For the last decade, the West Coast has experienced a problem with corrosion of domestic water systems. This problem is not due to one or two isolated cases of sub-standard materials or workmanship, but exists in all buildings.

West Coast drinking water, a product of rainwater and glacial run-off, is very ‘clean’. Unfortunately, it is also quite soft (acidic) with pH values typically between 5.3 and 6.3. This low pH causes the copper pipe walls to dissolve from the inside out until the pipe is weakened and replacement is necessary.

Causes of Corrosion

The rate of corrosion depends on six factors:

1. the pH of the water
2. the amount of oxygen in the water
3. the presence of dissolved minerals
4. the presence of dissimilar metals touching the copper pipe
5. the temperature of the water in the pipe
6. the velocity of the water in the pipe.

Water pH

The pH of the water is a prime factor in the corrosion rate and, as we’ve seen, the pH of the GVRD water supply is quite low. There are water treatment devices on the market which allow end users to treat their own water supply; however, Health and Welfare Canada regulations forbid the treatment of a drinking water supply system to an entire building (apartments or condominiums) without the unanimous consent of the occupants. Otherwise, owners of these types of properties can only distribute water as supplied by the GVRD and therefore will inevitably have the problem of corrosion in their copper pipes.

Dissolved Oxygen

Dissolved oxygen in the water will also affect the rate of corrosion. A domestic water supply system (by its very nature) must be an open system and is constantly replenished with fresh oxygenated water. Deoxidizing agents are not acceptable in potable water supply.

Dissolved Minerals

Dissolved minerals within the water (such as calcium) may deposit on the pipe wall and form a protective coating that slows down the rate of corrosion of the copper. Unfortunately, there is a low level of dissolved minerals in the GVRD water supply which could form this coating and so we cannot benefit from this process.

This low level is demonstrated by the mineral residue which forms in a bathtub or shower. In Vancouver, this residue is blue-green because it is mainly copper, which has dissolved off the pipe.

Dissimilar Metals

Dissimilar metals, such as steel, which touch the copper pipe allow electrolytic corrosion to occur which in turn increases the rate at which copper dissolves. This happens most often when copper lines touch steel wall studs, steel pipe hangers, shielded "tech-cable" or when steel pumps or valves are attached directly to copper pipe. Nonetheless, the effects are localized within feet of the contact area and, contrary to common opinion, are not a major cause of the systematic plumbing failures in the Lower Mainland.

Temperature

The temperature of the water in the pipe is important because elevated temperature increases the rate of chemical reaction. Even though there is less dissolved oxygen in hot water than cold, experience shows that corrosion is more pronounced in hot lines. This shows that water temperature is a more significant factor than the amount of dissolved oxygen.

Velocity

A final factor is the velocity of water in the pipe. Water flowing through undersized pipes will have an increased flow-rate. This causes greater "wear" from the suspended solids scouring the inside of the pipe. It also increases the "cavitation" around small discontinuities in the pipe wall (such as pin hole corrosion).

All these factors affect the rate of corrosion. The three related to the content of the water cannot easily be changed by the end user. The remaining three (dissimilar metal content, water temperature and velocity) are a direct result of the plumbing design and installation.

Acceptable plumbing practice in the early 1970s was quite different from acceptable practice today. Bent pipe, undersized pipe, steel valves and motors installed without dielectric unions and heat exchangers sized to output 160°F water are all common in older buildings.

Symptoms

In our company’s experience, the "youngest" building where corrosion required complete replacement was 11 years old. Generally, though, a domestic hot water distribution system will last 20 years, and a cold water system 25 to 30 years. Corrosion typically manifests itself first by pinhole leaks in the domestic hot water return lines, then continues with leaks in the hot risers and finally in the cold risers.

Usually, once the cold risers have reached the critical pin holing stage, the water lines are so weak that any shut-down of the system to repair one area will cause numerous other leaks as a result of the temperature/pressure shock. It is usually best to upgrade prior to this stage.

Each building, of course, is different and must be considered individually. Some buildings show concurrent corrosion in both hot and cold systems while others require complete replacement of only the hot system. As corrosion progresses, the cost of repairs to leaks and the consequential water damage increases until an entire plumbing renovation is economically justified.

Solutions

Traditional renovation was done by teams of plumbers designing as they went. The inevitable result was frayed tempers for both the owner and the tenants as the plumbers ripped apart walls and finishes in search of the risers.  Worst of all, the owner paid through the nose on a cost-plus basis and ended up with exactly the same inadequate system as he had in the first place. It doesn’t have to be like this. Over the past few years, we have achieved relatively painless renovations with minimal inconvenience to the residents and maximum economic cost control for the owner.

Not Magic, But Good Planning

It isn’t magic. Just rigorous investigation and comprehensive planning before a plumber is ever allowed to set foot in the building. In brief, it requires these five stages:

1. Preliminary investigation - is there a problem?
   

2. Investigation - analyzing existing pipe conditions, preparing accurate as-built drawings (no, these are not the same as the original contract set), and redesigning systems to permit local shut-off during the work and to meet modern requirements.
   
3. Preparation of specifications, contract drawings and tender call.
   
4. Contract award, scheduling and field review.
   
5. Contract close-out and commissioning of new system.

There are two points to note. First, the project is designed to be carried out in several stages so that the owner has full control and second, that it’s designed so that the plumbing team is given a full design scheme.

The time to make decisions on pipe sizings or routings (do you go through the tiled wall or the leather-covered one?) is not on Monday mornings when the crew is cranky and up to their elbows in solder.

Type K Pipe

Material costs are a relatively small part of the contract cost and we have made it policy to use type K copper pipe in all our retrofits. Given its 50 per cent greater wall thickness (on average), the longevity benefits are considerable and the cost relatively small. Virtually all the retrofit "specialists" in Vancouver have followed our example and use type K copper exclusively.

Plastic Pipe

Plastic pipe (polybutylene or CPVC) is also an option we use in some buildings. Until recently, the fire code did not permit its use in high rise structures. Today, it is permissible and some advantages exist.

Those installations that suffered some problems, are generally a result of unfamiliarity with the systems and poor workmanship. Despite this, the use of plastic pipe has some real advantages and should be given full consideration in any design. The advantages and disadvantages of plastics are discussed in a later article.

GVRD Policy

Changes in GVRD policy regarding water treatment may also make corrosion a thing of the past. The idea is to change the pH of the reservoirs by adding calcium carbonate, ostensibly to cut down on the amount of dissolved lead in the system. The cost of repairs due to corrosion in the GVRD’s own system may also be a factor. Water treatment in the Lower Mainland is a contentious political issue; however, and it is impossible to predict when, if ever, the GVRD will adjust pH in the reservoirs.

To sum up, copper corrosion is a major concern in all buildings, especially high rises and apartment buildings. There is no magic cure except replacement. The good news is that with proper planning and supervision, the costs are not prohibitive and the project can be finished without paying tenant compensation or without having tenants move out.

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McCuaig & Associates Engineering Ltd. pioneered many of the practices now considered standard in the plumbing retrofit industry. Should you require any further information, please do not hesitate to contact our office. We will be more than happy to answer any questions or concerns you may have.

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