Photo Gallery of Corrosion Types

We offer below an assortment of photographs taken from years of archived ultrasonic pipe testing and remote visual inspection work. These graphically illustrate the various forms of corrosion commonly found at HVAC cooling water and process piping systems.

It can be virtually guaranteed that some degree of certain corrosion types exist at every water circulating system. But while corrosion itself cannot be totally prevented, it can be controlled in order that problems do not reach the level of severity as shown below.


Generalized Corrosion - This 40 year old sample of 8 in. schedule 80 pipe, while clearly containing deposits of iron oxide, shows very even wall loss and long remaining service life. The pipe was cleaned using high pressure water jet and returned to service with approximately schedule 40 thickness remaining.		Galvanic Corrosion - An extremely common problem area due to the failure to install galvanic insulators between carbon steel pipe and either brass valves or copper pipe. Combined with schedule 40 pipe and a moderate corrosion rate, galvanic corrosion will often produce premature failures with 6-10 years.


Under Deposit Corrosion - A condition often indicated ultrasonically by some areas showing at near original specification, and adjacent areas of high wall loss. It is more prevalent at the bottom of horizontal lines, on lower floors, and where flow rates are slowest.		Total Thread Failure - A potentially worst case scenario, this 1 in. take-off line from a 24 in. main condenser water riser corroded completely through and separated. Remarkably, corrosion product within the failed nipple held back 12 floors of water.


Galvanic Corrosion - A combination of water penetration through the roof level pipe insulation and galvanic activity completely dissolved this pipe hanger. Severe wall thickness loss is obvious in the immediate area of the pipe hanger and resulted in the need to replace this pipe.		Galvanic Corrosion - Another example of the higher corrosion activity usually existing at direct brass to black iron connections. At low corrosion rates, galvanic corrosion may be negligible, but usually increases greatly once corrosion rates exceed 5 MPY.


Under Deposit Corrosion - Created by either a corrosion cell or an MIC condition, high wall loss is typically found under interior rust deposits - more commonly called tubercles. Such localized and deep corrosion can easily reach rates of 25 MPY or more, and destroy even larger diameter pipe in 5 years or less.		Insulation / Galvanic - Moisture penetrating through the insulation at this chill pipe provided an initiation to an outer corrosion problem at the steel take-off line. Exterior moisture also assisted in the heavier attack at the threads due to galvanic activity between brass valve and steel pipe.


Under Insulation Failure - The general failure of this fiberglass chill water pipe insulation allowed moisture to penetrate and produce severe pipe deterioration in localized areas. Often seen as exempt from corrosion problems, this copper pipe was severely pitted at its exterior and in need of replacement.		CUI Corrosion - Often identified only after the removal of pipe insulation for another purpose, water from rain and snow typically penetrates most exterior installations to cause wide ranging wall loss. This creates a corrosion problem on two fronts, and can produce severe damage over time.


Localized Pitting - Partially water filled systems produce widely varying wall loss typically along the bottom. For this dry fire sprinkler system, testing showed virtually new pipe after 25 years at the top, shown at the left. The wet pipe bottom however, shown at the right, was totally deteriorated to the point of failure.		Under Deposit Corrosion - The degree of wall loss occurring under tubercular deposits is generally proportional to the volume or size of the internal deposit. A 0.100 in. wall loss can translate into a 2 in. internal iron oxide deposit. This photo illustrates the greater threat of high wall loss over the restriction in water flow.


CUI Corrosion - Roof level pipe often suffers even higher exterior metal loss due to the combined effects of moisture condensation, direct water infiltration, and insulation damage. Such heavy deterioration is usually only discovered after a leak occurs.		Localized Corrosion - A good example showing particulate deposits settling along the pipe bottom to produce deep under deposit pitting. Testing showed the side walls of the pipe near factory specification, but total penetration of the pipe at the bottom and lower sides.


Galvanic Corrosion - Galvanic corrosion is often suspected where the use of schedule 40 threaded pipe is actually the basic problem. While some additional wall loss might be attributed to the attack of the brass valve upon the carbon steel, it is often the 60% loss of pipe upon threading which will cause a premature leak.		Under Deposit Corrosion - The pipe interior does not need to be completely covered with tubercular deposits to produce a severe pitting condition. Here, corrosion cells developed randomly and widely spread along the bottom of this galvanized sprinkler pipe to produce a total penetration of the pipe wall within 2 years.


