperature, and material, is the first step. I’ll guide you through the calculations, breaking down the complexities into easy-to-understand concepts. Whether you’re a seasoned engineer or a newcomer to the field, you’ll find valuable information to help you determine the optimal thickness for your blind flanges.

What is a Blind Flange?

Before we dive into the calculations, it’s crucial to understand what a blind flange is and why it’s such an integral part of piping systems. A blind flange is essentially a plate that covers or seals the end of a pipe, ensuring no flow through that section. It’s a critical component for testing, isolation, and shutdown in various industrial applications.

In our previous article, we provided a detailed introduction to the method of blind flange pressure rating, which is also very important in engineering. We recommend that everyone should read it carefully.

My experience working with piping systems has shown me that the significance of a blind flange cannot be overstated. They are used not only for routine maintenance and repairs but also play a vital role in emergency situations to prevent leaks and hazardous spills. What makes them particularly special is their ability to be customized according to specific requirements, such as pressure, temperature, and the material of the pipeline they are intended for.

How to Calculate Blind Flange Thickness

Selecting the right blind flange for a project involves understanding material compatibility and the environmental conditions it will be exposed to. For example, stainless steel flanges are ideal for corrosive environments, while carbon steel is better suited for high-pressure scenarios. This adaptability is a testament to the blind flange’s importance in ensuring system safety and reliability.

It’s also worth noting that the installation of a blind flange must be done with precision. A poorly fitted blind flange could lead to leaks or pressure inconsistencies, risking the integrity of the entire piping system. Therefore, calculating the correct thickness for a blind flange isn’t just about ensuring its effectiveness; it’s also about upholding the highest safety standards.

In the next sections, we’ll explore how the parameters such as pressure, temperature, and material influence the thickness calculation. Each factor plays a pivotal role, and I’ll guide you through understanding how to integrate these into the final calculation. Remember, the goal is to equip you with the knowledge to determine the optimal thickness for your blind flanges, enhancing both safety and efficiency in your piping systems.

Why is blind flange thickness important?

When it comes to piping systems, ensuring the integrity and reliability of connections is paramount, which brings us to the significance of calculating the correct blind flange thickness. These components are crucial for managing the flow within pipes, especially when isolating sections for maintenance or in case of an emergency shut-off. Let’s delve into why proper calculation of blind flange thickness can’t be overlooked.

Ensuring Leak-Proof Connections

One of the key reasons for calculating the right blind flange thickness is to ensure a leak-proof seal. A blind flange that’s too thin might not withstand the force exerted by the fluid inside the pipe, leading to leaks. This could not only disrupt the system’s efficiency but also pose significant safety risks, especially if the fluid is hazardous. Accurate thickness ensures that the flange can maintain a tight seal under the operational conditions it’s subjected to.

How to Calculate Blind Flange Thickness

Withstanding Pressure and Stress

Another critical aspect is the blind flange’s ability to withstand the pressure and stress it’s exposed to during operation. The thickness of the flange directly influences its strength and, therefore, its ability to handle high pressure without deforming or failing. It’s essential to consider the maximum operating pressure and any potential stressors, including physical and thermal stress, to determine the optimal thickness.

Let’s move on to an exact calculation example to illustrate how we can determine the appropriate thickness for a blind flange in a practical scenario.

Calculation Example

Let’s calculate the thickness of a blind flange for a pipe operating under a maximum pressure of 500 psi and with an outside diameter of 24 inches.

The formula we’ll use is as follows:

[Thickness = \frac{ (Pressure \times Diameter) }{ (2 \times Material Strength \times Joint Efficiency + Pressure) }]

Assuming a material strength of 20,000 psi and a joint efficiency of 0.7, let’s put these values into the formula.

[Thickness = \frac{ (500 \times 24) }{ (2 \times 20,000 \times 0.7 + 500) }]

Calculating this, we find:

[Thickness = \frac{ 12,000 }{ 28,500 }]

[Thickness \approx 0.42 inches]

The minimum thickness required for the blind flange under these conditions is approximately 0.42 inches. It’s crucial to round this figure up to the nearest standard thickness available to ensure safety and compliance with industry standards.

How to Calculate Blind Flange Thickness

Factors to Consider

When I’m diving into the world of blind flanges, several critical factors come into play to ensure I calculate the thickness accurately. Understanding these factors can significantly affect the safety and efficiency of the piping system. Below, I’ll delve into some key elements that must be considered.

