What Causes Plumbing Pipe Corrosion and How to Spot It

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PVC or polyvinyl chloride plumbing pipe has essentially eliminated corrosion in plumbing supply and drain lines, but plenty of homes still have old galvanized pipe. Copper isn’t immune from corrosion, either, but it’s sometimes easier to spot than corrosion on galvanized metal.

When inspecting the plumbing in older homes or new ones that use copper, be aware that wherever there is metal, corrosion might restrict water flow, contaminate the water or both.

What Causes Corrosion in Galvanized Pipe

Galvanized water supply lines are a distinct problem in older homes built or re-plumbed before the 1960s. It’s virtually impossible to prevent corrosion permanently. Corrosion isn’t just frustrating to live with, it can be dangerous to your health.

All that galvanized (zinc coated) supply lines need is enough exposure to water and ordinary minerals for there to be a corrosive reaction and mineral buildup. Considering that their sole purpose is to deliver and distribute water and most water contains minerals, the materials were a poor plumbing choice.

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Copper plumbing installation, especially at the fittings, requires skill.

If galvanized pipe contacts copper, another problem emerges. Galvanic corrosion happens at the point of contact. It’s not uncommon to see copper-to-galvanized fittings if a novice was the installer.

Why Does Copper Pipe Corrode?

Copper plumbing supply lines can pick up corrosion from rusty water heater deposits, water left standing too long in the pipes or from excess flux left inside the pipe. Flux helps soldered copper joints bond.

Copper can also pick up minerals and develop pits. And if the pipes are exposed to water traveling at a high rate of pressure and speed, they can pit the inside of the pipes and impair water flow.

How to Spot Corrosion or Find Clues if it’s Hidden

Corrosion in galvanized pipe can prove tricky to detect. Sometimes, corrosion is visible on the outside of the pipe. More often, corrosion builds up inside the pipe where you can’t see it. The same applies to copper.

On the outside, corrosion on galvanized pipes looks like clusters of mineral deposits, especially around joints and pipe leaks. It’s often chalky, thick, uneven and an eyesore. In time, the corrosion may turn rusty orange. With copper, corrosion might begin as a green oxidation and advance to deposits, also at leaks and joints.

A classic symptom of corroded galvanized pipe is severely restricted water flow. In some cases, the internal diameter of the pipe becomes so narrow over time that showers are weak, washing machines take too long to fill and garden hoses might only produce a trickle. You can’t always see corrosion, but you can usually find evidence that it’s there.

Metal pipes are always at risk of corrosion when they contact residential water. The zinc coating on galvanized lines doesn’t last forever. If copper and galvanized make contact, both pipes suffer. Copper on its own can pick up corrosive materials from the water. And water traveling through the lines under high pressure can wear away pits in any metal.

If you’re dealing with an older home, corrosion is always a risk. With corrosion comes restricted water flow and in extreme cases, cruddy water. Spot the signs of pipes that have seen better days and you can give customers a heads up about replacement.

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