What gas would cause ABS to dissolve?

[wiednhft]

What gas would cause ABS to dissolve?

 

I investigated a simple home water toilet shutoff valve that failed, causing significant water damage. When I inspected the 14 year old valve I found that the plastic shaft (that you turn to shut off the water to the toilet) had been entirely dissolved away, allowing significant water to be released into the room. The same type of valve in another bathroom was also partially dissolved. But similar valves for the sinks in the house showed no such degradation.

 

The difference between the sink valves and toilet valves? The toilet valves were chrome plated brass. The sink valves were brass, unplated.

 

The plastic exposed to the water (inside the valve) was not attacked, only the plastic outside the valve body that was exposed to air. There was no evidence of significant water leaking out of the valve onto the plastic shaft.

 

The (Gilbert, AZ) water system contains the following: Chloride 170 ppm, CAC03 17.5 gr/gal, Iron 0.15 ppm, Langlier index -2.21, pH 8.5, Sodium 370 ppm, sulfate 110 ppm, Alkalinity 170 ppm.

 

I speculate that impurities in the water are reacting with the chrome, releasing a gas that attacks the plastic.

 

Any ideas as to what reaction that is causing this?

[vedmecum]

What is ABS ?

[Cap'n Refsmmat]

Acrylonitrile butadiene styrene, I'd guess.

[Moontanman]

If I had to guess I would say chlorine did it. Over time chlorine will erode most white or clear plastics.

[CaptainPanic]

Wikipedia says the following about stability/reactivity:

 

ABS polymers are resistant to aqueous acids, alkalis, concentrated hydrochloric and phosphoric acids, alcohols and animal, vegetable and mineral oils, but they are swollen by glacial acetic acid, carbon tetrachloride and aromatic hydrocarbons and are attacked by concentrated sulfuric and nitric acids. They are soluble in esters, ketones and ethylene dichloride.

 

The aging characteristics of the polymers are largely influenced by the polybutadiene content, and it is normal to include antioxidants in the composition. On the other hand, while the cost of producing ABS is roughly twice the cost of producing polystyrene, ABS is considered superior for its hardness, gloss, toughness, and electrical insulation properties. However, it will be degraded (dissolve) [5] when exposed to acetone. ABS is flammable when it is exposed to high temperatures, such as a wood fire. It will "boil", then burst spectacularly into intense, hot flames. (Source)

 

Wikipedia does not list any reaction that is likely to occur in the environment you described. I also don't know of any reaction.

 

Are you sure that we're dealing with a reaction, and not just a puppy that wanted to chew on something? It sounds like the parts that were "eroded" were exposed to air, so some animal can have had access to it?

Rats can also chew through pretty much everything.

[nitric]

it seems to be a internal water valve, i hope puppies are not part of the water contaminants . As i see it, it is just a plastic being degraded by aqueous chlorine