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Quotes - Engineering - SalesWhy the braze filler is the whole question
A brazed plate exchanger has two wetted materials, not one. The plates are 316L; the joints between them are whatever filler melted during the vacuum braze. On a standard unit that filler is copper, and it touches both fluids at every one of the thousands of braze points in the stack. For water, glycol, oil and HFC refrigerants that is fine. For a short list of fluids it is not, and no plate grade fixes it, because the plate was never the problem. The only answer is to change the filler, and a nickel-based alloy is the first step up from copper.
Three fluids drive the choice. Ammonia attacks copper and copper alloys outright; a copper-brazed pack on an ammonia chiller fails at the joints within weeks to months, and blue-green residue in the oil is the giveaway. Deionized and high-purity water dissolves copper slowly and carries it off as ions, so the loop conductivity drifts and the polishing resin loads with copper. Then there are process fluids where a trace of copper is a contaminant: electronics rinse water, some pharmaceutical utilities, amine solutions, certain caustic cleaners. Nickel braze is the usual choice for all of these; we confirm concentration and temperature.
What it costs. Nickel filler is harder and less ductile than copper, so the joints carry less pressure and shrug off less thermal fatigue. The same plate that holds 435–650 psig with copper is commonly rated a step lower with nickel; the exact figure depends on the plate size and the design, so we quote the rating with the unit rather than let you assume it. Nickel is the dearer metal and the braze cycle differs, so the finished block costs more than its copper twin. It still lives inside the -320 to 400°F envelope and the 1–3 mm channel that rules out fibrous or dirty fluids.
Nickel-brazed units pair 316L plates with a nickel-based filler for ammonia, deionized and high-purity water, and chemistries that dissolve copper; the plate grade itself does not change. Material & Construction explains how the grade is chosen.
Fluids, ratings and the mistake
Fluids that need nickel
- Ammonia, direct expansion or flooded, on either side of the plate
- Deionized, demineralized and reverse-osmosis water loops
- Fluids with a copper ion limit in the spec: electronics rinse, pharma utilities, final CIP rinse
- Amines and caustic solutions that strip copper from the braze points
Fluids that do not
- Plain water, glycol, lube and hydraulic oil: copper braze and the higher rating
- HFC and HFO refrigerants with POE oil: copper is the standard and the better joint
- Chloride water at any level: nickel does nothing for the 316L plate
- Fast thermal cycling: the ductile copper joint takes it with more margin
The one mistake
- Specifying nickel for a DI loop and then piping the loop in copper tube: the copper count comes from the pipe
- Reading the copper-braze rating onto a nickel order; the nameplate figure is usually lower
- Choosing nickel as the premium option on a glycol duty that never threatened the copper
- Treating it as a corrosion upgrade for the plate: it changes the joint, not the 316L
Nickel-brazed build
What a nickel-brazed order carries; the quotation sets the figures for your unit.
| Feature | Typical build |
| Plate | 316L, dual-certified, same chevron pattern as the copper unit |
| Filler | Nickel-based brazing alloy at every plate contact and around the port rings |
| Copper in the wetted path | None; connections in stainless to match |
| Pressure rating | Design-specific; commonly below the 435–650 psig copper-brazed figure on the same plate |
| Temperature | -320 to 400°F envelope, with nickel holding margin at the hot end |
| Channel gap | 1–3 mm, strained fluids on both sides |
| Ammonia service | Nickel braze, stainless stubs, oil return designed into the circuit |
| Deionized water | Nickel braze plus a copper-free loop downstream, or the braze buys nothing |
Questions on nickel braze
No. The failure is chemical, not mechanical. Ammonia forms soluble complexes with copper at any pressure and any temperature a chiller sees, and the braze fillets thin out from the wetted side until a joint opens. Lower pressure only delays the day the leak shows. Every ammonia plate pack we supply is nickel brazed with stainless connections, and the oil separator downstream is specified with the same rule.
Not measurably. The heat passes through the 316L plate, and the filler sits only at the contact points where the chevrons cross and around the ports. Nickel conducts less than copper, but the braze fillet is a tiny fraction of the surface, so the duty for a given plate count is the same within the accuracy of the sizing. What changes is the rating stamp and the price, not the thermal selection.
No, and specifications mix them up. Nickel brazed means 316L plates with a nickel-alloy filler: copper-free, but nickel is still a wetted metal at every joint. An all-stainless pack uses an iron-based stainless filler, so no copper or nickel-alloy braze touches the fluid. If the standard reads copper-free, nickel satisfies it; if it bans nickel-alloy braze, only the stainless filler does.
Plan on the quotation, not the copper catalog. The same plate commonly drops a step from its 435–650 psig copper rating when nickel brazed, and the drop differs with plate size and the temperature at which the rating is taken. On an ammonia evaporator at 30°F the saturation pressure is low and the margin is wide; on a hot-side duty near 400°F it is worth checking before the system design pressure is fixed.
Whenever the loop has a conductivity or copper spec it must hold. Resistivity loops at 1 megohm-cm and above pick up copper from a copper-brazed pack fast enough to show on the monitor, and 18 megohm-cm polished water shows it within hours. Softened water used as plain cooling water does not need it; RO permeate with no purity spec still leaches the copper joints, so we quote nickel there too.
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