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Home / News / Industry News / Paint Film Complete After Application — Why Does It Blister in Acid and Alkali Environments?
Industry News
In chemical plant equipment, storage tanks, pipelines, steel structures, and all kinds of heavy-duty anti-corrosion coating systems, a situation arises consistently: the coating is applied and the film is complete, adhesion is good, and the surface is flat and uniform — but after long-term exposure to acidic or alkaline corrosive environments, the coating gradually develops blistering, doming, and even localised delamination.
In most cases, this type of problem is not caused by application quality. It is the result of changes in the coating's internal structure and interface stability that occur gradually under the sustained action of corrosive media.
01
A Complete Film Does Not Mean Stable Acid/Alkali Resistance
In the initial period after application:
- The film is complete and uniform
- The surface is flat and smooth
- Adhesion state is normal
These characteristics indicate good initial film formation quality, but they cannot fully reflect the long-term stability of the coating in an acid or alkali environment. A complete film does not mean that blistering will not occur after prolonged contact with acidic or alkaline media.
02
Corrosive Media Continuously Act on the Film Structure
During long-term service:
- Acidic and alkaline media are in sustained contact with the film
- The coating is subjected to continuous chemical action
- The surface layer structure gradually changes
As contact time increases, film stability continuously declines, and localised areas become more prone to abnormal development.
03
Media Permeation Weakens Interface Stability
A coating maintains its integrity by relying on:
- A dense film structure
- Good interfacial bonding capability
- A stable protective barrier
When corrosive media gradually penetrate into the coating, interface stability may be affected — increasing the risk of blistering.
04
Local Defects More Readily Become Blistering Origins
In actual service:
- Film thickness varies from zone to zone
- Edges and weld seams are subject to complex stress states
- Local positions are more readily affected by media
These areas are often the first to show blistering.
05
Environmental Change Accelerates the Failure Process
During long-term service:
- Temperature continuously changes
- Humidity continuously fluctuates
- Corrosive media act repeatedly
These factors overlap and compound, further accelerating coating ageing and interface destabilisation.
06
The Longer the Service Time, the More Obvious the Blistering
In the early stages of service:
- The film is generally more stable
- Surface change is not obvious
But as service time increases:
- Chemical action continuously accumulates
- Film structure continuously changes
- Localised blistering gradually expands
The blistering phenomenon typically becomes increasingly obvious over time.
07
Why There Are No Problems at the Time of Application Completion
Because at the time application is completed:
- The film has just been formed
- The structure remains stable
- It has not yet been subjected to the long-term action of corrosive media
As long-term contact with an acid or alkali environment continues:
- Chemical media continuously act on the coating
- The interface state continuously changes
- Locally weak areas are gradually exposed
Only then does the blistering problem slowly appear.
Summary
A complete film that develops blistering in an acid or alkali environment is fundamentally the result of the combined action of chemical media, declining interface stability, and environmental factors.
A complete film does not mean stable acid/alkali resistance
Corrosive media continuously act on the film structure
Media permeation weakens interface stability
Local defects more readily become blistering origins
Environmental change accelerates the failure process
The longer the service time, the more obvious the blistering
These factors act together to cause blistering, doming, and even delamination in anti-corrosion coatings in acid and alkali environments. When analysing acid/alkali blistering problems, in addition to evaluating application quality, it is necessary to comprehensively assess the coating system's chemical resistance, film density, and long-term protective stability.
Frequently Asked Questions
Does a denser-looking film always resist acid and alkali blistering better?
Visual density reflects macroscopic film continuity at the point of application, but not the film's ionic permeability or resistance to hydrolytic attack at the molecular level. A film that looks dense can still allow media permeation at rates that lead to blistering over months of sustained contact. Chemical resistance of the resin system, crosslink density, and interface bonding quality are more relevant predictors of long-term performance than appearance.
Why do weld seams and edges blister first even when the flat panel areas look intact?
Weld seams and plate edges typically have thinner film coverage, higher residual mechanical stress from welding, and more complex surface geometry — all of which create zones of locally reduced protective capability. The same media exposure that the flat panel surface can withstand may exceed the threshold at these critical zones, which is why they blister ahead of surrounding areas.
Can blistering in acid/alkali environments be prevented entirely, or only delayed?
Selecting a resin system with genuine chemical resistance to the specific media at the actual service concentration and temperature, ensuring uniform film build at all zones including edges and welds, and providing adequate substrate preparation all contribute to extending the time before blistering appears. In the most aggressive service conditions, periodic inspection and maintenance remain part of the system design.
