SettingsSettings for this calculationUS
The metal on one side of the joint.
Neither metal is risky on its own — what matters is the SEPARATION between the two in the galvanic series. Area then decides how fast: a small anodic component against a large cathodic one, like an aluminium fastener in a stainless panel, corrodes quickly because the whole panel drives the small anode, while the same pair with the areas reversed barely reacts. Note which of the two is the small part.
The metal on the other side of the joint.
The pairing only matters where an ELECTROLYTE bridges them. Two metals dry and in contact do essentially nothing; the same two in a coastal atmosphere, or in a lap joint that holds rainwater, react steadily. So the detail matters more than the metals do — an isolating washer, a coating on the cathode, or a joint that drains and dries will change the outcome further than swapping either material would.
Galvanic corrosion risk level
3 Risk Level (1=Low, 2=Medium, 3=High)
This is general reference guidance based on typical galvanic series relationships for common plumbing metals — always use a dielectric union or approved isolating fitting whenever joining dissimilar metals in a wet system, regardless of the indicated risk level, per code requirements in most jurisdictions.
They open the calculator with your figures already in it
Dielectric Union Galvanic Corrosion Risk Evaluator: 3 Risk Level (1=Low, 2=Medium, 3=High) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Show calculation logicHide calculation logic
How this was calculated
Formula source(s)
- Galvanic corrosion risk depends on the two metals' positions in the galvanic series — dissimilar metals far apart in the series (e.g. copper and steel/aluminum) corrode faster when in direct contact with an electrolyte present, and a dielectric union or fitting is commonly used to electrically isolate them. Common plumbing metal-pair risk levels below are general reference guidance, not a substitute for a corrosion engineer's assessment on critical systems.
Inputs used
- First Pipe Metal
- Copper
- Second Pipe Metal
- Steel (Black Iron)
Confidence note: This is general reference guidance based on typical galvanic series relationships for common plumbing metals — always use a dielectric union or approved isolating fitting whenever joining dissimilar metals in a wet system, regardless of the indicated risk level, per code requirements in most jurisdictions.
What this calculation does not cover
- The two metals set the direction of attack; the AREA RATIO sets its speed, and there is no field for it here. All the current leaving a large cathode concentrates onto a small anode, so a steel nipple threaded into a copper system pits through in a season, while the same pair with a large steel body and a small brass insert sits for decades. Copper to steel scores 3 whichever way round it is entered; on site the two cases are years apart.
- Nothing happens at all without an electrolyte, and how aggressive it is changes the whole picture. A dissimilar joint on a dry gas line or in an unheated void never forms a cell; the identical joint in softened, chlorinated or hot recirculating water carries far more current, because conductivity, dissolved oxygen and temperature are the multipliers. A hot return loop is the hardest duty in most buildings and scores the same as the dry one.
- A dielectric fitting interrupts the metal path, not the water path. The water column itself conducts across the gap, so a weak cell can persist through the union, and the fitting's own steel body plus the debris that collects in its restriction is often what fails before the pipe does. Some jurisdictions now favor a length of brass transition over a dielectric union for exactly that reason.
- Galvanic attack is one mechanism, and a score of 1 clears only that one. Dezincification strips yellow brass in aggressive water, erosion-corrosion pits copper wherever velocity runs high or a fitting was left badly reamed, and stray DC from a bonded electrical system or a nearby cathodic-protection installation eats metal with no dissimilar joint involved anywhere.
Add the equipment this sizes
This result is a specification — 3 Risk Level (1=Low, 2=Medium, 3=High) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Galvanic corrosion risk depends on the two metals' positions in the galvanic series — dissimilar metals far apart in the series (e.g. copper and steel/aluminum) corrode faster when in direct contact with an electrolyte present, and a dielectric union or fitting is commonly used to electrically isolate them. Common plumbing metal-pair risk levels below are general reference guidance, not a substitute for a corrosion engineer's assessment on critical systems.
Cite this page
Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.