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Localized Corrosion Issues

The corrosion of steel piping and its related components are a continuous and virtually unstoppable process. Only fire presents a more potentially damaging threat to the operation of a commercial building. In its less serious form, corrosion can produce problems ranging from lost heat transfer efficiency and constricted pipes – to annoyance pinhole leaks and temporary shutdowns.

In extreme, but all too common examples, the failure to recognize and address a serious corrosion problem often results in a major pipe failure, loss of system services, high replacement costs, and legal liability. For New York City properties, the age of the structure has a significant impact regarding pipe condition due to the various changes in construction and materials which have taken place over many decades.

The age of a building property often defines the grade of pipe material used, it’s schedule or beginning wall thickness, corrosion susceptibility, and the general conditions under which natural deterioration has taken place.

Having provided piping evaluations at hundreds of commercial building properties throughout New York, we find that most piping systems can be roughly categorized based upon their age and/or an understanding of specific systems and common corrosion trends.

For properties constructed prior to the 1950s, the use of extra heavy wrought iron pipe was almost exclusive throughout many piping services such as steam, steam condensate, domestic cold water, fire protection, and condenser water. Investigation into the condition of those properties typically finds such pipe to have corroded to the point of existing at standard wall thickness specifications today, and of providing still long service life.

The piping installed has become thinner, however, over time. Beginning at around 1965, extra heavy pipe was often replaced with lighter standard or schedule 40 carbon steel except in certain areas such as steam, steam condensate, and condenser water service. Soon after, at around the 1970’s, the use of extra heavy pipe was removed from most condenser water and steam condensate installations in favor of thinner standard or schedule 40.

With more effective chromate corrosion control treatments being phased out in the early 1980’s, this period of time also saw significant rise in corrosion rates against steel condenser water pipe which was now inherently more vulnerable due to its lower wall thickness. A major influx of poorer quality foreign steel piping in the 1980’s only added to the general rise in overall corrosion rates.

This trend to demand the same reliability and service life from piping systems having inherently less wall thickness, but existing under greater stress and corrosion conditions, changed once again in the 1990’s, with the more common use of extremely thin wall schedule 10 steel pipe in some condenser water and fire protection systems. Whereas a 1940s property having an 8 in. fire standpipe riser would typically begin with an extra heavy wall thickness of 0.500 in., that same piping system today will often have only 0.188 in. of steel originally, yet exist under far greater corrosion threat.

Time itself is often a limiting factor for a piping system. Specific age related problems exist at cast iron waste and vent lines, which offer not far beyond 75 years of service. Brass, commonly used for older domestic hot water systems, corrodes evenly, but is susceptible to the loss of zinc – thereby making it brittle and subject to failure. Galvanized steel pipe, commonly used for domestic cold water and fire protection services, also offers only 60-75 years of service before producing random failures.

Evaluating a piping system for corrosion activity and remaining service life is possible through various methods, although only ultrasonic testing offers the accuracy, ease, coverage, and cost-effectiveness necessary to produce a thorough and reliable result. Corrosion coupons, the most commonly employed form of corrosion monitoring for cooling systems, can under report corrosion activity 100 fold since they exist outside the piping system and are thereby unexposed to the many environmental factors present in typical piping system. Advanced electronic probes, which offer far greater accuracy, are limited due to their high cost, installation requirements, and frequent maintenance demand.

Ultrasound is the proven technology of sending a high-frequency sound wave through the external wall of the pipe in order to measure its wall thickness. The process is totally nondestructive, extremely accurate, requires no shutdown, no cutting of pipe, and provides immediate results. For the same cost of cutting out and replacing one section of 10 in. steel pipe for metallurgical analysis, ultrasonic testing can provide virtually the same information at 50 pipe locations – thereby offering significantly higher assessment reliability. Combined with statistical analysis, ultrasound provides an even more thorough evaluation whereby trends within the piping system can be revealed.

Whether defining an existing corrosion problem, planning for a capitol chiller replacement, or acquiring a new building property, ultrasound consistently provides the best possible investigative and assessment tool.

CorrView International, LLC is headquartered in New Jersey, and offers ultrasonic testing throughout the United States and Canada. We offer further information on ultrasonic pipe testing, an extensive listing of technical bulletins on various piping and corrosion problems, and an introduction to our new patented corrosion monitor.

Questions regarding any corrosion problems are welcomed (available time permitting).

© Copyright 2024 – William P. Duncan, CorrView International, LLC