Overwhelming Proof Of A Corrosion Threat Does Not Always Produce The Appropriate Response Preface
A chemical water treatment company acquires a new contract for an older building property known to have not been well maintained or chemically protected. Large rust and scale deposits are found in all strainers and have accumulated throughout the system. The condenser water piping system is fully drained for freeze protection annually, which further suggests a high corrosion loss.
Upon entering their agreement with the building owner, the water treatment representative suggest an ultrasonic investigation of the 50 year old condenser water system in order to learn of any threats potentially impacting their planned chemical cleaning and treatment program.
The chemical treatment company recommends the services of CorrView International, LLC and a contract directly with the building owner is produced. Our investigation shows a moderat to high average corrosion rate of near 5-6 mils per year (MPY) and more severe pitting at the bottom of all horizontal lines likely due to the accumulation of heavy rust deposits. All pipe is heavily impacted due to the fact that it is fully drained every winter season. A visual inspection of a section of exposed condenser water pipe opened in order to attempt to remove deposits interfering with water flow shows approximately 3 in. of rust product at the bottom of the cooling tower supply and return headers.
We estimate that extra heavy pipe was originally installed having an initial wall thicknes of 0.500 in. With wall thickness at many examples of large 18 in. condenser water pipe near 0.200 in., more than half of the pipe in some areas has been corroded away. Identifying some areas of roof level pipe down to near 0.100 in., it becomes clear that the larger main lines will soon require replacement. Still, this finding represents a significant length of trouble free service for a building operating under less than ideal water treatment and maintenance conditions.
Further testing at the individual A/C units served by the main riser produces far greater concern. Here, the 50 year old and originally extra heavy threaded pipe has deteriorated down to near or below minimum acceptable limits. All distribution lines are threaded, which for pipe at 3 in. and 4 in. diameter means a 0.105 in. thread cut loss. After 50 years of service, we identify a substantial number of pipe locations having a current wall thickness of near 0.140 in. or below, and dangerously close to the point where a total pipe separation might occur.
With pressures of near 175 PSI at the lower floors, significantly greater threat is possible due to a 3 in. or 4 in. take-off line separating completely at its threads, in contrast to a pinhole leak at the main riser. Our recommendation is to immediately replace every section of threaded pipe prior to its first reliable isolation valve from the riser, then replace all threaded run-out piping, followed by larger scale planning to replace the main risers entirely. With a large scale project defined, we recommend beginning the replacement of the run-out piping at the lower floors given its greatest and most immediate threat to operations.
The building owner doubts the results of the CorrView report and hires another ultrasonic testing service to check and verify our results. The UT company reviews the 186 page CorrView report consisting of over 75 sets of test data taken throughout the entire building and selects one single area of 18 in. main condenser water pipe for further testing. They take 6 wall thickness measurements in the general area referenced by the CorrView report, and covering approximately 4 ft. of a 18 in. cooling tower supply header.
The company does not measure or identify the lowest 0.102 in. wall thickness documented in the CorrView report within their 6 thickness measurements taken, and consequently produces a scathing report to the building owner totally disissing the CorrView report. No further statistical analysis of the 6 wall thickness measurements is produced, with only a listing of the 6 wall thickness measurements submitted. Results state that wall thickness measurements produced in the CorrView report could not be verified, and that the entire report shuld be discounted as in error.
The building owner submits this critical review to the chemical water treatment company in criticism to their recommendation of CorrView International, LLC, with the letter then forwarded to our office for comment.
We return to the subject property and to the area in question. Within approximately 30-40 measurements and approximately 10 minutes of investigation we again find the 0.102 in. low wall thickness documented in our original report. Further scanning, now approximately 6 months after testing had been first performed, identifies even lower wall thickness measurements of 0.095 in. at this 18 in. condenser water pipe. The very specific areas containing the 0.102 in. and 0.095 in. wall thickness measurements are circled and clearly marked with their dimensions using spray paint. Photographs are taken of the pipe location and its measurements.
A follow-up report is then submitted to the property owner and chemical treatment company documenting the confirmation of our prior findings, as well as even lower wall thickness measurements now 6 months after first measurements were taken. We again state that a failure of the main risers due to pitting will likely be in the form of a small pinhole, whereas failure at the 3 in. and 4 in. threaded run-out pipe to the units is likely to be a catastropic thread separation, and occur at a lower floor operating under higher pressures.
The building owner submits the original CorrView report, the critical review by the other UT contractor, and our follow-up letter to a well known and respected independent 3rd party water treatment / corrosion consultant for his review and recommendations. The consultant, (as CorrView would surprisingly learn many years later in working together at another building property), raises serious concern for their building and reiterates prior CorrView recommendations to immediately replace all threaded pipe as the minimum action required. The consultant emphatically warns to the potential of a catastrophic failure of the condenser water piping.
The building owner discounts the recommendation of the water treatment consultant, and follows the recommendation of a 1 page report based upon 6 wall thickness measurements over CorrView’s 186 page report covering 75 sets of data and an approximate 1,300 wall thickness measurements, and follow-up rebuttal firmly documenting the error by the 2nd ultrasonic testing firm. The building takes no actions to repair the piping.
Approximately 8 months from the date of our original report, on a Sunday night at 2:45 AM, a 4 in. threaded nipple at the main riser separate completely separates to drain the entire cooling tower system through 7 floors of computer room and library storage tenant space on its way to the lobby. By the time the make-up water is shut down and the 18 in. risers drain 26 floors down to the 7th floor, approximately 6 in. of water is in the lobby and cascading out the front doors down the street. The failed pipe section is later shown to be one which had been ultrasonically tested by CorrView and specifically identified in our report as in need of immediate replacement 8 months prior. Damage estimates exceed $900,000, with final damages and lawsuit claims unknown.