Silver Brazing Copper to Brass: Part QB, or Just Soldering?
A shop must join 1 in copper tube to a cast brass valve body with a cadmium-free silver-based filler rod that flows at about 1200 °F. The joint is a socket-type lap joint; neither the tube nor the body melts. The lead man wants to assign the work to a welder who holds a 6G GTAW qualification on 2 in pipe, arguing that "the card covers all joining" and that no procedure is needed because "it's basically soldering." The customer specification invokes ASME Section IX for all joining on the unit. Separately, the shop plans to re-braze any leaking joints a second and third time without changing any paperwork or notifying anyone.
1. How is this joint classified under Section IX, and what does that classification mean for the welder's card and for documentation?
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It is brazing, so Part QB applies and the welder's Part QW qualification is irrelevant.
- The dividing line is the filler metal: brazing uses a filler whose liquidus is above 840 °F (450 °C) and below the solidus of the base metals, with the base metal left unmelted. Soldering uses a filler with a liquidus below 840 °F. At roughly 1200 °F flow on solid copper and brass, this is brazing.
- Consequences: a brazing procedure specification supported by brazing procedure qualification is required, and the individual must hold a brazing performance qualification. A 6G GTAW card on pipe says nothing about a person's ability to control clearance, flux, and capillary flow in a socket joint.
- Practical checks before work starts: confirm the filler's liquidus from its classification, confirm the base metal combination (copper to brass) matches the qualification, and confirm the brazing process (torch, furnace, induction) on both documents.
2. What exactly must exist before the first production joint, and how does the shop's re-braze plan fit into it?
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Three things, and the re-braze question belongs inside them.
- A BPS backed by a BPQR that records the essential variables for this work: brazing process, filler metal classification, flux or atmosphere, brazing temperature and time at temperature, joint clearance range, and the base metal combination. Qualification means brazing test assemblies and examining them (visual plus sectioned specimens) to the required standard.
- A qualified brazer who has been tested with the process and in the position actually used, with the record certified by the shop.
- Re-braze control: repeated exposure to 1200 °F changes the joint - filler reflow, alloying, possible zinc loss from the brass, and progressive clearance change. Whether re-brazing is allowed, and how many times, must be stated in the BPS and be within what the qualification supports. Running second and third cycles "without changing anything" means production is outside the documented procedure and outside the customer's Section IX reference; if the product needs re-braze, qualify the procedure for it.
3. Mid-order the customer supplies a phosphorus-bearing silver filler and asks for the joints to be made with an induction coil instead of the torch that was qualified. What has to be re-done?
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Both changes hit essential variables, and they hit different documents.
- Filler metal classification change: the brazing filler metal is an essential variable for the BPS. A new classification is not a substitution of equivalent product, so a new BPQR is required, and the BPS must be rewritten around it. Confirm as well that the new filler suits copper-to-brass service and is compatible with the flux or atmosphere selected.
- Process change (torch → induction): the brazing process is an essential variable for the BPS, so the procedure must be requalified for induction brazing. It is also an essential variable for the people, so the brazer must be qualified for induction brazing specifically; his torch qualification does not carry over.
- What does not change: the certification responsibility. The shop still owns and certifies both the new BPQR and the brazer's new performance record, and the customer's request does not remove that step.