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…