Pitting Corrosion - The presence of one repair clamp and five nearby pinhole leaks confirms that a severe corrosion problem exists at this fire sprinkler piping location. This is made worse by the original installation of thin wall schedule 10 stock, where little wall thickness loss can be tolerated before reaching minimum acceptable limits.		MIC Corrosion - This photo of the inside bottom of a cooling tower pan shows a severe and concentrated pitting condition. The brown rust ring around each pinhole failure was a natural event of the corrosion mechanism. At the time that this photograph was taken, MIC was the suspected cause of the filure, though not confirmed.


CUI Corrosion - Similar to interior corrosion, exterior pipe corrosion due to moisture condensation can take the form of either deep and random pitting, or, as shown above - a generalized deterioration of the entire surface. Since iron oxide is approximately 25 times less dense that the original steel, it often suggests a much greater wall loss than actually exists. CUI is the greatest threat to smaller diameter piping, but can severely reduce the service life of even the largest sizes.		Under Deposit Corrosion - Six pipe clamps and three active leaks along this one single 18 ft. section of 6 in. condenser water pipe suggested a severe corrosion problem. However no problems were found elsewhere on the same system, and ultrasonic testing failed to identify any significant wall loss. The problem was identified as a buildup of settled particulates in this by-pass line from supply to return, and with the downstream side of the pipe closed only.


Severe Pitting - An unexplained pitting condition produced pinholes throughout this relatively new cooling tower of only a few seasons in service. Destructive analysis of failed sections of the tower pan showed a combination of MIC and metallurgical defect of the manufacture of the steel itself as producing this widespread problem.		Galvanized Pipe- Over 62 years of carrying New York City domestic cold water in this 8 in. galvanized wrought iron line produced this eventual result. UT testing showed deep under deposit pitting well throughout the pipe, and an overall corrosion rate of near 3.5 MPY. Corrosion produced both constricted smaller diameter pipe, and pinhole failures.


Heavy Deposits - A common corrosion result following decades of fire standpipe service. This galvanized steel pipe is barely recognizable as such, and accumulated an overall restriction of approximately 1 in. across this 6 in. diameter ID. Concern was raised once pinhole failures started at the threaded joints, with UT testing showing only 0.050 in. remaining in that area.		Corrosion Under Insulation- High humidity near an outdoor area, combined with a 42 º F chill water supply temperature, thin 1 in. fiberglass, and no vapor barrier reduced the service life of this area of piping to under 8 years. This represented a dramatic loss from other less affected areas of the same piping system - which showed greater than 30 years of remaining life.


Schedule 10 / Pitting - At least 15 pipe clamps over a single 21 ft. section of this 2-1/2 in. pipe suggested a major corrosion problem. Ultrasonic testing, however, identified thin wall schedule 10 sprinkler pipe used in some areas of this condenser water system. In reality, the pipe had provided excellent service over its 18 year history, and had simply reached the end of its useful service life.		Pitting Corrosion - Deep pitting typically shows itself first at the smaller diameter piping simply due to the lower wall thickness present. Such evidence should be taken as an advance indication that a system wide problem likely exists, rather than assumed a localized event. A failure at the midpoint of a pipe section suggests a much greater corrosion problem than one at the threads.


Roof Level Weathering - One of the easiest corrosion problems to avoid but one of the most common, protecting this pipe from external wall loss only requires some regular maintenance. The addition of an unnecessary external corrosion condition will often cut the estimated service life of the pipe in half, and produce unexpected failure. Regular inspection and protective maintenance is required.		Dezincification - Typical surface deposit resulting from the dezincification of brass pipe due to old age and/or an aggressive water condition. Over many years, the zinc component of the metal is leached out to leave copper. Deep pitting is initiated and the pipe becomes porous prior to producing an actual leak, and leaving a corrosion product behind.


Galvanic Corrosion - An extremely common problem for areas where brass or copper is joined to steel. Under certain conditions, as shown here, it may also exist at steel to steel contact points - where new pipe meets old, and where different ground potential exists.		CUI Corrosion - An extremely common problem area in examples where very cold pipe temperatures and high humidity combine under insufficient insulation protection. CUI is a greater threat to chill water supply pipe than normal internal corrosion activity.