By William P. Duncan
From the August 2017 Issue
No other component of a building structure is more critically important, yet less frequently used, than its fire protection system. Designed and installed for a purpose feared and hoped by everyone to never occur, fire protection systems must be ready to function flawlessly as intended many years into the future.
Helping to ensure its life saving operation are high quality mechanical and electronic components that are regularly inspected and tested to ensure their proper functioning. Yet its largest component—the fire pipe itself—stands out as the single greatest unknown. Assumed to bring water to the fire on demand, the naturally present and always hidden threat of pipe corrosion can render an entire fire protection system, and all of the safeguards designed into it, totally useless.
The potential for accumulated rust to stop water flow during a fire emergency has been sadly proven by prior events. Most evidence of corrosion, however, is discovered during renovations, repairs, or other maintenance functions requiring disassembly of the system.
Whether revealed as the result of a leak (as seen in Figure 1), or by the low wall thickness measured through an ultrasonic inspection in Figures 2 and 3, such corrosion-produced restrictions to water flow can occur.
Evolving from the earliest fire protection designs comprising a central standpipe riser with multiple fire hose connections, modern day automatic fire sprinkler systems have grown more specific in their functioning, and significantly more complex in their design and operation.
Piping has also changed, although in an entirely negative direction. The use of thinner piping materials, ERW seamed pipe, threaded thin wall pipe, undersized pipe, and generally lower quality pipe having increased susceptibility to corrosion—all such factors have significantly lessened the reliability of a fire system’s arguably most critical component.
For the same system, there are often different interests and concerns.
While the primary concern for all fire protection systems is its proper functioning during a fire emergency, reality exists to secondary concerns of water damage should the pipe itself fail. To a nursing home, their fire protection system represents life saving insurance. Yet to a worldwide financial institution, the same fire system may be viewed as a potential $1 million per minute loss should corrosion related pipe failure occur above their critical data center servers.
Fire pipe inspection, therefore, is often tasked with answering multiple questions from different perspectives:
- What is the condition of our fire lines?
- What and where are its vulnerabilities?
- How much longer will each zone provide reliable service?
- Is there any threat to water flow?
- Why did our system leak?
- Was our recent pipe failure an isolated incident, or something worse?
- Is limited or full pipe replacement required?
While the internal visual inspection of a fire system will provide the answer to whether a specific section of pipe is restricted or clogged due to corrosion, it offers nothing else. In some instances, the information presented can be misleading.
The observation of mild internal surface rust may indicate no possible interference to water flow, yet still represent a threat to a schedule 10 threaded branch line having very limited wall thickness at its thread cut. Visual evidence to a single rust barnacle at galvanized steel pipe may be viewed as insignificant, yet actually indicate an impending failure due to the deep pitting it represents.
Corrosion’s impact, both in its potential to create high internal rust deposits or cause a piping failure, varies dramatically depending upon whether the pipe is:
- Thickness Schedule 40, 10, or ultra thin wall 7
- Black or galvanized steel
- Threaded, clamped, or welded
- Rolled or cut grooved
- Wet or dry
- Vertical or horizontal
Ultrasonic Pipe Inspections
For many investigations of pipe spanning not only fire but all services, attention is often directed to the most easily accessed areas rather than those of greatest potential vulnerability. Removing clamped sections of smaller three inch pre-action line far downstream of the valve, while easier due to its reduced size, will not reveal the often greater deterioration at its eight inch supply main where it is subject to far greater deterioration due to trapped water.
Since visual inspection is incapable of providing any information relating to pipe wall thickness, and is rarely employed to the extent required to produce a thorough and reliable piping assessment, it is more appropriate as a confirmation to suspicions raised during an initial ultrasonic survey.
Ultrasound, or UT, is a proven technology that transmits high frequency sound waves through the pipe to produce an extremely accurate wall thickness measurement.
Although incapable of detecting internal rust deposits, ultrasound measures wall loss, which is directly proportional to the volume of such deposits—thereby effectively answering the question. Since it is totally nondestructive, the fire system does not need to be taken off-line, drained, or disassembled. This allows significantly greater inspection coverage well beyond the capability of any visual survey.
While technical proficiency is an obvious requirement of any such UT inspection service, of equal importance is their experience and understanding to the many different corrosion scenarios that commonly co-exist.
Threat Varies By Fire System Type
Fire standpipe systems traditionally exhibit lowest corrosion activity while dry and pre-action systems generate a far greater volume of internal deposits. Wet fire systems present lesser concerns than dry systems, although they may mimic the deeper pitting of a dry system near a high warehouse roof where air remains trapped. Galvanized steel pipe is far less vulnerable to rust build-up, but is more prone to deep pitting resulting in premature pinhole failures.
Dry and pre-action fire systems never fully drain. Therefore, higher wall loss is always identified closer to the beginning of the system and at the larger mains. The absence of drain valves, or lack of maintenance in removing trapped water, always means higher corrosion activity in those areas. The slow drip at the seals to a fire pump, while meaningless in terms of water loss, introduces constant fresh oxygenated water, which in turn accelerates the deterioration of its inlet line.
An effective fire pipe evaluation, therefore, is more of a forensic investigation driven by real time findings, rather than the simple procedure of disassembling 5, 10, or 15 random pipe sections and looking inside to fulfill a code requirement. Critically important, it requires the knowledge and ability to translate a spreadsheet of otherwise meaningless wall thickness values into a reliable piping assessment capable of identifying the potential for flow blockage, the remaining service life of the system, as well as any vulnerabilities.
For a facility manager, the most critical step toward initiating any such investigation is to first review an actual prior report from which the expertise and thoroughness of the firm can be assessed.
The speed and efficiency of a properly performed ultrasonic survey will provide the assurance to whether its most important component will reach a fire when required, and surpass other forms of investigation in terms of thoroughness and reliability. n
Duncan is president of CorrView International, LLC, a Landing, NJ company that performs pipe corrosion testing and monitoring. The company has been involved in the field of corrosion control and ultrasonic testing since 1981, providing services to building owners, mechanical consulting engineers, real estate management firms, and government agencies.
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