Harris Stay-Silv 15 (part number 15520S) is a phos-copper silver brazing alloy classified AWS A5.8 BCuP-5 — the industry standard for air conditioning and refrigeration copper-to-copper brazing. The 3/32 in square x 20 in (2.4 mm × 508 mm) rod format provides precise alloy metering and easy handling on production lines and service jobs. Stay-Silv 15 contains 15% silver, 5% phosphorus, and 80% copper. Its broad melting range (1,190–1,480 °F / 643–804 °C) makes it forgiving when filling wider joint clearances, while its moderate fluidity (rating 3) ensures the alloy flows predictably into tight capillary gaps. The phosphorus content acts as a self-fluxing agent on copper-to-copper joints, eliminating the need for separate flux in most copper brazing applications. Complies with AWS A5.8, ASME SFA-5.8, QQ-B-654A BCuP-5, EU REACH, and RoHS directives.
| Property | Value |
|---|---|
| AWS Classification | AWS A5.8 BCuP-5 |
| ASME Specification | ASME SFA-5.8 BCuP-5 |
| Other Standards | QQ-B-654A BCuP-5; ISO 17672 CuP 284; BS 1845-CP1 |
| Silver (Ag) | 14.5 – 15.5 % |
| Phosphorus (P) | 4.8 – 5.2 % |
| Copper (Cu) | Remainder (~80%) |
| Other (Total) | 0.15 % max |
| Solidus | 1,190 °F (643 °C) |
| Liquidus | 1,480 °F (804 °C) |
| Melting Range | 290 °F (161 °C) |
| Fluidity Rating | 3 (moderate — good for wider clearances) |
| Rod Form | 3/32 in square × 20 in (2.4 × 508 mm) |
| Part Number | 15520S |
| Flux Required (Cu-Cu) | Self-fluxing on copper — no separate flux needed |
| Flux Required (Cu-Steel) | Yes — use Harris Stay-Silv White Flux; also use Safety-Silv 45 for steel |
| Recommended Joint Clearance | 0.002 – 0.006 in (0.05 – 0.15 mm) |
- Air conditioning and refrigeration (HVACR) — the primary market for BCuP-5; copper tube-to-fitting joints at evaporators, condensers, accumulator lines, suction/discharge connections
- Plumbing and piping — copper water lines, in-floor radiant heating systems, and solar thermal collectors requiring stronger joints than tin-lead or lead-free soft solder
- Electrical bus bar fabrication — joining large-diameter copper conductors and bus bars in power distribution equipment
- Heat exchanger manufacturing — copper tube-to-header connections in commercial and industrial heat exchangers
- OEM copper assemblies — compressor discharge lines, liquid line sets, filter-drier connections, and suction accumulators
The phosphorus in Stay-Silv 15 reacts with surface oxides on copper, producing copper phosphide that acts as a built-in cleaning agent — eliminating the need for an external brazing flux on copper-to-copper joints. This makes Stay-Silv 15 (BCuP-5) faster and cleaner to use than silver alloys (BAg series) for HVACR copper work. Important exception: Never use BCuP alloys on steel, stainless steel, or cast iron. Phosphorus forms brittle iron phosphide at the joint interface, which can cause immediate or delayed joint failure. For copper-to-steel or steel-to-steel brazing, use Safety-Silv 45 (BAg-5) or Safety-Silv 56 (BAg-7) with Stay-Silv White Flux.
Use an air-acetylene or oxygen-acetylene torch. For small copper fittings (3/4 in and under), air-acetylene provides sufficient heat and reduces the risk of overheating. For larger copper assemblies (1 in and above), oxygen-acetylene delivers faster, more focused heat. Apply heat to the fitting body (the thicker component), then sweep to the tube to achieve even temperature before applying the alloy. Feed the alloy into the joint gap from the opposite side of the flame to ensure the metal is drawing the alloy by capillary action rather than melting it directly.
- BCuP-5 (Stay-Silv 15) — 15% silver provides better ductility and service performance in vibrating systems (AC/refrigeration compressor lines). Wider melting range is more forgiving for variable fit-up clearances.
- BCuP-2 (Stay-Silv 0 / Harris O) — silver-free, lowest cost; higher melting range (1,310–1,475 °F). Best for large copper-to-copper joints where ductility is not critical.
- Does Harris Stay-Silv 15 require flux?
- Self-fluxing on copper-to-copper — no external flux needed. For copper-to-steel joints, use Stay-Silv White Flux; or switch to Safety-Silv 45 (BAg-5) to avoid brittle iron phosphide.
- Can Stay-Silv 15 be used on steel?
- No. Phosphorus in BCuP-5 forms brittle iron phosphide on ferrous metals. Use Safety-Silv 45 or Safety-Silv 56 with brazing flux for any steel or stainless steel application.
- What is the brazing temperature of Stay-Silv 15?
- Solidus 1,190 °F (643 °C); liquidus 1,480 °F (804 °C); 290 °F melting range.
- What AWS classification is Stay-Silv 15?
- AWS A5.8 BCuP-5 / ASME SFA-5.8 BCuP-5. Also QQ-B-654A BCuP-5 and ISO 17672 CuP 284.
Browse the full brazing alloy collection. See also the Harris Stay-Silv 15 flat rod — 5 lb tube (15620F5) for high-volume jobs, and the Harris Safety-Silv 45 (BAg-5) for brazing steel and stainless steel. Specification reference: Harris Products Group and AWS A5.8.