Bolted flanges and the trouble of corrosion

Bolted flanges and the trouble of corrosion

When it comes to bolted flanges, some plumbers are choosing to cut corners, which is leading to trouble with corrosion. Johnstone McGee & Gandy Hobart’s hydraulics team reports.


When working onsite, quite often it’s the small details that are overlooked. But some things, as simple as they can seem, could cost you everything.

Following a string of recent issues, it’s worthwhile looking seriously at bolted flanges and the dangers of complacency. Onsite, at an infamous tourist attraction in southern Tasmania, there have been a series of failures in the water main, a section of in-ground pipework where HDPE connects to copper using bolted flanges. Some seemingly small errors in judgement and a few cut corners have led to the repair and replacement of affected pipework, due to the failure of these fittings. In the worst-case scenario, the failure of this pipework could have resulted in a damage bill too unimaginable to put a figure on.

Through an investigation of the failed fittings, it was identified that some poor choices had led to some serious issues. Luckily, the problem was detected in the early stages and reported, as detailed below.

In this case, the flanges installed were Table E eight-hole types, installed with only four bolts. There are four-hole flanges on the market but most are only rated to withstand pressures up to 700kpa. This installation incorporated the fi re line which was set up to be boosted and required to be compatible with pressures up to 1,600kpa.

As the photos indicate, washers were not installed under the bolt heads or nuts. In this instance, galvanised nuts and bolts have been used. Not only are galvanised bolts unacceptable for use in-ground, the absence of washers has meant that as the nuts have been tightened against the sealed surface of the flange, it has removed its protection from corrosion. This has in turn, led to major electrolysis faults in a relatively short timeframe. Also, the flange used was not as specified; installed were the lesser grade ‘standard application’ flanges, not suitable for in-ground usage. At a minimum, the fittings should have been wrapped in a petrolatum tape or similar.

In addition, the backfill used was spoil from a previous excavation; a breach of compliance with the Australian Standard, relating to suitable backfill properties.

Obviously, in this case there have been a string of bad choices made and the installation was doomed from the start. But each of these failings is a danger in themselves. Any of the issues listed above have the same probability alone to cause failure of the fittings, resulting in possibly huge damage to property and public safety. Manufacturers provide instruction to be adhered to; it is the proven method in which they can ‘to the best of their ability’ guarantee that if followed, the fitting is suitable for the stated application.

A red fl ag must also go out for the use of imitation fi ttings, aka ‘the cheaper option’. Known brands such as CTS have a poor opinion of copycat fi ttings attempting to replicate their level of quality, and strongly advise against their substitution. Cutting costs by using cheaper fi ttings can seem clever at the time; but time has a way of revealing complacency and outright disregard for specifi cation and standards.  So, next time you’re onsite, just before you install what has been delivered, it is worth spending the five minutes to double check that the product on hand is suitable for the application and meets the standard specified. Make sure that the bolts are of the correct grade and that you have made every attempt to protect the pipe from corrosion either from aggressive soil types and/or dissimilar metals.

You have been warned…

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