Automated GTAW Water Tank Manufacture and Gas Wastage
TVC was approached by a manufacturer of Duplex water tanks that back purge the tanks with forming gas. In their automated GTAW process, a tank is set up for purging while a pre-purged tank is welded.
Prior to purchasing TVC Oxygen monitoring and flow control equipment, an initial purge was carried out by maintaining a high flow rate for a set period of time. This method, however, has the disadvantage of often exceeding the nominal time to fully purge the vessel. This usually resulted in a large volume of gas wastage.
3-Stage Flow Control Solution
TVC’s solution was to supply a GPM Oxygen monitor with 3-stage flow control. The revised purge procedure using TVC’s equipment starts with the operator setting up the tank to be purged. The gas supply is connected and routed through the GPM 3-stage flow control box. The GPM sampling tube is connected to the tank and, once the ‘Start’ button is pressed, the GPM will begin sampling the O2 level. The flow control box starts the purge gas flowing at the high flow rate, in this case about 80 LPM.
Pre-programmed Alarm Levels
The GPM features two pre-programmed alarm levels. These alarms control the Oxygen levels at which the flow rates will change. In this solution, the high alarm level is set at 1000 PPM O2 and the low alarm at 50 PPM. When the O2 level drops below the high alarm level, the flow control automatically changes over from the high flow level of 80 LPM to the mid-flow level of 15 LPM. As the O2 level continues to drop, once the low-level alarm threshold is reached, the flow control changes to the lowest set flow rate of 5 LPM. The lowest flow rate is enough to maintain the purge until the operator is ready to transfer the purged tank onto the automated welding lathe.
Cost-saving Analysis
For every minute of high flow purge time saved, the client estimates saving £0.36 based on current forming gas costs. Although this may not seem a substantial cost saving, over the course of a 48-week year (5-day working week, 8-hour working day), saving 10 minutes every hour would result in a cost saving of £6,912.00.
The savings detailed above are for a single welding station, so the annual savings could be substantial for a large factory with multiple production lines. Given that TVC equipment costs would be recouped within 21 weeks, this is especially true.
To see if TVC can assist you with your purging, contact us to discuss your requirements.