Corrosion on bare piping and CUI take on multiple forms and vary in how aggressive the corrosion advances.
Generally, blister rust is the most concerning. Therefore, if your piping shows layers of peeling rust (or ‘blistering’) the corrosion is advanced, and the remaining wall thickness is likely not suitable for operation. Contrary to blister rust, pitting and swelling rust both look severe, though oftentimes the piping can remain in service.
Pitting corrosion is the most common form of corrosion found in refrigeration systems – it is usually a slow process causing isolated, scattered pits over an area. Pitting can be measured. However, measuring the pit does not provide accurate wall thickness or loss measurements due to variables such as pipe age and allowable manufacturing tolerances.
Where corrosion is present, remaining pipe wall must be measured to make an accurate assessment of priority. Subsequently, all pipe should be cleaned of corrosion and coated to protect from future effects of moisture and/or its environment.