TPT March 2020

AR T I C L E

Huntingdon Fusion Techniques Limited

Purge gas oxygen content can be controlled by using an oxygen monitor. These instruments not only measure oxygen levels but can inhibit welding if the level is above that set by the operator. Recording and analysing software provides information for quality control purposes.

Few manufacturers are able to supply weld purging systems that can be used at the high temperatures prevailing during pre- and post-heating but some commercially available systems have been designed specifically to meet the requirements (see figure 1) However, it is clear that many companies still employ paper, cardboard and polystyrene foam as dam materials. These are prone to outgassing during use, they are difficult to insert and remove and may even ignite at the prevailing temperatures.

Figure 3: Oxygen monitor designed specifically for use in a welding environment. The PurgEye ® 7 range is capable of measuring residual oxygen content down to 10ppm

Figure 1: Hotpurge ® 7 systems cover the diameter range from 150 to 2,440mm. These systems are capable of withstanding temperatures up to 300°C for 24 hours). The inflatable seals are manufactured from flexible, thermally resistant engineering polymers

Conclusion Even very low oxygen concentrations in weld gases can give rise to discolouration, loss of corrosion resistance and reduction in mechanical strength. Controlling oxygen level in purge gas can be effected simply and efficiently using contemporary integrated purge systems.

Weld purging techniques The most effective devices are those based on connected inflatable dams. The inert gas input can be programmed to control gas flow and pressure during inflation and purging and once placed in position require little more input from an operator. The dams are fabricated using advanced engineering polymers and are thus suitable for use where elimination of contamination is essential.

References

1) World Nuclear Power Reactors & Uranium Requirements, World Nuclear Association, November 2016. 2) Analysis of Globally Installed Coal Fired Power Plant, Finkenrath et al, International Energy Agency, 2012. 3) BS EN ISO 13916:1997: ‘Welding: Guidance on the measurement of preheating temperature, British Standards Institution, 1997. 4) BS EN 1011-2: 2001: ‘Welding: Recommendations for welding of metallic materials. Arc welding of ferritic steels’, British Standards Institution, 2001. 5) The Welding Institute. Technical-knowledge series. 6) Bailey, N. Weldability of Ferritic Steels. The Welding Institute, 1995.

Huntingdon Fusion Techniques Limited 
– UK Fax: +44 1 554 836 837

Figure 2: Example of the PurgElite ® 7 range of fully integrated systems covering the 25 to 250mm pipe range. Complementary systems are available covering the diameter range between 150 and 2,440mm

Email: hft@huntingdonfusion.com Website: www.huntingdonfusion.com

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MARCH 2020