Exhaust service life significantly affected by metal type, tests show

Bosal reveals that the type of metal used in exhausts plays a 'direct hand' in the lifespan of the product

Exhaust service life significantly affected by metal type, tests show
Bosal's drain hole concept prevents the build-up of corrosion.

Bosal, a supplier of exhaust systems, has illustrated what happens to plain mild steel and aluminised coated mild steel perforated tubes when both are subjected to accelerated life testing.

Earlier exhaust systems were made of plain, or uncoated, mild steel that rusts in a short time period, allowing corrosion to take place.

To improve product lifespan, material specifications now include aluminised coated mild steel.

It is a superior grade of mild steel, a process involving cold rolled metal sheeting being hot-dip coated with an aluminium-silicon alloy which oxidizes to protect the underlying metal, in a similar way to galvanized metal.

Aluminised coated mild steel

The above process allows the steel to be far more resistant to corrosion and heat than normal mild steel.

In the early days, exhausts were made of uncoated mild steel inside and out before being externally painted, with annual replacement being the norm.

In a series of tests carried out by Bosal using constant humidity salt spray, it demonstrated how the design and material of exhausts systems has evolved to extend the life of the product.


Evidence of corrosion

The figures above show that the mild steel corroded around the perforated area.

The coated steel has some salt markings and slight corrosion starting around the punched holes on the lesser coated steel.

This was to be expected, as the hole when punched out will lose the coating on the exposed parent metal of the hole.

There is also the question of how thick the aluminised coating is and what degree of protection it supplies, which was addressed through testing a second level of aluminised coated perforated tube.

The aluminised coating offers a degree of protection to the parent metal – the holes are still visible with no loss to the tube integrity.

There’s not much difference in the two different weights of coating.

On the other hand, most of the perforated holes on the mild steel sample are now closed or blocked by the expanding corrosion and the holes that remained were, for the most part, significantly reduced in diameter.

If the mild steel perforated tube was to be used in an exhaust, the results would be an increase in noise and backpressure as well as premature structural failure and poor fuel economy with the possibility of engine damage.

Drain hole concept

In conjunction with its corrosion resistant aluminised coated steel it uses both in and outside its exhaust systems, Bosal has introduced a drain hole to its rear silencer boxes.

The drain hole is a formed 2mm hole at the bottom of the inlet endcap of the lowest part of the exhaust system, to prevent the build-up of corrosion and prolong the life of the exhaust, making it resilient to even the most salted roads.

For further information on Bosal, follow the ‘more details’ link below.

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