The two main categories for mechanical failures are impact and stress.
Impact
Internal impact:
Internal impact occurs when something hard hits the interior lining surface. Generally speaking, you want to avoid dropping any object heavier than 1 lb. from a height greater than 9 inches. When you are working in a reactor, it is important to pad the floor and mixing system before entering the vessel to prevent an accidental internal impact from a loose item or tool that is dropped. Repair for this type of damage involves a 3-piece plug for damage up to 4 inches and a patch for larger areas.
External impact:
While glass is quite strong in compression, it is weak in tension so a direct blow to the exterior of the vessel can cause a “spall” or star-shaped crack pattern to the interior glass lining. Avoiding a sudden external force to the reactor is an easy way to prevent this type of damage from occurring. It can be repaired using the same method used for internal impacts.
Hydroblasting:
Installing a wash-in-place system via spray balls and other type of pressure equipment is an effective way to keep your vessel clean. However, if the high-pressure cleaning exceeds 2000 psi or if the water jet is less than 12 inches from the vessel wall, damage can occur (there are situations where greater allowances are acceptable, but this is a general best practice). Additionally, abrasive particles mixed with the water can contribute to hydroblast damage as can water sprayed on a specific area for a prolonged period of time and direct contact to repairs such as patches or plugs. In extreme cases, the glass lining can be worn down to the steel substrate. Reglassing is usually required to fix this type of failure.
Abrasion:
When particles that are harder than the glass surface contact it, abrasion can occur. This often happens at the edges of nozzles, baffles and agitators due to vigorous mixing. Most abrasive damage is minor and doesn’t require repair, though sometimes polishing may be required, and in extreme cases reglassing may be needed.
Cavitation:
Caused by condensation, pressure decrease, and chemical reaction, cavitation is the damage that occurs when bubbles collapse at the glass surface (who would think that bubbles can generate such an impact force?!). Incorporating Nitrogen into your process can help to subside bubble collapse and using spargers is also a way to combat cavitation. If damage is severe enough, reglassing of the damaged surface (vessel, agitator, and/or baffle) may be required.
Stress
Crushing:
Despite its compressive strength, improper flange makeup and uneven or over-torquing can crush glass. In addition to carefully selecting your gaskets and following proper flange assembly techniques, calibrated torque wrenches must be used to avoid excessive stresses. Epoxy putty is a suitable fix for minor damage. Other repair methods for flanges include outside metal or PTFE sleeves. Extreme cases require inside-outside metal sleeves.
Bending:
When piping systems are not adequately installed and supported, the connection to the vessel is subject to excessive tensile and compressive forces which can lead to bending damage. Bending damage is evident from the cracks that appear at the bending axis. This damage can go as deep as the steel substrate and necessitates the use of an outside metal or PTFE sleeve, or reglassing in severe cases.
Vibration:
When baffles, dip pipes and other accessories that are installed via nozzles are not sized and positioned properly, it can result in vibrations that can cause glass damage so widespread that the only solution is reglass. This can be prevented, however, by properly aligning your agitator and other internal components as well as being conscious of water hammer and using the right sparging device for steam injection.