How to Tighten Flange Bolts

In the construction in the installation of pipelines for industrial use, machines or pressure vessels, connections made with flanges work like a strong handshake between the components – secure and coordinated. The force of the handshake relies on a single player – the bolt that holds the flange.

These seemingly insignificant bolts are actually the unnoticed heroes that are responsible for the system’s safety and sealing integrity. If they are not tightened correctly, they can cause small leaks to massive malfunctions in the equipment, costly downtime, and even major accidents. In this post we’ll guide you on the proper way to tighten Flange bolts to ensure a smooth, no leaks, and steer away from costly issues.

Part 1. What is a Flange Bolt?

A flange bolt is a form of fastener designed specifically to join two flanges to each other, usually using gasket. Through applying axial clamping force by tightening the flange bolt compresses the flanges, resulting in a solid seal and solid mechanical connection.

Flange bolts play a crucial function in industrial systems. They are extensively utilized in pressure vessels and pipelines across a range of sectors, such as petroleum, chemical processing natural gas energy generation and water processing marine engineering and pharmaceuticals.

Flange bolts come in many kinds to meet different needs and conditions for installation:

Bolts with threaded holes The bolts feature threads across every inch of the shaft making it possible an adjustable length of tightening and are ideal for all-purpose connections.

Bolts with threads that are partially threaded The bolts are threaded partially. threads that only cover a small portion of the shaft. They are typically used in applications that require greater shear strength.

Strong bolts made from high-tensile material These bolts provide superior durability and tensile strength as well as corrosion resistance suitable for high pressure or high temperature environments.

Flange bolts are able to be adapted in accordance with industrial standards (such such as ANSI, DIN, GB and more. ) Materials (carbon steel, stainless steel and alloy steel) as well as coatings (zinc-plated Dacromet hot-dip galvanized,) and even strength grade (such such as grades like 8.8, 10.9, or 12.9) to fulfill the specific sealing as well as safety and endurance demands of a project. A proper selection and fitting of flange bolts is crucial to ensure the security of the piping system as well as stopping leaks, damage or even accidents.

Part 2. Why Must Flange Bolts Be Properly Tightened?

The correct tightening of flange bolts crucial to ensure security as well as the stability of any pipe or system. Here’s why:

Prevent Medium Leakage

If the flange bolts are loose or not properly tightened the gasket that connects the flanges could not be compressed evenly. This uneven force distribution could cause gaps that can lead to leakage of the medium being transported, whether it’s liquid, gas, or steam. This poses significant environmental and safety hazards especially in high pressure or hazardous systems.

Ensure Stable Equipment Operation

The incorrect torque of bolts could cause flange surfaces to swell or get misaligned. This can cause excessive stress or vibrations in the equipment and pipelines connected to it which could disrupt normal operation and causing premature wear and failure.

Guard Bolts from damage

Insufficient tightening of the bolt could stretch it over its yield strength and cause permanent deformation, or even breaking under operating load. However when tightening too much, it creates an insufficient preload, making the bolt difficult to keep a good seal and increasing the possibility of loosening as a result of vibration or thermal cycling. Finding the appropriate balance is essential to ensuring durability and high performance.

Part 3. How to Tighten Flange Bolts Step by Step

Step 1. Preparations Before Tightening Flange Bolts

Before you begin the process of tightening It is recommended to prepare the necessary tools as well as supplies prepared:

Torque wrench (to ensure precise torque application)
Anti-seize or Lubricant (e.g. copper grease)
Safety equipment that is worn by the individual (such as safety goggles and gloves)
Bol and Flange specifications as well as a torque reference chart
Also, be sure you check these:
The flange’s surface is clean and free of dust, dirt or scratches.
The gasket is correctly placed and is unharmed.
All bolts meet the exact specifications and free of defects.

Step 2: Hand-Tighten All Bolts

Start by inserting and tightening all bolts equally around the flange. This is the first step that allows the flanges’ faces to be joined naturally, without using excessive torque. In this phase, it is important to make sure that all parts are aligned and seated correctly.

Step 3 : Tighten in a Criss-Cross Pattern, in Stages

To prevent uneven pressure which could cause warping of the flange, or even damage the gasket need to be tightened in an alternating (criss-cross) order. This will ensure even distribution of the clamping force over the entire flange’s surface.

It is recommended to tighten bolts over three stages in increments:

Round 1: tighten every bolt until 30% of targeted torque.
Second Round: Increase the torque to 60% desired torque
Third Round: tighten the bolt to 100% of final torque

If required, you can perform an additional round of final torque test to make sure that all bolts are evenly and properly torqued.

Step 4 : Final Inspection and Documentation

Make use of the torque wrench for the complete inspection making sure that each bolt is in the same pattern of criss-cross.
Record the torque values of each bolt in your installation or maintenance record.
Check the gasket’s visual appearance to ensure that it is compressed evenly and ensure that the flanges are free of any distortion.

By following these steps cautiously by following these steps, you will significantly lower the possibility of leaks, damage to the flange or bolt failure, creating the foundation to ensure a safe and secure system.

Part 4. Common Tighten Flange Bolt Mistakes and How to Avoid

Here, we’ll go over the most common errors made in the process and provide advice regarding how you can avoid these for the best outcomes.

Incorrect Tightening Sequence

Effect: Uneven pressure on the gasket, resulting in leakage.
What to avoid: Always follow the diagonal pattern of crisscross tightening to ensure a uniform distribution of the clamping force.

Failure to Use Lubricant

Consequences: Inaccurate torque application that results in the bolt to become bound or loose.
What to avoid:Apply the appropriate lubricant or anti-seize compound on the threads of bolts to ensure a perfect tightening and precise torque.

Manual Torque Estimation

Consequences:Poor precision, making it simple to over- or undertighten bolts.
What to avoid:Use a calibrated torque wrench to ensure precise and regular torque application for each bolt.

Over-tightening or Under-tightening

Consequences:Flange distortion or bolts becoming looser over time.
What to avoid: Tighten bolts in several rounds and stages gradually increasing the torque until you reach the target you have set. Always make sure you are using the appropriate torque during the final round to avoid over-tightening and under-tightening.

KENENG, Your Trusted Flange Bolt Manufacturing Partner

Correctly tightening flange bolts important for the stability of your equipment but is also a crucial factor in making sure that personnel are safe. If you follow the correct procedures and using the appropriate equipment, and adhering to established operating procedures and procedures, you can lower the risk of leakage and increase the life the equipment.

KENENG specialises in research design, development and production of top-quality Flange bolts. The products are in compliance with numerous international standards, such as ASME, DIN, and GB. It includes:

Diverse types of (Carbon Steel, Stainless Steel, Alloy Steel)

Multiple sizes (M5~M20)

The treatment of the surface (Hot-dip Galvanized Electroplated and Black Oxide and more.)

Assistance for production in bulk as well as specific needs

If you require bolts to flange your engineering project, or for replacement or maintenance, KENENG can provide you with reliable and safe solutions. Do not hesitate to contact KENENG to learn more!