super duplex

As part of our top tips series, we will be undertaking a Q&A with Paul Flynn – an experienced Supervisor at John Tracey Specialist Welding, each month, focusing on the range of exotic metals the team work with. This week, it is super duplex.

1. Three top tips when welding super duplex are:

  • When welding Super Duplex as with any stainless, your main focus should be on purging and this is the norm for high quality full penetration butt welds. You should always follow procedure for gas flow rates, as the correct flow rates and ppm of oxygen inside the purge area can massively affect your weld.
  • Super Duplex is a much tougher material to weld than 316l stainless and as such I have found using a different technique helps achieve high quality roots every time. I never add filler wire to the centre of the weld pool but instead I apply it to both side walls directly and wash arc through middle of pool.
  • Again, we must always keep Super Duplex segregated, across the area of work, tools, and consumables. Even although super duplex has excellent resistance to pitting, carbon particles can still easily contaminate the surface.

2.What equipment is required?

  • Air/water cooled TIG inverter, oxygen meter, bungs and dams, purge hoses/tape, digital thermometer, project specific tools and consumables.

3. What preparation is key?

  • Whilst there are a number of preparations to carry out before welding Super Duplex, I would pay special attention to purging. As with carbon inclusion, there are excellent ways and means of removing these contaminants but if your purge is wrong when you begin welding then it is already too late.                                       

4. Key challenges and how to overcome them:

  • When welding full penetration Super Duplex pipe butts it is very common for the butt to shrink and close in causing great problems rooting. This can easily be countered with the use of the correct amount of bullets/inserts to hold the welded joint firm. There is a delicate balance regarding heat when welding Super Duplex; you should be looking to keep an inter pass temperature between 125-150 to prevent unwanted intermetallic phases.

5. Safety considerations

  • As with all welding, respiratory health problems are a major issue and as such extraction, ventilation, air-fed systems and a general awareness and respect for the dangers welding as a whole can pose.