Outstanding acid resistance under extreme process conditions is a primary characteristic of Glasteel 9100®. and is a result of a test procedure that includes a parameter especially pertinent to glass-lined equipment in service, i.e. the ratio between liquid volume and the glass surface area. The test conditions according to DIN 51174 (Test Conditions section next page) meet this requirement.

There are a variety of chemicals that will inhibit the corrosion rate of glass. However, these are very recipe sensitive and general statements cannot usually be made. An exception to this are chemistries that involve the element silicon (Si), especially when ionised, e.g. Si, SiO. Relatively small amounts of dissolved SiO can be highly effective in reducing the corrosion rate of the Glasteel 9100 system, thereby greatly extending its usage range. It has also been shown that colloidal silica additions to recipes containing the highly corrosive fluorine ion (F-) can drastically reduce the corrosive rate.

Pure Water
Pure water in the liquid phase is not very aggressive. Its behaviour resembles highly diluted acid and corrodes only the surface layer of the glass ("ion exchange process"). At 170°C, a corrosion rate of 0.1 mm/year can be expected.
But because this water is an unbuffered, pH-unstable system, even a slight alkalization can change the situation. If there is a shift toward higher pH values, the isocorrosion curves for diluted alkaline solutions have to be consulted for orientation purposes.
Glasteel 9100 ® is highly resistant to condensing water vapour. However, to counter the possible danger of the condensate shifting to an alkaline pH, it is recommended that the vessel contents be slightly acidified with a volatile acid, e.g. hydrochloric or acetic acid. It is also highly recommended that the unjacketed top head be insulated or heat traced to reduce condensation formation.

Agueous Neutral pHMedia
With these type media, e.g. tap water, salt solutions, corrosion rate depends greatly on the type and quantity of the dissolved substance. Carbonates and phosphates usually increase the rate while alcohols and some ionic species, e.g. A13+, Zn2+ Ca2+, may reduce it.

As alkali concentration rises, corrosion rate increases. Also, the temperature gradient for alkaline glass corrosion, is steeper. The result is that concentrated alkalis require a more definite setting of the temperature limits.

The corrosion rate of concentrated alkaline solutions cannot be expressed by the pH value alone. For aqueous solutions of alkaline materials with a pH value of 14, the particular concentration must also be considered to establish appropriate operating temperatures. Other factors affecting alkaline corrosion are the specific reaction and the dissolving ability of the chemical, the influence of the nature and amount of other dissolved substances and agitation.

Isocorrosion curves for sodium hydroxide, potassium hydroxide, sodium carbonate and ammonia take into account technically relevant parameters influencing the rate of corrosion; for example, the volume/ surface area ratio, inhibition effects by calcium ions, alkaline concentration and temperature.

Under actual operating conditions, even very slight contamination (tap water in sodium hydroxide, for example) can cause major changes in the rate of corrosion. Other factors, such as product velocity and splash zone, can affect the corrosion rate as well. Due to these interactive complexities, meaningful testing is strongly advised.

To eliminate the influence of the testing equipment on the rate of corrosion, procedures are carried out in polypropylene bottles. For solutions above the boiling point, autoclaves with PTFE inserts were used. By comparing the results with control experiments, it is proven that the testing equipment does not have an inhibiting effect.