Addressing corrosion in wastewater plants

Corrosion-resistant floor grating and hand railing solutions are indicated for use in the wastewater treatment (WWT) industry. These include mild steel galvanised, 304 stainless steel, 3CR12 stainless steel and fibreglass options; all ideally suited to the extreme conditions in wastewater facilities.

Mentis

The presence of air-borne hydrogen sulphide (H 2 S) can cause severe corrosion in WWT plants, which means the correct material must be selected for key infrastructure.

Hydrogen sulphide is an aggressive gas, provoking acid corrosion, called hydrogen sulphide corrosion. Reacting with water, a natural ingredient of any WWT plans, it forms sulphuric acid and releases a significant amount of molecular hydrogen gas, which penetrates into steel and cases severe damage. Sulphuric acid on its own is a danger to most common metals.

Wastewater can become anaerobic or septic as it travels through sewer lines, due to metabolic processes in the microbes it contains. When dissolved, oxygen becomes depleted in this way, certain sulphur-reducing bacteria thrive and produce the corrosive H 2 S. Among the most common steel infrastructure elements in wastewater plants are floor grating and hand railings. Of these, ordinary steel and even some grades of zinc-plated steel are highly susceptible to acid attack.

Floor grating and hand railing in the WWTW sector.

Stainless steel far more resistant to chemical attack Fortunately, a commercially viable workaround to this problem comes in the supply of railings and other infrastructure elements made of stainless steel, which is far more resistant to chemical attack.

We asked Lance Quinlan, national Technical Sales Consultant at Mentis, to comment. He notes that safety is a primary concern in WWT facilities, especially where there may be toxic conditions within wastewater conveyance and treatment facilities

He further mentions that certain grades of galvanised mild steel, 304 stainless steel, 3CR12 stainless steel and fibreglass options are all acceptable solutions to ensure the safety of plant workers under the extreme conditions in wastewater facilities.

‘These products are designed and engineered to suit situations like these, where the strength to weight ratio is important,’ Quinlan says. Mentis Rectagrid RS40 40/40 floor grating, for example, is engineered with a pressure

Floor grating is manufactured using a pressure locking system.

locking system that guarantees the structural integrity of the product.

Quinlan points out that the transversals on the floor grating are permanently locked to the bearer bars. The locking method at the intersections is designed to use the full depth of the bearer bar when calculating loads. ‘Load-bearing capacity needs to be prioritised in the design and manufacturing of these products,’ he says.

Quinlan highlights that vapours, water and chemicals can create slick underfoot and handhold conditions for operators and technicians. Moreover, this hazard can occur near large machinery and tanks. This creates a considerable safety risk where hand railings and floor gratings are weakened by corrosion and damp.

In addition to using corrosion-resistant material, the stainless steel tubular hand railing systems need to be designed so that moisture drains from the stanchion itself.

‘Our galvanised stanchions measure 42.8mm diameter by 2.5mm wall thickness. The 3CR12 or 304 stainless steel options – polished to a satin finish – are 44.5mm diameter and 2mm wall thickness,’ says Quinlan.

Quinlan stresses the importance of giving individual attention to each wastewater application before products are specified.

Stainless steel tubular hand railing.