Welding Stainless Steel

Avoiding loss of corrosion

Many industries rely on the corrosion resistance of stainless steels including the food, beverage, pharmaceutical, semiconductor, petrochemical and nuclear.

It has become common practice in some applications to accept discolouration and remove it post-welding, but this can be very expensive. It is time-consuming and, where access is limited, difficult to achieve with any degree of success. Some methods require specialist equipment.

The expense of post-weld operations is often overlooked and not considered part of the welding process. They are largely applied manually and thus prone to significant variations in effectiveness. They are seen as an easy option but can easily exceed the welding costs.

welding stainless steel

The most effective method of preventing discolouration is to use a weld purging technique. Purging involves eliminating oxygen from the heated weld zones by displacing the air with an inert gas, usually argon.

Available Weld Purging methods

Inflatable Systems are the only totally reliable and are the most effective tube and pipe purging systems. 

welding stainless steel

Considerable design effort has been applied to these inflatable solutions over the past decade or so and currently available systems address the problems of controlled inert gas pressure and flow, the need for easy and rapid deployment and removal to limit overall welding time. 

PurgElite® Systems • First ever 1” (25 mm) system size available

  • Range from 1 – 24” (25 – 610 mm)
  • Special gas saving designs
  • Flexible spinal hose with heat protection
  • Heat Cover and PurgeGate® available as accessories

QuickPurge® Systems

  • Central Sleeve with RootGlo®
  • IntaCal® purge gas release system
  • Reduces purge volume
  • Sizes from 6 to 88” (152 – 2,235 mm)

HotPurge® Systems

  • Heat resistant. Withstands 300ºC (572ºF) for up to 24 hours
  • Suitable for pre-heated pipework
  • Ideal for P91 and other chrome pipework in power stations and refineries
  • With RootGlo®, IntaCal® and PurgeGate®

Monitoring of oxygen content in the purge gas

The fact that even very small amounts of oxygen in the purge gas can cause discolouration around the weld underbead makes it desirable that specialised instruments be used to measure residual oxygen. Recommended practice to ensure acceptable discolouration is to maintain an oxygen level below 50 ppm (0.005%) for stainless steel.

Two essential characteristics of a suitable instrument are that it must have an adequate measuring range and it must sample the purge gas inside the purge volume. The sensitivity should be such that an oxygen level as low as 10 ppm can be detected. Instruments that only display down to 1000 ppm (0.1%) are totally unsuitable.

welding stainless steel

Weld Purge Monitor® Range:

PurgEye® 100 IP65, low cost, dustproof and waterproof hand held unit for reading down to 100 ppm.

PurgEye® 200 with PurgeNet™ is our hand held, rechargeable battery driven Weld Purge Monitor® for reading very accurately down to 10 ppm complete with electromechanical sampling pump.

PurgEye® 300 Nano, the worlds first and only super low cost, entry level, mains power driven Weld Purge Monitor® measuring accurately down to 10 ppm.

PurgEye® 500 Desk with PurgeNet™ uses an internal electromechanical pump to draw the gas across the sensor. It also has the switching capabilities and the PurgeLog™ Software.

PurgEye® 600 a computerised, touch screen model measuring very accurately from atmospheric level down to 10 ppm, with high and low oxygen level switching capabilities, data capture via USB using PurgeLog™ software for recording purging results for subsequent evaluation and provision of a quality control document.

PurgEye® 1000 monitor with PurgeNet™ has been developed for those instances where the measuring point is more than 20 metres away from the monitor. The slow time for the gas to travel and reach the sensor and the contamination of actual reading that can take place inside the gas tube, leads to serious delays and erratic readings.

PurgEye® 1500 Site with PurgeNet™, designed and manufactured in a robust, virtually non-destructible case, perfect for dusty, hazardous, on-site conditions, measuring oxygen levels from 1,000 ppm down to 10 ppm. IP68 rated with the lid closed.

What is PurgeNet™? 

PurgeNet™ controls the welding power sources such as orbital welders and any other automatic welding systems to switch on and off according to oxygen levels. PurgeNet™ can be used with PurgeLog™ software to transfer weld purge data for quality control of welds. PurgeNet™ connects to other smart accessories for weld purging, including the Traffic Light System, which gives a visual warning during welding in case of rising of falling oxygen levels.

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