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Applications of High-Pressure Tube Unions

High Pressure Tube Unions

Whether you work at a power plant or in industrial manufacturing, you know how important it is to have failsafe equipment. High-pressure tube unions are required in a variety of sectors where you have to handle high pressures, extreme temperatures, aggressive media or hot vapors with high process reliability. . Learn more about tube fittings, benefits, and installation in this guide from DILO.

Table of Content

  • What Are Tube Unions?
  • Applications of Tube Unions
  • Things to Look for When Purchasing Tube Unions
  • DILO High-Pressure Tube Unions
  • Installation and Maintenance of Tube Unions
  • Advantages of Using Tube Unions
  • Connect with DILO Today

What Are Tube Unions?


A tube union is a type of metal compression fitting used in piping systems, used to control the flow of liquids or gas. As the name implies, high-pressure tube unions need to be able to withstand compressed  gas or fluids. Types of high-pressure tube unions include:


  • Straight unions
  • Angle Unions
  • Gauge connecting unions
  • Tee and L-unions
  • Superheated steam unions

Applications of Tube Unions


Tube fittings are needed in a wide range of sectors and industries that handle high-pressure gases or fluids. These applications include:


  • Aerospace industry
  • Chemical and petrochemical industry
  • Compressor engineering
  • Hydrogen applications
  • Metal and steel industry
  • Pipework systems and apparatus construction
  • Power plants
  • Turbine sector


Things to Look for When Purchasing Tube Unions

Any professional that works with industrial gas knows the importance of reliable, high-quality equipment. When sourcing tube unions, there are a few key factors to consider:



High-pressure tube fittings should be made from durable metals that are non-corrosive and meet minimum requirements for mechanical strength. When evaluating tube unions, look for products that meet the material specifications of American Iron and Steel Institute (AISI). DILO unions are available in:

  • 1.0460 (A): Non-alloy quality steel
  • 1.4571 (C): Weldable austenitic stainless steel 
  • 1.7335 (D): Alloy steel
  • 1.4922 (Q): High strength chromium stainless steel 

Pressure Rating


Tube unions must be able to withstand high pressures, especially in hydrogen gas applications. However, the required pressure rating will depend on the application. For example, DILO manufactures a line of tube unions for pressure ranges from 100 – 320 bar, as well as tube unions for pressures from 640 – 1000 bar.

Size and Compatibility


Measurements of pipes and fittings are often given in inches as Nominal Pipe Size (NPS) or in millimeters as Diametre Normal (DN). To avoid malfunction or leaks, the tube union diameter and the pipe diameter must match. At DILO, we provide a variety of unions available for tube diameters ranging from DN 3 to DN 50.

Leak Tested


Because industrial gas emissions can be harmful to the environment, leak resistance is one of the most important criteria to consider. High pressure, extreme temperatures, and vibrations can all test the quality of a seal. A tongue and groove design can guarantee a strong seal without an intermediate tightening compound.

Standards and Certification


Look for tube fittings from manufacturers who have met International Organization for Standardization (ISO) requirements, such as ISO 9001:2015, which sets the standards for quality management systems. Tube union suppliers should also hold TÜV Product Certification, a globally recognized standard for product safety testing and regulatory compliance. 

DILO High-Pressure Tube Unions

The DILO seal principle sets our tube unions apart from the competition. DILO’s fittings are made with a tongue and groove seal with little depth of immersion. Direct contact between the tongue and groove parts creates a high-stability seal that resists high temperatures, as well as vibration in the tube.

DILO’s tube fittings are easy to assemble and can be loosened and reconnected whenever needed. Each type of tube union we offer meets rigorous quality standards:

  • Leak rate less than or equal to 1x10-8 mbar l/s
  • Suitable for pressures up to 1,000 bar
  • Temperature resistant from -270 °C up to +650 °C 
  • Applicable for all fluids with the correct steel grade
  • Long-term, high level of gas tightness
  • Simple assembly and disassembly
  • Resistant to vibrations without additional protection
  • Complete interchangeability among pieces of the same type


A complete list of DILO tube unions and specifications is available in our Product Catalog

Installation and Maintenance of Tube Unions

DILO tube unions are simple to install and don’t require any special assembly steps. Follow these guidelines when installing a tube fitting:

Preparing the Pipe


Once you have determined the exact pipe lengths needed, saw the tube off squarely at the appropriate point. Deburr the bores to create a smooth surface and chamfer the tube edges in compliance with DIN EN ISO 9692-1.

Installing the Union 


The assembled tube union can be tack-welded to the tube with the clamping nut tightened slightly. Once tack welding is complete, uncouple the union and weld the tube connections. Reconnect the tube union and remove any residue. Ensure the tongue and groove are clear of any impurities. The threads of the tube union and the clamping nut surface should be slightly oiled with an appropriate lubricant.



DILO’s high-pressure tube fittings do not require maintenance and can be disconnected and reconnected as many times as you wish. However, when transporting welded tubes, the sealing areas should be protected with plastic caps to avoid any mechanical damage. 

Advantages of Using Tube Unions

High-pressure tube unions offer many benefits in industrial applications, such as:

  • Durability: Even after being loosened and reconnected multiple times, DILO’s fittings provide the same high level of gas tightness, regardless of static or dynamic stress. 
  • Ease: Our high-pressure tube unions are easy to install and do not need regular maintenance.
  • Versatility: DILO fittings of the same type are completely interchangeable. Plus, our fittings are well-suited for hydrogen application, as well as sulfur hexafluoride (SF6).
  • Custom solutions: If you have a unique application, DILO is flexible and can work with you to find a solution. 

Connect with DILO Today

[Insert quote from CR about the future of DILO valves & coupling market opportunities] For over 70 years DILO has produced fittings and couplings.  The DILO seal has been trusted by a wide range of users as the standard for leak-proof connections in many applications.  We look forward to finding new uses and providing solutions for emission-free gas and fluid handling, with the “backbone” of DILO’s product portfolio - our High Pressure Tube Union Catalog. 

At DILO, we’re dedicated to providing high-quality fittings, monitoring equipment, and other GIE products. With over 50 years of experience working with SF6 and alternative gases, DILO partners with utility companies, energy cooperatives, private corporations, and government agencies. We demonstrate our commitment to a zero emissions philosophy through rigorous product testing and standards, as well as our IACET-accredited safety and handling training programs. For more information about our high-pressure tube unions, other products, and gas handling services, contact us today.

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