Carbon steel pipework: a best practice guide

30 March 2019

Carbon steel is a durable and cost-effective solution when used in a system designed to reduce corrosion risk

Precision carbon steel pipework gained an unfair reputation due to poor product applications – but simple rules in planning, installation and commissioning can make the most of the material’s considerable advantages. CM explains.

Precision carbon steel will work effectively and last for a long time – if handled, installed, operated and maintained correctly. But, like any metal, it is prone to corrosion when the right steps aren’t followed.

A dramatic rise in the price of copper in 2011 resulted in many smaller installers switching over to carbon steel to maintain their margins. The sudden upswing in its use was helped along by the labour time benefits it offers, thanks to the fact that it can be installed swiftly and with no need for hot works, via press-fit installation. Unfortunately, copper’s high price meant that precision carbon steel sometimes ended up being used for the wrong application or was incorrectly handled.

The discovery of pipework corrosion in the heating system at a new critical care unit at Belfast’s Royal Victoria Hospital led to the project being significantly delayed (see below). This led to many rumours and untruths about precision carbon steel’s performance emerging.

The benefits of precision carbon steel pipework

  • More cost-effective than stainless steel and copper (subject to copper prices).
  • Can be connected with press-fitting systems that remove the need for hot works. Systems like Geberit Mapress offer colour pressing indicators to easily identify materials and unpressed joints.
  • Option for external zinc coatings or external polypropylene coating to help prevent condensation.
  • Extremely low failure rate. Carbon steel has been installed in tens of millions of metres of pipework and where it has failed, it has been related to installation, poor commissioning practices, a lack of maintenance, or unsuitable application.

As the price of copper fell back to a seven-year low in 2015/16, some installers switched back to copper. Meanwhile, unfounded concerns about precision carbon steel led others to switch to
cheap, imported mild steel pipework, or more expensive stainless steel.

In fact, carbon steel remains a durable and cost-effective solution – but it has to be incorporated into a system that is designed to reduce the risk of corrosion, as is the case with any other type of metal pipe.

And if corrosion does occur, then it is usually post-installation or usage of the pipework that is the problem, rather than the material itself, argues Antony Corbett, product manager of piping systems for Geberit.

He explains: “Precision carbon steel comes with its own considerations. It is only suitable for specific applications, namely in closed water systems where dissolved oxygen levels should be lower than systems with open or vented tanks.”

Corbett advises that carbon steel pipework should not be installed outside buildings without adequate protection, in open systems, or with excessive water treatment.

“Simply switching to other materials will not address the problem,” he contends.

In fact, specifying a material such as stainless steel or other tubes which meet old British Standard BS 1387:1985 will only move the problem within a system of mixed pipework materials. That’s because pipework corrosion is accelerated through the formation of a galvanic cell, which happens when two metals are physically connected and placed in an electrolyte such as water.

All metals sit on a scale, where some are more anodic and some more cathodic. Because carbon steel is more anodic than copper, corrosion will occur on the carbon steel. But substituting carbon steel for another material like stainless steel 316 is instead likely to move the problem to other components made of brass or copper.

Press-fitting enables simple installation of pipework

Instead, corrosion on carbon steel can be avoided by following a few simple rules to ensure its long life (see box – six steps to preventing corrosion). That includes keeping the pipework dry during transportation and before installation, ensuring the system it is used in is closed, and filling a system only once when it is commissioned.

Ongoing water monitoring is also crucial. More traditional methods of testing closed water systems haven’t always proved that effective. Ultrasonic thickness tests cannot monitor an entire installation and are therefore unlikely to find a problem before failure, while manual testing offers only a snapshot and can be cost-prohibitive.

But there are now much more efficient, cost-effective digital water monitoring devices that can be sited throughout the system to monitor all materials and produce early warnings of a problem. The devices can also be removed and replaced without needing to drain down the entire system.

“It needs to be realised that the materials are not the cause of failure, just simply an early evidence marker that something is awry,” says Corbett.

“We’re working with specifiers, contractors, and operators to highlight the benefits of precision carbon steel and to reinforce the fact that following a few simple rules through planning, transport, storage, installation, commissioning and maintenance can help to ensure a long system life.”

The free white paper can be downloaded here:

A tale of two hospitals

Pipework installation can make all the difference to project delivery

Royal Victoria Hospital, Belfast (above)

The opening of a new £150m critical care unit at Belfast’s Royal Victoria Hospital, built by main contractor McLaughlin & Harvey and mechanical subcontractor Vaughan Engineering, hit significant delays in 2012 after the discovery of corroded pipework during final checks. The discovery resulted in bad publicity that caused a decline in the specification of
press-fit precision carbon steel pipework throughout the UK.

McLaughlin & Harvey settled its legal action against insurer Allianz in 2016 over the contract, after a judge was told the contractor was left to pay for problems for which it was not responsible. Problems with draining and ventilation in parts of the critical care unit mean that it won’t be fully occupied for another two years.

Omagh Hospital (above)

After the issues at the nearby Royal Victoria Hospital, it was crucial that the consultants involved with Omagh Hospital, once again built by McLaughlin & Harvey, made the right decisions over the closed system pipework. Fortunately, contractor R&F Mechanical had a good understanding of precision carbon steel, its properties and performance benefits and knew how to store, install, commission and maintain the system to avoid any potential corrosion issues.

Geberit Mapress carbon steel was used in full across nine plant rooms in varying diameters of 15mm-108mm. In total, 50km of pipe were installed and at its busiest, 150 M&E installers, all of whom had received training on Geberit Mapress carbon steel, were on site. The system was handed over with no concerns over corrosion.

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