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Thermocouple and pin capacitor discharge welding

Thermocouple and pin capacitor discharge welding

Thermocouple and pin capacitor discharge welding

Almost all codes give the maximum of 125 watt seconds (Joules) for attaching thermocouples and insulation pins to code parts using capacitor discharge welding.
How was this limit reached? is it perhaps a carry-over from the withdrawal arc welding that was used prior to the introduction of CDW?
We find that for welding 12 gauge pins 125 watt seconds often does not give an acceptable weld. This leaves more arc marks than using a higher watt second setting.
Is there an acceptable way to increase this requirement?


RE: Thermocouple and pin capacitor discharge welding

First, the 125 watt-sec power limit was established based on initial long arc stud welding followed by CDW by two of the large boiler OEM's. The concern is to limit the size of the heat affected zone in the pressure retaining item wall thickness.

With that said, if you have actual test data that you would be willing to share, this could be presented to BPV I and a revision can be made. However, if you are unwilling to share your test data or the data is proprietary, there is no chance for revision.

RE: Thermocouple and pin capacitor discharge welding

There are other limitations depending on which ASME code you read, but keep in mind that the 125 watt-sec applies to non-subsequent Post Weld Heat Treatment.

If your parts receive subsequent PWHT, you can increase the 125 watt-sec to whatever fits your need.

RE: Thermocouple and pin capacitor discharge welding

ASME B31.3 only requires the 125 watt second if noted materials (P1 thru P5A & P15E) are not PWHT or preheated above 10 degrees celcius.

RE: Thermocouple and pin capacitor discharge welding

Thanks to all for the information: If my company was to request a change that would allow the use of higher watt seconds for non long arc stud welding, how would I go about this? I would need to address Code: B31.1, B31.3, Section 1, section VIII all divisions, BPV 1 etc.

Thanks again

RE: Thermocouple and pin capacitor discharge welding

I would start with BPV I or BPV VIII, Div 1. You can submit a request for code revision to the ASME Secretary for the standards committee of interest. If you have a copy of either Code book section, the process for code revision is explained.

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