Weld purging techniques
Equipment has been developed over the past decade to make
purging much easier. Currently available systems are robust
and suitable for multi-use applications. They can be supplied
to cover the size range between 25 - 2400 mm dia.
The most effective devices are those based on
connected inflatable dams. These are 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 with
oil and gas pipelines and processing plants where the
elimination of contamination is essential.
Purge gas oxygen content can be controlled by using an
oxygen monitor. These instruments not only measure oxygen
levels, but will inhibit welding if the level is above that set by
the operator. Recording and analysing software consequently
provides information for quality control purposes.
Conclusion
Even very low oxygen concentrations in weld gases can give
rise to discolouration and corrosion. Controlling oxygen level
in purge gas can be effected simply and efficiently using
contemporary integrated purge systems.
References
1.
EASTWOOD et al. 1993, welding stainless steel to meet hygienic requirements,
document 9, European Hygienic Engineering Design Group (EHEDG).
2.
TITZ, Jörg-Thomas, ‘Microbiologically influenced corrosion of stainless steel’, 2
nd
symposium on orbital welding in high purity industries, La Baule, France.
3.
‘Effects of purge gas purity and Chelan passivation on the corrosion resistance
of orbitally welded 316L stainless steel tubing’,
Pharmaceutical Engineering
, Vol
17, No 1 & 2, 1997.
4.
‘Considerations for Orbital Welding of Corrosion Resistant Materials to the
ASME Bioprocessing Equipment Standard’, Dr B. K. Henon, Arc Machines, Inc.,
Stainless Steel America Conference, 2008.
5.
AMMANN, Thomas, ‘Purging while welding’, BOC Australia, document 2010.
6.
NETTEN, G., ‘Necessity of removal of heat tints on stainless steel to avoid or
minimise corrosion’,
Vecon Netherlands Technical Bulletin
, July 2005.
7.
TABAN et al., ‘Effect of the purging gas on properties of 304H GTA welds’,
Welding Journal
, April 2014, Vol 93.
Figure 4.
Weld Purging Monitor
®
that can read from
atmospheric oxygen levels down to 10 ppm.
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