Leak Potential for Different Kinds of Pipe

Sooner or later, every pipe will fail. Whatever the material, whatever the quality, whatever the conditions, nothing lasts forever. The numerous external factors at play - water and soil chemistry, installation errors, and so on - complicate the issue, often making it difficult to pin down any one reason for a particular leak. Knowing a bit about the different vulnerabilities of different pipe materials can help, though - so let's take a look at some of the most common!

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In General

• Any pipe needs to be properly secured and supported by pipe hangers or straps: this will ease stress on joints and help prevent leaks.
• Winters can be tough, and a pipe's life is no exception. Water expands when frozen, creating pressure that is exerted on pipe walls, leading to an eventual rupture. If you live in a cold winter climate, your pipes should already be well-insulated. If you're going to be away from home during a cold snap, it's essential to shut off the water supply and drain any standing water - "winterizing" the pipes.
• High water pressure (anything over 80 psi… and even that's a bit high) can cause problems inside any pipe, and your fixtures as well. This is a particular risk for pipes that are too small for the available supply, and especially so with copper. In its interaction with water, copper normally forms an oxide coating on interior pipe walls, helping protect against corrosion. When the pressure and velocity of water in pipes is too great, it can erode this layer, leaving the walls exposed. As you would expect, this is most prevalent at elbows and tees, where water must abruptly change direction. High pressure can also be responsible for water hammer, which will cause its own problems. Learn how to deal with high water pressure.

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Copper

• Pinhole leaks are small leaks that come about from the process of "pitting corrosion" on the inside of the pipe; this is one of the most common causes of leaks in copper pipes. While the exact causes can be difficult to pin down, they're often related to water chemistry. The corrosion can be a result of well water, acidic water (pH <7), hard water, excessively soft water, and even chemicals added by the water provider. Once a leak actually appears (usually in a horizontal run of pipe), it's likely there's already plenty more interior corrosion to be found.
• Standing water in a copper line can not only begin to corrode the pipe (if the water is particularly aggressive, or contains microorganisms), but in a new pipe it can inhibit the formation of the protective oxide layer mentioned above. The remaining "bare" areas of the pipe's interior are left vulnerable to corrosive water once it starts to flow. This phenomenon has been observed with new homes and apartment complexes whose water was turned on, but were left uninhabited for some time.
• Debris isn't good to have in any pipe (or stuck in screens/aerators), but it poses a particular threat inside copper. Like the standing water mentioned above, things like debris from installation/repair, iron deposits from a rusting water heater, and sediment in the supply can prevent uniform formation of the oxide layer inside the pipe, making those areas more vulnerable to corrosion.
• Joining copper requires the use of flux and solder: the former for cleaning and priming, the latter for the actual joining. With older systems, when too much flux was applied to the pipe, it could run down the interior. Because acids are a key component of flux, this could lead to corrosion in those areas. Code now requires the use of water-soluble flux to prevent this from occurring. Interested in learning how to do this yourself? Read our helpful guide to find out how to properly do this.
• Before it's ever soldered, pipe has to be cut. A bad cut, failure to ream (deburr) the pipe afterward, or too much solder (which can remain inside the pipe) will lead to excessive turbulence in the area - think of a boulder in a rushing stream - that ends in a process called "erosion corrosion". If you've ever seen horseshoe-looking pits inside a corroded pipe, this was the cause. The increase in the water's velocity inside the pipe can also lead to water hammer.
• Some older homes have their electrical system grounded to their copper plumbing system. When this is done incorrectly, stray current can run through copper pipe, hastening external corrosion. It's also possible for DC current from an outside source (like some mass-transit systems) to find its way to a residential copper system; the resulting electrolysis will likewise eat at the copper. Luckily, such electrical-related issues are rare.
• Soil quality can promote exterior corrosion in buried copper pipes. Soil that's high in sulfates, chlorides and other chemicals can attack copper in the right circumstances, as can soil having a low pH. External corrosion that can't be traced to electrical issues may be the result of such soils.

