What Does Disbondment Mean?
Disbondment is a type of corrosion protection involving metals in which a loss of adherence between metal substrates and cathodic coating occur due to a reduction reaction in the coating’s interface. Typically, systems for cathodic protection are installed to support coating imperfections.
Such systems can also react with coatings through physical and chemical phenomena. This could result in the coating’s cathodic disbondment. It must be noted that corrosion may take place within a disbonded coating.
Disbondment is also known as cathodic disbondment.
Corrosionpedia Explains Disbondment
Protection current that is cathodic in nature and travels through metal leads to hydrogen release, which causes coating disbondment. The current only travels through metals within a coating fault, and its density is based on the locally available current and the coating fault’s size. When the current passes through the metal coating, the voltage drops as the interface also reduces. In turn, the equilibrium is achieved in a slight increase in extra disbondment. If there is no presence of coating fault, disbondment does not take place.
There are several factors that affect cathodic disbondment, including:
- Product formulation
- Percentage of cure
- Coating thickness
- Temperature during application
For instance, low temperature application will most likely give a reduced cure degree, which in turn causes low disbondment performance. Cathodic disbondment is also more stable at thicknesses higher than 200 µm. Thus, thickness of more than 200 µm should not be employed if high-performance cathodic disbondment is needed.
In order to evaluate the level of cathodic disbondment, tests are required. This method for disbondment evaluation is especially applicable to pipeline coatings. Good results or low radii of delamination means that the coating is not particularly vulnerable to delamination when cathodic protection is in place.
Such tests can be employed to assess and evaluate barrier coatings' performance in the long run. These coatings are typically used on metal pipes found in underground systems. Generally, the test involves placing the test specimen coated with anode of magnesium as a portion of the galvanic cell. The electrolytes may consist of different salts such as:
- Potassium chloride
- Sodium bicarbonate
- Sodium chloride