In recent years, because of the expansion of the chemical process and pharmaceutical industries world-wide and increased concerns for safety and quality control, Pfaudler began investigating new approaches in glass development that would lead to a glass composition that could be made available to all users of glass-lined equipment.
U V PATEL COLLEGE OF ENGINEERING Page 104 Together with the chemical process industry and with the co-operation of Pfaudler divisions around the world, Pfaudler established the criteria for a new composition:
A non-crystalline structure.
Increased resistance to acid and alkali corrosion. High resistance to impact.
High resistance to thermally induced stresses.
A formulation that could be easily produced by all Pfaudler manufacturing plants.
The result is Glasteel 9100®, Pfaudler's first "international glass", offering an unmatched combination of corrosion resistance, impact strength, thermal shock resistance, non- adherence and heat transfer efficiency.
Now GMM Pfaudler customers, regardless of where their processing operations are located, can purchase a single glass system and be assured of getting the same high quality worldwide. With Glasteel 9100 ®, GMM Pfaudler sets a standard the world can depend on.
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.
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Water
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.
Alkalis
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.
U V PATEL COLLEGE OF ENGINEERING Page 106 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.
Pfaudler Ultra-Glas 6500 ®
1 . Extends the range of Glasteel® applications.
2. Allows safe and easy handling of high temperature processes never before approved for Glasteel equipment.
3. Provides potential for reduced cycle time compared to conventional vessel glass.
4. Provides extended thermal shock protection for faster heating and cooling.
5. Provides increased operating safety margin through its enhanced thermal protection.
6. Is ideal for the higher temperatures required by today's chemical process applications.
U V PATEL COLLEGE OF ENGINEERING Page 107 The features of GMM Pfaudler Ultra-Glas 6500 ® are the result of changes in glass composition and material preparation, altered applications and firing procedures, as well as changes in equipment design and materials of construction. These changes permit trouble-free application of the required high-stress coating and provide the highly corrosive-resistant glass-lined surface for which Pfaudler has been respected for years. Technical details of corrosion rates in common chemicals and thermal operation limits are available on request.