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Galvanized Steel

• Once a standard, galvanized pipes have rarely been used in new homes since the 1960s. The protective zinc layer on the interior of these pipes will erode over time, after which corrosion of the steel can run rampant if corrosion inhibitors are not present in the water supply. Brown water and low pressure are clear signs of interior corrosion.
• Joining dissimilar metals in the presence of water can result in galvanic corrosion, a process in which the more reactive metal corrodes at an even faster rate than normal. In plumbing, this usually occurs with a direct connection between galvanized steel and copper, with galvanized steel being the unlucky one. Most codes require the use of a dielectric union or brass nipple to create a physical barrier between the dissimilar metals, reducing the rate of corrosion.
• Galvanized pipes have threaded ends, and the resulting connections to fittings can be particularly unstable, resulting in rust and leaks. Pay close attention to joints in a galvanized line.

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Cast Iron

• As with the other metals, corrosion is the primary concern for cast iron pipes. While the rust that's produced can itself sometimes temporarily "reseal" what would otherwise be a leak, any rust you see on the outside of the pipe (often in little blobs) is a clear indication of trouble.
• Hydrogen sulfide is a product of digestion, and in the presence of bacteria and other chemicals inside a drain or sewer line, is readily converted into sulfuric acid. Excessive corrosion can result, leading to leaks and weak spots. While there isn't much you can do about this (besides replacing aging cast iron pipes), many water providers do add corrosion inhibitors to the supply to help mitigate the problem.
• Sulfuric acid is the main component of many chemical drain cleaners, and this is just one of the reasons they should be avoided (whatever pipe material is present) - opt to clear drains mechanically with a good drain cleaning machine and proper cutter heads.
• Older manufacturing processes for cast iron sometimes resulted in weak spots and uneven wall thickness, aiding the formation of leaks. When it comes to plumbing materials, it's always important to go with the best available, and this is especially so with a material like cast iron. Short-term "savings" are usually wiped out after the first (of many) service calls.
• Because cast iron pipe can become heavily corroded, it's more vulnerable to external physical damage. A vulnerable pipe hit in the right place by a wrench or bumped out of place during repairs could be enough to cause further damage or a leak. All piping should be properly placed and secured.

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Plastics: PVC, CPVC, ABS

• The overwhelming majority of leaks in PVC, CPVC and ABS are due to improper joining of pipe and fittings. PVC and CPVC require the use of primer and solvent cement (aka glue), while ABS requires only the cement since they are completely different types of plastic. When using these chemicals, read the instructions thoroughly - even something like using too much primer can lead to problems. Do not use glues that are old or have become jellified or stringy, and don't mix old and new product.
• PVC is never to be used for hot water. With continued exposure, it will begin to soften and eventually fail. CPVC and ABS, on the other hand, can handle temperatures up to 200°F and 180°F, respectively. PVC is normally used for supplying cold water to a building or to irrigation systems, but can also be used for DWV (drain, waste and vent) systems. Generally, CPVC is used for hot water applications, and for hot and cold water distribution inside structures. ABS is most commonly used for DWV.
• Overtightening plastic fittings can easily crack them, which leads some to PTFE tape or pipe dope in their pursuit of a tight seal. Unfortunately, such products are intended for use with metal threads, and often lead to leaks when used with plastic. Soft-set, paste type, thread sealant compounds approved specifically for use with plastics are available instead.
• Code usually prohibits the use of female-threaded PVC fittings in water supply piping: water pressure is exerted outward, which can easily crack the relatively thin plastic of the female fitting. This can also happen when female PVC is connected to male metal.
• When PVC and ABS are installed underground, they should be below the frost line - this prevents stressing the plastic with freezing/thawing cycles. Your local code likely has very specific guidelines for below-ground installations.
• PVC, CPVC and ABS pipe/fittings can be compromised after prolonged exposure to UV light, resulting in a loss of impact strength and resistance - so keep it out of the sun! If plastic pipe is being used for a vent stack popping out of the roof, it's recommended that it get a coat of latex house paint to help prevent degradation. ABS manufactured with UV-resistant chemicals is also available.