What Does Point Corrosion Mean?
Point corrosion is a type of non-uniform corrosion. In point as well as honeycomb corrosion, the metal is deeply destroyed. These are the most undesirable types of corrosion, because even an insignificant loss of metal may cause equipment failure. In this type of attack, corrosion of a metal surface is confined to a point or small area that takes the form of cavities.
Corrosionpedia Explains Point Corrosion
Point corrosion is a localized form of non-uniform corrosion. Point corrosion of copper alloys is promoted in the presence of ammonia; steam with sufficiently high levels of carbon dioxide (CO2), oxygen (O2) or hydrazoic acid (HN3); sulfides in waters and iron oxide from upstream corrosion of iron and steel. The area of greatest concern is where the water is forced to change flow direction, such as at elbows and tees. It exhibits deep, narrow, isolated (localized) corrosion cells that can often cause rapid penetration of the substrate that lead to pinhole leaks that can cause water damage and/or mold growth.
A phenomenon known as touch point corrosion (TPC) causes leaks and failures in piping systems of many refineries and petrochemical facilities. It occurs when a pipe rests on a metal or wooden object, resulting in the potential creation of a corrosion cell. Since the TPC areas are inaccessible, manual ultrasonic thickness readings cannot be performed without lifting the pipe. These lifts can lead to other problems such as dislodging environmentally sensitive materials and/or potentially causing additional damage to the piping system.
When acid-containing gases condense on a steel surface a phenomenon called dew point corrosion can occur. In this case, severe attack can result. It can be found in refinery overhead condensers and in waste incineration plants.