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DIN EN ISO 5817 and Welding Quality of Stationary Mixers

August 31, 2025
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In industrial production, welding is one of the most important processes in the manufacture of pressure equipment and sensitive devices. In equipment such as  stationary  mixers used in the chemical, oil and gas, food, and water treatment industries, the quality of the weld directly affects not only its performance, but also its safety and lifespan. The DIN   EN ISO 5817
standardIt is one of the most important international references for determining welding quality levels, as it provides accurate criteria for its evaluation and acceptance. In this article, we will analyze this standard and its importance for its application in the manufacture of stationary mixers.

What is DIN EN ISO 5817?

DIN EN ISO 5817  , whose full  name is “Welding – Fusion Welded Joints in Steel, Nickel, Titanium and their Alloys (Except Gerder Welding) – Quality Grades for Defects”, specifies  the quality grades of fusion  welded joints in steel, nickel, titanium and their alloys (except for beam welding)  .

The standard defines three levels of quality:

  • B. (Strict):  Highest quality for sensitive applications.

  • C (Medium):  Suitable for most industrial applications.

  • D (Low):  Suitable for applications with low functional sensitivity and safety.

The choice of quality grade depends on factors such as operating pressure, temperature, type of liquid, and safety requirements.

The Relationship Between Welding Quality and Static Mixer Performance

In a stationary mixer, the mixing elements within the pipes are connected to the main body by the seams. These seams must be:

  1. It has  enough mechanical strength to withstand pressure and vibration.

  2. It provides  high chemical resistance to prevent corrosion when in contact with liquids.

  3. Creating  smooth interior surfaces to prevent particle buildup and contamination.

Poor welding quality will lead to cracks, pores, incomplete penetration, deformation, and other problems, which directly affect the mixing efficiency and the life of the equipment.

of Non-Continuity and Acceptance Criteria in DIN EN ISO 5817

This specification specifies the types of welding defects and specifies the maximum allowable values for each quality level. The most important of these defects are:

1. Porosity

Bubbles left in the solder will reduce the mechanical force.

  • Class B: Very limited, small diameter, small quantity.

  • Grade C: Medium quantity and size.

  • Grade D: Higher porosity is allowed.

2. Incisions

presence of cracks is generally considered unacceptable at all levels of quality.

3. Incomplete penetration

When the filler or molten metal does not fully penetrate the thickness of the joint.

  • In Category B, this is practically unheard of.

  • It  is accepted at levels C and D, but with some restrictions.

4. Cut Down the Welding Edge

Depression at the edge of the weld can lead to stress concentrations.

5. Overlay

When the welded metal spreads into the parent material without bonding properly.

The welding quality control process during the manufacturing of stationary  mixers complies with the DIN EN ISO 5817 standard.

1. Choose the Right Quality Level

For stationary mixers for pressurized or corrosive liquids,  Class B or Class C are usually chosen.

2. Prepare the material and edges.

  • Choose a suitable alloy, such as 316L stainless steel for its high corrosion resistance.

  • Surface preparation by mechanical and chemical cleaning.

3. Choosing the welding method

  • For stainless steels,  TIG (GTAW) or MIG (GMAW) is usually used .      

  • In sensitive cases, multi-stage welding with precise temperature control is recommended.

4. Inspection during welding

  • Control the wire feeding speed and temperature.

  • Check the shape and size of the soldering tub.

  • Protection gas quality control.

5. Post-weld tests

  • A vision check (VT)  checks the appearance.

  • Permeable fluid (PT)  is used to detect surface cracks.

  • Examination of internal  defects using X-ray (RT)  or  ultrasound (UT).

Benefits of applying the DIN EN ISO 5817 standard in the production of stationary mixers

  1. Improving weld safety according to this standard
    reduces the risk of failure or sudden leakage.

  2. Improve the quality of flow and mixing.
    The smooth, weld-free inner surface reduces pressure drop and improves the mixing process.

  3. Reduced repair costs.
    High-quality welding reduces the number of repairs.

  4. Improving the credibility of the manufacturer by adhering to internationally recognized
    standards will allow it to gain the trust of domestic and international customers.

Challenges of Applying Industrial Standards

  • High-quality  non-destructive testing is expensive.

  • The precision  welding process requires specialized and trained personnel.

  • The raw material requirements are  more stringent, which will prolong the supply time.

Practical Tips from Stationary Mixer Manufacturers

  1. Implement the ISO 9001  quality management system to document processes.

  2. Continuous training of welders  in accordance with DIN EN ISO 5817 standard.

  3. Adopt advanced  welding equipment and automatic parameter control   . 

  4. Multi-stage  inspection from raw materials to finished products.

Conclusion

The DIN   EN ISO 5817  standard is a key reference standard for ensuring weld quality, and plays a pivotal role in the manufacture of sensitive equipment, such as stationary mixers. Stationary mixers that meet this standard  combine mechanical strength  with efficient hydraulic performance.
The application of this standard not only extends the life of the equipment and reduces its maintenance costs, but also enhances the credibility of the manufacturer in the domestic and international markets.