Furick Accessories FAQs
Answers to common questions about TIG trailing shields, purge systems, torch cable covers and torch holders.
Which metals need a trailing shield?
Trailing shields are mainly used on metals that react with air while hot, such as titanium, zirconium and cobalt alloys. They are also used on stainless and duplex steels, nickel alloys and some other alloy steels where a bright, oxide-free surface or good corrosion resistance is wanted.
Ordinary carbon steel in normal fabrication usually does not need one. Whether you need a trailing shield depends on the material, the specification you weld to and how much oxidation is acceptable, so check the procedure for your job.
Should I choose a flat or a curved trailing shield?
The shape needs to follow the surface you are welding. Flat shields suit sheet and plate, and curved shields are made to match the diameter of pipe, tube or a vessel. Internal-radius versions exist for welding inside pipes and vessels.
A shield that does not sit close to the work lets air in at the sides, so choose the one that matches your joint and size. Check the shield fits the nozzle on your torch and that the length suits your travel speed and the heat of the weld, as longer shields are used when more cooling cover is needed.
If I use a trailing shield, do I still need a back purge?
Often yes. A trailing shield protects the face of the weld, but the root side of a full-penetration weld on stainless steel is exposed to air unless it is purged. An effective back purge minimises heat tint, and the oxygen in the purge space should be controlled and kept low before welding starts.
Heat tint reduces corrosion resistance and has to be cleaned off if it forms. Whether a back purge is needed depends on the material, the joint and your welding specification, so follow your procedure and the maker's instructions.
How do I know my purge is clean enough before I weld?
Do not rely on guesswork or on timing alone. The oxygen content in the purge space should be controlled and checked before welding starts, and a purpose-made oxygen monitor reading from the purge space is the usual way to do this.
The oxygen level you need depends on the material and the specification, and the time to purge depends on the pipe size, volume and flow rate. Do not set the flow so high that pressure builds up in the pipe, as this can distort the root bead. Follow your procedure and the maker's instructions for the purge equipment.