High cost of building services corrosion

This Issue This is a part of the Materials performance feature

By - , Build 123

A paper presented to the Australasian Corrosion Association Conference in Adelaide last year suggests an increasing number of building services failures in New Zealand are due to materials degradation.

Many things can cause corrosion of building services such as water supply or disposal, or a heating, ventilating and air-conditioning (HVAC) system. Perhaps the building’s owner, constructor or services designer cut costs at the outset. Perhaps there has not been proper maintenance. Low water quality, inadequate water management protocols or poor commissioning practices in new buildings can also lead to microbiological-influenced corrosion (MIC) in water supply lines.

Dissimilar metal contact and corrosion

HVAC systems are often specified with dissimilar metal contacts. This practice compromises performance from the beginning and suggests HVAC system designers and installers do not understand the principles of corrosion. The paper points out that this isn’t surprising since the ASHRAE Handbook, an internationally recognised resource for HVAC and refrigeration engineering, devotes little space to addressing the corrosion that can occur in building services design. The handbook specifies the use of appropriate materials and advocates treating the water in closed systems with corrosion inhibitors but ignores the problems that can occur if the water treatment programme is poorly managed or neglected.

The paper used the following case histories to illustrate the issue. In each instance, the problem could have been predicted when the system was installed.

GALVANIC ACTION

A care institution installed a low-pressure hot water system for wall-mounted aluminium alloy radiator panels in the residents’ rooms. Corrosion occurred in the radiator panels and they leaked.

The hot water supply system was an interconnected network of copper tubing, steel fittings, copper alloy fittings and polyethylene pipes. The copper tubing and copper alloy fittings in the system released copper ions that initiated galvanic corrosion on the aluminium alloy and carbon steel studs inside the radiator panels. The panel heater design involved contact between aluminium alloy bodies and steel studs in the hot water, which worsened the galvanic corrosion process.

Using dissimilar metals in HVAC systems does not necessarily mean that a galvanic corrosion failure will occur. Dielectric isolators are sometimes used to avoid galvanic corrosion issues, but they can be troublesome to install and are not a substitute for proper water chemistry control. Well managed water treatment with monitored corrosion inhibitors can eliminate the need for dielectric isolator fittings and ensure a long service life for HVAC piping.

In this instance, the design specified the use of a corrosion inhibitor but the water treatment was neglected after commissioning – very expensively, as it turned out.

AGGRESSIVE FLUIDS

A copper-piping network carrying wastewater, sewage, cleaning chemical residues and stormwater to concrete sumps in the basement of a high-rise building showed accelerated levels of corrosion.

In this case, the designer had overlooked the aggressiveness of the fluid inside the copper drainage pipes. There was also dissimilar metal contact between copper piping and steel valves, poorly brazed copper elbows and bifurcated joints showing erosion corrosion due to turbulent flow. Brazing repairs had produced a harmful microstructure in localised areas of the copper piping that contributed to localised internal corrosion.

The system had to be repaired by completely replacing the copper piping with a corrosion-resistant polymer.

MICROBIOLOGICAL ATTACK

An air-conditioning plant providing cool air to a large building complex used a water-piping network constructed from black steel with no internal corrosion protection. The water was sourced from a ground bore, delivered through the steel piping and reinjected back into the aquifer. The water was not chemically treated in the process. In cooler seasons, the air-conditioning system was switched off but was not drained, and untreated cooling water lay in the steel piping during the winter months. After several years’ service, the steel piping leaked and water caused severe damage to retail businesses in the building.

Examination showed that the leaks were due to internal pitting corrosion in the black steel piping. Further microbiological examination found a sulphate-reducing strain of bacteria from the untreated bore supply had colonised the inside of the steel water pipes and caused the corrosion. Hundreds of metres of corrosion-damaged steel piping were replaced with plastic piping at a very high cost, and legal action ensued.

SEA SPRAY

A 40-storey prestige apartment building near the sea had its HVAC equipment located in the plant room on the top level of the building. Rainwater, marine aerosol and birds gained easy access to the plant room through the aluminium-slat dome structure.

Deposits of corrosive sea salt and bird guano contributed to premature corrosion on a variety of surfaces in the plant room, and water escaping from air-conditioning chiller units caused corrosion on the galvanised steel cladding. Paint provided some corrosion protection, but in many places, it had failed after only 10 years. Galvanised steel components performed better, but some galvanised steel fixings had undergone severe surface corrosion. Copper piping fared well. However, due to contact between dissimilar metals at steel flanges, galvanic corrosion had occurred on the steel. Dissimilar metal corrosion also occurred on steel pipes where stainless steel fittings had been welded to the carbon steel pipework.

Little maintenance had been carried out to mitigate the corrosive effects of the marine aerosol on the plant materials.

High cost of corrosion

Corrosion of building services, plant and equipment can be devastating for building owners. Corrosion-damaged air-conditioning coils and heating plant cannot process air and heat as efficiently as the building’s designers intended, and this can lead to greater power consumption, higher maintenance costs and even loss of commercial income during downtime. These factors can also affect the building’s occupants, reducing comfort levels and compromising productivity at work.

Design stage

Corrosion control begins during the design stage of a building project. Good corrosion control requires the awareness and cooperation of the entire design team, including the engineers and designers in each discipline and in overall project management, and post-fabrication cleaning and maintenance of the systems. They must plan and implement ways to collect, report and record any corrosion information that arises during operation once the building is complete.

It is in the interests of everyone involved in the design, build and maintain chain, particularly the building owner and user, that good practice be followed from the building’s conception to demolition.

For more

Fuller information on this topic is in the original paper by Les Boulton of Les Boulton & Associates Ltd, Auckland, in Proceedings of the Australasian Corrosion Association 2010 Conference.

Download the PDF

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Articles are correct at the time of publication but may have since become outdated.

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