According to the last version of international standard ISO 15589 <Petroleum, petrochemical and natural gas industries — Cathodic protection of pipeline systems>, the guidelines of coating breakdown factor as follows:
 
1.    For onshore sector:

LINE PIPE COATING BREAKDOWN FACTOR PREDICTION

2.    For offshore sector: 

These coating breakdown factors are based on the international standard ISO 21809 serials. These factors are also the foundation of the engineering design of cathodic protection system and are also the foundation of the project design life. The breakdown factors listed above are based on the assumed condition "the quality and performance are fully compliant with the ISO 21809 standard". Reviewing the ISO 21809 standards, we find that ISO 21809 standards do not give a clear picture when the actual pipeline operation is different. 

Therefore, evaluating the breakdown factor for line pipe coatings is the most important step during the engineering stage. Please contact us for further details.