Nominal Size 

The nominal size and pressure rating of a piping system are foundational in determining the required thickness of a blind flange. Larger pipe sizes and higher pressure ratings demand thicker flanges to withstand the increased stress. Here’s a brief look at why these elements are crucial:

  • Nominal Pipe Size (NPS) directly influences the flange’s outer diameter and, in turn, its overall design. A larger diameter means more material is needed to ensure the flange can handle the imposed load without failing.
  • Pressure Rating (Class) defines the maximum pressure the flange is designed to handle at a specific temperature. This rating is typically denoted as Class 150, 300, 600, etc. The higher the class, the thicker the flange required to withstand the pressure without deforming or breaking.

Understanding these aspects helps in selecting the right blind flange that can handle the anticipated pressure while fitting perfectly with the rest of the piping system.

Material Strength and Temperature

Another critical factor influencing blind flange thickness is the combination of the material’s strength and the operational temperature. Different materials react differently under stress and temperature changes:

  • Material Grade and Type: Whether it’s carbon steel, stainless steel, or a more exotic alloy, each material has a distinct set of properties affecting its performance under pressure. High-strength materials can be thinner than those of lower strength because they can withstand more pressure.
  • Temperature: Flange materials expand under heat, which can affect their strength and, consequently, the thickness requirement. High operational temperatures necessitate thicker flanges to maintain integrity.

Choosing the correct material and accounting for temperature variations are paramount to ensuring the flange does not fail under operational conditions.

How to Calculate Blind Flange Thickness

Flange Pressure Rating

The pressure rating of a flange is paramount. This rating determines the maximum pressure the flange can withstand at a specific temperature. Higher pressure ratings usually mean that I’ll need a thicker flange to cope with the increased stress. It’s imperative to match the flange’s pressure rating with the system’s requirements to avoid any potential failures.

The American National Standards Institute (ANSI) provides guidelines on the pressure ratings for flanges, ensuring that I select the right thickness for the job. Here’s a quick look at how pressure ratings can influence flange thickness:

Pressure Class Typical Thickness Requirement 


Less Thick


Moderately Thick




Very Thick

Flange Material

The material of the flange significantly affects its required thickness. Different materials have varying strengths and limitations, influencing how thick the flange needs to be to withstand the operating conditions. For instance, carbon steel is a popular choice due to its strength and versatility, allowing for thinner flanges compared to materials with lower tensile strength.

On the other hand, materials like stainless steel, which resist corrosion better, might require different considerations for thickness based on the environment they’ll be used in. It’s crucial to consider both the mechanical properties and the chemical compatibility of the material when determining the optimal flange thickness.

Bolt Holes

The configuration and size of bolt holes on a flange also play a critical role in the calculation of its thickness. The bolt holes must be properly aligned and spaced to distribute the load evenly across the flange. Incorrectly sized or spaced bolt holes can lead to uneven stress distribution, potentially causing the flange to fail under pressure.

It’s essential to ensure that the diameter and spacing of bolt holes comply with industry standards, which are designed to maximize the effectiveness and safety of the flange connection. The number and size of bolts needed are directly related to the flange’s pressure class and size, requiring careful consideration in the overall design and calculation of flange thickness.

By keeping these factors in mind, I’m better equipped to calculate the appropriate thickness for blind flanges, ensuring the integrity and efficiency of the piping system.

How to Calculate Blind Flange Thickness

Calculation method for blind flange thickness

In the intricate world of piping design and maintenance, determining the correct thickness of a blind flange is crucial. Let’s dive deeper into the exact methods used, starting with the ASME B16.5 standard.

ASME B16.5 Formula

The American Society of Mechanical Engineers (ASME) B16.5 standard provides the formula necessary for calculating the minimum thickness of a blind flange. This formula considers various factors such as pressure, material strength, and dimensions to ensure safety and efficiency. The formula, although seemingly daunting at first glance, becomes manageable once broken down.

Example Calculation

Let’s run through an example calculation to illustrate the process. Suppose we’re working with a 24-inch nominal pipe size (NPS) blind flange, under a pressure class of 150, and using ASTM A105 carbon steel. Given these parameters, the formula from the ASME B16.5 standard is:

[ t = \frac{{PD}}{SE-0.6P} + C ]


  • ( t ) = minimum thickness of the flange (inches),
  • ( P ) = design pressure (psi),
  • ( D ) = outside diameter of flange (inches),
  • ( S ) = maximum allowable stress for material at design temperature (psi),
  • ( E ) = joint efficiency,
  • ( C ) = corrosion allowance (typically 0 if not specified).

For ASTM A105 carbon steel, the maximum allowable stress (( S )) is 20,000 psi, and we’ll assume a design pressure (( P )) of 285 psi, with an E value of 1 (for a seamless flange), and a corrosion allowance (C) of 0. The outside diameter (D) of a 24-inch NPS flange can be found in flange dimension tables, let’s use 32 inches as a common value for this example.

