 |
 |
This photograph shows large tubercle’s on the bottom area of the pipe with smaller tubercles on the right side of the pipe. There is a definitive water line shown in the lower 1/3 area of the pipe indicating this pipe was flooded for portion of time. Standing water can produce advanced Oxygen Cell Corrosion and Acid Slime Attack in the same general area of Fire Protection Systems (FPS). It was noted during the initial inspection of the piping that Sample 2 had two distinct large pinholes. Sample was cut and processed with sectional cut of the failed area which was then circumference cut and pressed flat to give 360 degree view of the failed area of the piping. Pictured below are the photographs of the sectioned portion of pipe Sample 2.
Sample Photographs Prior to Cleaning:
The complete sectional cut around the circumference of the pipe was then pressed flat and cleaned so microscopic analysis of thepipe could be observed. The bottom portion of this pipe sample was cut so the center area of the photograph is the physical bottom side of the pipe. This is where the tubercle and pinhole damage occurred. This bottom area of the piping revealed 70% coverage of red – brown deposits where water was present and the large tubercles was formed. The lighter areas are where lighter deposit occurred. The large tubercles caused two pinhole failures which are evident from the picture below that shows the pipe sectioned and clened prior to the microscopic evaluation.
The complete sectional cut around the circumference of the pipe was then pressed flat and cleaned so microscopic analysis of thepipe could be observed. The bottom portion of this pipe sample was cut so the center area of the photograph is the physical bottom side of the pipe. This is where the tubercle and pinhole damage occurred. This bottom area of the piping revealed 70% coverage of red – brown deposits where water was present and the large tubercles was formed. The lighter areas are where lighter deposit occurred. The large tubercles caused two pinhole failures which are evident from the picture below that shows the pipe sectioned and clened prior to the microscopic evaluation.
The picture 1A sample was sectioned from pipe Sample 1 prior to, and after cleaning. The cleaned view revealed what looks like “dark clouds” over a shinny surface. The photo is difficult to see without third dimension view. Pictured below is the Microscopic view of that water line area. The dry area, above the water line showed only minimal attack, which is typical of “White Rust and or Zinc Oxide” deposits. This confirms the fact that both received pipe samples had standing water at the air water interface. This photo reveals destructive Oxygen Cell Corrosion which is further enhanced when viewed as digitally enhanced 3D image that is computer generated to show the physical depth of the corrosion at the water line/air interface area. Pictured below is the microscopic view of the corrosion pitting witnessed from sample in the bottom portion of the piping. The deepest oxygen pitting was 42 Mils in depth as compared to typical wall thickness of 120 Mils. This depression in the metal is direct result of Oxygen Cell and Microbiological Corrosion.
Above the air/water interface area an oxide film is partially protecting the metal above the water line which was not subject to metal loss b acid attack. This part of the pipe is in good condition except at the air/water interface. More aggressive corrosion is evident at the bottom portion of the piping where the large tubercle had formed.
Picture 1A and 1B Microscopic view are photos of the Sample 1 piping before and after processing. This piece of processed pipe is from the bottom area of the pipe where the large tubercle was located.
Picture 2B shows the deposit build up caused by Oxygen Cell Corrosion and Iron related bacteria attack in a close up view. Water analysis will confirm this problem.
Picture 3A and 3B are additional photos of the Sample 1 piping before and after processing. This piece of processed pipe is from the bottom area of the pipe where large area of the piping was covered by an Acid slime attack. Smaller tubercles were located throughout the area that was submerged in standing water. You will then see an etching effect in this sample, which is very common in an Acid slime attack. Acid slime attack will appear like river etched into the steel. This is due to the pooling effect of the acids produced by the slime layer that was formed on the bottom areas of the piping. Small Tubercle areas are also visible and are direct effect of Oxygen Cell Corrosion with bacterial attack. Picture 3B shows the cleaned view of the etched area with random pitting throughout the sample. Picture 3B confirms the standing water and the advanced Acid slime bacteria attack. This pitting has penetrated 40% of the wall thickness.
