Tips for connecting concentric reducers and flanges

Keywords: concentric reducers and flanges connection, pipe reducers and flanges connecting, pipe reducers
Can concentric reducers and flanges be directly connected?
Connecting concentric reducers and pipe flanges is a common operation in pipeline systems, and it is necessary to ensure sealing, centering and structural stability. Concentric reducers and pipe flanges can be directly connected through flange connectors, but it is necessary to pay attention to selecting the appropriate flange type and connection method to ensure the quality and safety of the connection.

Tips for connecting concentric reducers and flanges:

In engineering practice, connecting concentric reducers and pipe flanges is a common task. Understanding the connection methods and precautions between them is crucial to ensuring the quality and safety of the project. The following are key tips and steps:


 concentric reducers and flanges connection


1) Preparation

Before connecting concentric reducers and flanges, the following preparations need to be made:

1. Check whether the model, material, pressure level and specification of the concentric reducer and flange meet the design requirements to ensure that the connection between the two matches. The flange sealing surface type (raised face RF, flat face FF, etc.) is consistent with the pipeline requirements.
2. Check whether the surface of the concentric reducer and flange has defects such as rust and cracks. If necessary, deal with them in time.
3. Prepare the required connectors, such as bolts, nuts, gaskets, etc., and check whether their quality meets the requirements.
4. Prepare the required tools: bolt tensioner, torque wrench, level, centering rod, flange sealing gasket (such as metal spiral wound gasket, graphite gasket), etc.

2) Connection process of concentric reducer and flange

The connection between concentric reducer and flange is mainly achieved through flange connectors. The specific steps are as follows:

1. Align the connection ports of the concentric reducer and flange to ensure that the connection surface is flat and free of impurities.

Centering adjustment:
Temporarily spot weld the reducer and flange or fix them with flange clamps, use a level to check the parallelism of the flanges at both ends, and ensure that the concentricity deviation is ≤1mm. The center lines of the large end and the small end of the reducer must be strictly coincident.

Welding requirements (if welded):
Use symmetrical segmented welding to reduce thermal deformation. First spot weld to position, then full weld. Stainless steel needs to be welded with argon arc welding (TIG) and protected by argon.

2. Place a gasket at the connection port. The function of the gasket is to increase the sealing and prevent leakage.

Gasket selection:
Choose the gasket material according to the medium (high temperature, corrosive, etc.). The size must match the flange sealing surface and must not block the bolt hole.

Sealing gasket installation tips:
The gasket is placed in the center. A small amount of lubricant (such as molybdenum disulfide) can be applied to avoid displacement. It is forbidden to reuse old gaskets.

3. Use bolts and nuts to tightly fix the concentric reducer and flange together. During the tightening process, pay attention to uniform force to avoid deformation or damage caused by excessive tightening.

Bolt pre-tightening sequence:
Tighten in 3 steps according to the "cross symmetry method":
① Pre-tighten 30% torque → ② 70% torque → ③ 100% torque
Use a torque wrench to ensure uniform torque (reference standards such as ASME B16.5).

Anti-loosening measures:
Under high temperature conditions, apply high temperature anti-seizure agent to bolts and add disc spring gaskets to nuts.

3) Inspection after connecting concentric reducers and flanges

After the connection is completed, the following inspections need to be carried out to ensure the quality and safety of the connection:

1. Check whether the connection is tight and seamless. If necessary, readjust and tighten.
2. Check whether the connectors are complete and intact. If they are missing or damaged, they need to be replaced in time.

3. Test the sealing of the connection to ensure that there is no leakage.


Leak test:
Check the sealing surface with soapy water or helium detector. The water pressure test pressure is 1.5 times the design pressure.

Stress investigation:
Check whether the pipeline support is reasonable to avoid the reducer from being subjected to additional bending moment or vibration.

4) Precautions

During the connection process of concentric reducers and flanges, the following points need to be noted:

1. Select the appropriate flange type and connector according to the project requirements and pipeline materials. 

2. Keep the pipes and flanges clean during the connection process to avoid impurities affecting the connection quality.

3. Strictly follow the specifications to ensure the safety and quality of the connection process.
4. For high-pressure or highly toxic medium pipelines, it is recommended to use a pre-tightening hydraulic tensioner and record the bolt elongation to ensure accuracy. The operation must comply with ASME B31.3 or GB 50235 specifications.

5) Common Problems

Flange deflection: fine-tune with a wedge-shaped gasket, but ensure that the gasket does not protrude from the sealing surface.
Bolt breakage: When replacing, loosen the entire bolt and tighten it again in sequence to avoid local stress concentration.
Reducer vibration: add a pipe clamp or shock absorber to check whether the fluid pulsation is too large.

In short, the connection of concentric reducers and flanges is an important engineering task that needs to be taken seriously. By understanding the connection method, precautions and inspection requirements, the quality and safety of the connection can be ensured, providing guarantees for the smooth progress of the project.


Read more: Pipe and flange connection or Pipe reducer size selection

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