Plugging these numbers into the formula gives:

[ t = \frac{{285 \times 32}}{{20,000 – 0.6 \times 285}} + 0 ]

[ t = \frac{{9120}}{{20,000 – 171}} ]

[ t = \frac{{9120}}{{19829}} ]

[ t \approx 0.46 \text{ inches} ]

This calculation tells me that the minimum required thickness for my 24-inch NPS ASTM A105 carbon steel blind flange, under a pressure class of 150, is 0.46 inches. However, it’s crucial to remember that this is the minimum thickness. Practical considerations, such as manufacturing tolerances and potential corrosion over the flange’s lifespan, may necessitate a thicker flange.

Common errors to avoid when calculating blind flange thickness

When diving into the world of piping systems, accurately calculating blind flange thickness is pivotal. In my experience, there are certain pitfalls that, if you’re not careful, can significantly skew the accuracy of your calculations. Let’s walk through these common errors so you can steer clear of them.

How to Calculate Blind Flange Thickness

Incorrectly Applying Safety Factors

Explicit in the ASME B16.5 standard, safety factors are integral to ensuring the reliability and safety of a flange under operational conditions. However, a common error I’ve noticed is either completely overlooking these safety factors or misapplying them. Remember, safety factors account for unexpected operational stresses such as pressure spikes or mechanical impact.

The key is to correctly apply the standard’s recommended safety margins. This involves understanding the operational environment of your piping system. For stainless steel and carbon steel, the materials predominantly used in these contexts, safety factors might differ based on the corrosive nature of the fluid being transported or the temperature variances. Not adjusting safety factors appropriately for the specific scenario can lead to underestimating the needed thickness, compromising the flange’s integrity.

Neglecting Expansion and Contraction

Another oversight in calculating blind flange thickness is neglecting the material’s expansion and contraction. Metal pipes and flanges will expand when heated and contract when cooled. This dimensional change can cause significant stress on the flange, especially in systems experiencing wide temperature variations.

Accounting for thermal expansion involves not only the operational temperature but also considering the temperature during shutdowns and startups. For example, if a system operates at 350°F but may cool down to ambient temperature during shutdowns, the material of the flange needs to accommodate this range without losing its integrity or causing leaks.

Understanding the coefficient of thermal expansion for the chosen material is crucial. For instance, the coefficient for carbon steel is (12 \times 10^{-6} /°C), whereas for stainless steel, it’s approximately (16 \times 10^{-6} /°C). Using these coefficients in your calculations will help ensure that the flange maintains its seal integrity under temperature variances.

By paying close attention to these aspects, you’ll enhance the reliability and safety of your piping system. Always double-check your calculations and consider these factors to ensure that your blind flanges perform optimally under all operational conditions.


Mastering the art of calculating blind flange thickness is crucial for the safety and reliability of piping systems. I’ve shared insights on avoiding common errors and the significance of considering safety factors and material expansion.

Remember, precision in these calculations isn’t just about adhering to standards—it’s about ensuring the longevity and efficiency of your systems. With the right approach, you’ll not only safeguard your projects but also enhance their overall performance. Let’s apply these principles diligently for optimal results.

As a forging manufacturer with over 30 years of industry experience, we have sufficient experience to meet the diverse needs of our customers.

Moreover, we can produce cast and forged products that meet various requirements according to customer demands, such as various flanges, forging railway wheels, and so on. These will help customers better solve the difficulties encountered in production. Therefore, if you have any questions, please do not hesitate to contact us immediately.

Frequently Asked Questions

What is a blind flange?

A blind flange is a plate for covering or closing the end of a pipe. It is a crucial component in managing the flow of materials through pipe systems, allowing for easy access for inspection or modification.

How can you calculate the thickness of a blind flange?

The thickness of a blind flange can be calculated using the ASME B16.5 standard equation. This equation considers various factors including the pitch circle diameter, internal pressure, and allowable stress to determine the minimum required thickness.

What is the pitch circle diameter?

The pitch circle diameter (PCD) is the diameter of the circle that passes through the center of the flange’s bolt holes. It is an essential measurement for ensuring that the bolt holes align properly during installation.

Why is it important to round up the calculated thickness?

Rounding up the calculated thickness of a blind flange is important for safety and compliance. It ensures that the flange has a sufficient margin to handle pressure and stress without failing, adhering to safety standards and guidelines.

Should I always use the latest standards and materials data for calculations?

Yes, it is crucial to consult the latest standards and materials data when calculating the thickness of a blind flange. This ensures that your calculations are accurate, compliant, and based on the most current information available, considering any changes or updates to standards and material properties.