Non Metallic Lining Stability During De-Pressurization

Without knowing the process, what material the coating is made from, the wetting fluid or the temperature (will the stuff boil on depressurisation <rhetorical question - NNTR>?), the best bet is to maintain a dialogue with the companies that are providing the equipment. These people have a commercial reputation to maintain; CR4 readers don't.

Since you're merely considering a coating, I would suspect that you are being forced to utilize the lowest-price option in spite of the fact that this might be a critical application. In such a case, the price may be low but the actual cost in the end could be vastly disproportionally higher

Your fears about any such coating not being effective is well founded. Even cladding has serious drawbacks. What you really should be thinking about is a proper weld overlay of the vessel's interior surface applied by experts. This eliminates any risk of non-integral surface failure which would not only negate the corrosion protection but could also foul your system resulting in production loss or worse. Furthermore, in many jurisdictions this process is a code-accepted means of pressure boundary restoration. Thus, if your vessel is already corroded, this would extend its life.

* By the way, we don't provide such a service. We don't like welding! Our expertise is used by clients who have leakage issues on bolted joints rather than on vessel shells

Interesting question.

Never thought about this.

In ball valves used in high pressure pipelines the O rings are specified as "AED" or resistant to explosive decompression.

In Normal operation the high pressure gas migrates into the Oring and if the pipeline is de-pressured very quickly the high pressure gas inside the O ring kind of explodes

Dear All thank you for your information and suggestions. We have checked with our lining vendors and also searched for industry experience (i.e. SHELL DEP, Technical Papers). It indicated that it is very possible to damage internal coating (blistering & film rupture) during depressurization. The gases that permeated the coating at pressurized condition will expand with decreasing pressure, leading to blistering and film rupture if depressurization is done faster than the gas can diffuse out of coating. Similar effects can occur with water and other small molecular substances if the pressure drops below their boiling vapour pressure. This problem can also occur during Autoclave testing. Currently for our application, vendors are able to suggest compatible coating which can withstand the depressurization and other process conditions.

Samrat,

With all due respect, don't leave yourself at the mercy of coating vendors who will try to do their best to convince you that there won't be problems with this problematic approach.

Before making any commitments I would strongly urge you to become fully versed in alloy weld overlay options. Thermal spraying is simply too risky in my books (and those of many others). Just make sure that you find a fully-qualified vendor. This isn't something that you would want to entrust to a bunch of mere stick-welders. The experts in this field use sophisticated robotic systems. It's really quite impressive, actually. However, more importantly, it's effective.

As I had implied earlier, the initial price will be high but, the overall cost will likely be the lowest of any option (unfortunately many Bean Counters can't understand this logic). It's like shopping for a parachute; you can purchase a very inexpensive cotton version from your favourite tailor (because, after all, it's just a sewing project) or you can pay much more for a fully certified state-of-the art 'chute. It all depends on how safe you'd like to feel just after jumping out of an aircraft, 10,000m above the Earth. I don't know your process conditions. Maybe the apt analogy is only 10cm above the ground and hence it makes perfect sense to give the contract to your tailor. On the other hand, if it's 15,000m...