A closer look under the microscope reveals significant pooling of acids produced by the bacteria contamination. This destructive “Acid trenching” can cause premature pipe failure. Pictured below is a Microscopic view of the witnessed Acid trenching. Proper chemical treatment of this sprinkler system should be considered. Chemically treated sprinkler systems can see life expectancies in excess of 150 years while treated.
Summary of Results:
The extensive corrosion observed is being caused by several factors. There are three components necessary to allow this problem to exist. The three component of corrosion are Water, Oxygen, and the Pipe. The rusting process of oxygen rich water reacting with iron started the damage initially. Dry systems are vulnerable due to the presence of trapped water and the fact that these systems operate with pressurized moist air source. The constant daily temperature fluxuations on these systems causes moisture to condense on the internal portions of the piping. Oils left in the piping systems act as nutrient for the bacteria to thrive.
The mineral deposits that dropped out of the solution started the initial Underdeposit Corrosion via “Differential Oxygen Cell” corrosion. Once the Galvanized protective coating has been compromised, the galvanic corrosion process can begin. Differential Oxygen Cell Corrosion followed by additional (MIC) corrosion issues caused the Acid Slime Producing bacteria “Trenching” that was witnessed in the 3B sample. The smaller generalized acid tubercles mentioned above were in the upper water line areas and are Oxygen Cell pits. Some of these bacteria do not like oxygen environments and therefore live in protected tubercles. The Acid bacteria eat chlorides and sulfate minerals in the water and produce an acid excretion in the process. The acid attack under tubercle looks like deep bit cut (steep wall pits) into the metal. The other pits that have gradually sloping walls are where the Acid Slime attack occurs with Oxygen cell corrosion. The generalized greenish black coating on all metals is Ferrous Hydroxide. This product is the beginning process of iron migration that turns to the deep redbrown color where more oxygen can come in contact with it producing Ferric Hydroxide. An “Acid Slime Attack” will produce a channeling effect on the metal as seen in Sample 3B. Iron Related Bacteria will produce an Acidic condition that will accelerate the corrosion process. Slide 3B below shows the bottom portion where the Acid Slime attack is most prevalent. Multiple samples were removed from this pipe due to the unique damage that was observed.
As stated above, the gradual heating and cooling of the fire sprinkler water may have contributed to this depositing process. Microscopic analysis of this slime attack showing the typical trench marking commonly found with an Acid Slime attack area is shown below.
Surface cleaning revealed the damage that occurred under the surface deposits. The majority of damage was Iron Related Bacteria attack and it occurred in the bottom half of the pipe. This is very obvious when viewed in close up as well as viewed under the microscope.
Picture 1A is photo showing capped tubercle containing, white Calcium Carbonates, and Magnesium Silicates, dried acid slime deposit on top of bluish gray Siderite and the greenish black Ferrous Hydroxide; all evidence of pipe attack. This tubercle was 370 mils tall and very active.
We would like to point out that this sample did show deep penetrating damage of 42 mils that did not penetrate the 118 mil wall thickness. The deepest pit completely penetrated the wall thickness of the Sample 2 pipe. The tubercle shown in sample 1A came from the Sample 1 pipe and had a depth that penetrated 36% of the wall thickness on this pipe.
CONCLUSION- Both Microbiological and Oxygen Cell Corrosion are the causes of your pipe destruction.
- Underdeposit Corrosion aided the differential oxygen cell destruction.
- Unstable water conditions in combination with anaerobic producing bacteria likely raised the water pH to produce more deposits.
- Slime forming bacteria formed acids under tubercles that accelerated the pipe failure.
Please feel free to call for our recommendations to eliminate the problem or we will be glad to consult on the specifics should you want to treat this condition. A water analysis will identify the products necessary to clean, disinfect, and provide corrosion protection to protect this system. Thank you for allowing us to be of service.
Very truly yours, Richard P. O'Leary |