Short definition
Galvanized iron pipe is steel pipe dipped in molten zinc for corrosion resistance. From roughly the 1900s through the early 1970s it was the standard residential water supply material in much of the US, including Washington. It’s the defining repipe target in pre-1970 WA homes — the zinc wears off the inside, the steel rusts and tuberculates, and the result is whole-house low pressure and brown-water complaints.
What it is
Galvanized pipe is threaded steel with a silver-gray zinc coating. Joints use malleable-iron threaded fittings sealed with pipe dope or PTFE tape. Walking through an old WA basement, you can spot it instantly: vertical and horizontal threaded steel pipes with a dull zinc finish, often weeping rust at the elbows and tees.
The chemistry is straightforward. Zinc acts as a sacrificial anode, protecting the steel from corrosion as long as the zinc layer is intact. Once the zinc is consumed — typically 40 to 60 years in residential potable service, sometimes faster in soft acidic Pacific Northwest water — the steel begins to rust from the inside. Rust scale builds up as tubercles, choking the inside diameter and dramatically reducing flow.
Why it matters to a homeowner
If you own a pre-1970 Washington home with original galvanized supply piping, you’re on a clock. The classic symptom progression:
- Reduced pressure at upper-floor fixtures while ground-floor pressure seems acceptable. Hot side often goes first because heat accelerates corrosion.
- Brown or rust-colored water on first draw after vacation or overnight stagnation. Anaerobic corrosion product accumulating in the lines.
- Whole-house low pressure — the shower drops to a trickle when anyone flushes a toilet, multi-fixture flow is unusable.
A whole-house repipe to PEX is the standard remediation. Costs in Washington typically run $4,000 to $12,000 depending on access (single-story vs. multi-story, finished vs. unfinished basement), number of fixtures, and material choice. Partial repipes — replacing only the worst sections — are sometimes done as a budget alternative, but they tend to push the failure to the next-worst section within a few years.
When a quote talks about “galv-to-PEX repipe,” “complete supply replacement,” or “tuberculated supply abatement,” they’re describing this work.
Washington note
Galvanized pipe is especially common in Western Washington’s pre-1970 housing stock — the Capitol Hill, Wallingford, Ballard, Tacoma North End, and similar bungalow / craftsman / midcentury neighborhoods. Two WA-specific factors:
- Soft, slightly acidic surface water (Cedar/Tolt, Green River) is more corrosive to zinc than hard groundwater. Galvanized supply piping in Seattle and Tacoma homes often shows symptoms earlier than the national 40-to-60-year benchmark.
- Mixed-metal trouble at copper transitions. Where a previous remodel added copper to a galvanized supply without a dielectric union, accelerated galvanic corrosion at the copper-to-galvanized joint produces a leak or a clog within a few years. Inspecting these transitions is a standard repipe diagnostic.
Common failure modes
- Tuberculation — internal rust scale chokes flow. Cut-out sections show heavy buildup.
- External corrosion at thread joints — pipe is thinnest at the threads; leaks usually start at fittings.
- Pinhole leaks from severe pitting.
- Mixed-metal galvanic corrosion at copper-to-galvanized transitions without dielectric isolation.