Potable Water Pipe Condition Assessment For A High Rise Structure In The Pacific Northwest

2. The pipes operate under 2 pressure domains:

• Approximately 20-30 (psi) service
• Approximately 170-190 (psi) pump boosted to upper floors

• 3 Inch main supply lines
• 2-1/2 inch riser lines
• 1 inch multi unit supply
• 3/4 in cold and hot water supply

Sample Limitations: A representative sample would include at least one example of each representative condition.  It would not be necessary to isolate any of the above variables individually because:

• Corrosion is assumed to be uniform as seen in other structures by industry precedent.
• If any unexpected conditions were found, that would prompt follow-on analysis.
• The marginal value of extracting additional samples diminishes after about 6-8 samples.

Introduction of Bias: Some bias was intentionally introduced to the random sample.  None is considered to have an impact on the applicable selection of suitable specimen:

• Necessity to select locations that were easily accessible for the mechanical contractor to extract and repair.
• Necessity to select locations that were minimally intrusive to the residents of the building.
• Necessity to select locations where any possible leak or water spill could be adequately isolated from personal belongings [of the residents] and which could be easily cleaned and drained in the event of a spill.

1. City Water

• ¾” vertical (@Unit 5H)
• 2” Vertical (@Unit 5H)
• 3” Horizontal (@Pump Room)

2. Town Homes

• ¾” Horizontal (@Maintenance Shop)
• 2” Horizontal (@Maintenance Shop)

3. Pump Boost

• 3″ Horizontal (@pump room)

• 1/2” Vertical Hot Water (unit 1D)
• 2″ Vertical (Near unit 16F)

Procedure

1. Initial Planning: Several system isolation scenarios were considered based on impact on the residents vs. system serviceability.  However, due to unknown conditions of the isolation valves, it was considered substantially less risk to shut down water service at the street restricting service to the whole building.

2. Pipe was exposed where needed by a reputable local paint and restoration contractor

3. Water Sample 1 was drawn from sink of unit 1C

4. City Water Department shut the water down at the street level

5. Water sample 2 was drawn from a draining riser in the mechanical room

6. Pipe samples were extracted and repaired by a reputable local mechanical/plumbing contractor over the course of a single day.

7. Each sample was labeled by location, orientation (vertical,horizontal, top/bottom) and direction of flow.

8. Samples were photographed intact upon removal from the system and prepared for shipment.

9a.  Service was restored to building.

9b.  Two leaks and a broken value were discovered as a result of the extraction.  One leak measured at approximately 1 drip per 5 minutes and the other measured 1 drip per 12 minutes.  Root cause was determined and repair was performed two days later resulting in limited service to a single unit (by valve failure) and resulting in an additional building shut down.

10. Each sample was returned to Coles Consultants, LLC  in Seattle.  The pipes were sawn in half in order to expose surface condition and wall thickness (most rust nodulation was knocked off during the slicing process).  Each section was welded to its corresponding half.  Several portions of interior surfaces were mechanically descaled.

11. The valve was disassembled and reviewed for root cause.

12. Sections of the surface were further cleaned with a wire wheel on a Dremel tool.  Specimens where photographed in repose and with a microscope camera at about 50X

13. Findings prepared in a draft assessment and presented to a quorum of the HOA Board and several community members on November 28, 2012.

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Piping Condition Assessment Results

Baseline Water Quality:  A single water sample was drawn from unit 1C and analyzed by Fremont Analytical, Inc, an accredited Laboratory in Seattle.  This sample demonstrated a controlled and stagnant water sample.  A second sample taken from the draining riser is on hold. Additional samples can be taken if deemed necessary in the future with little disruption to the residents.

Water was tested for metals consistent with the active corrosion of galvanized pipe.  The water quality of the City Water Supply is referenced and cited. Of particular concern would be the presence of lead.  While levels are elevated in the sample, they do not exceed EPA maximums [2].

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Note: click to enlarge all photographs below

Baseline Corrosion: All pipe segments demonstrated substantial corrosion and pitting.  It is not possible to measure original material but the wall thickness is presumed to be schedule 40. Larger pipe have a greater wall thickness in proportion to their surface area and are less likely to fail by pitting than smaller diameter pipes.  Larger pipes appear are more likely to grow larger nodules possibly due to lower velocity flow but may also contribute significantly to water quality issues.

 

Figure 1a: All 3-inch pipe showed similar nodulation and pitting.  However, schedule 40 wall thickness leaves substantial material remaining.  The large surface area and widespread rusting would likely be a source of metallic contaminants.  Large nodules break off easily and could restrict flow in elbows, valves and settle in low spots.

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Figure 1b: This section was taken from the 3-inch cold water horizontal line in the mechanical room.  The surface demonstrates heavy growth of rust nodules.  Most of the larger ones fell off during the cutting process.  Note: The side walls show evidence of deep pitting in the wall thickness profile. 

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Medium: 2 inch diameter pipe shows widespread rusting and pitting. Pitting in the 2 -inch pipe samples appear deeper as a proportion of existing material than the 3-inch sections.

Figure 2a: Flow restriction reduce effective bore and promotes turbulent flow which is erosive. Large nodules can break off easily and could restrict flow in in elbows, valves or settle in low spots.

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Figure 2b: This section was taken from the vertical cold water riser at the 16th floor.  Nodules and rust debris dislodging from this height may sink to lower floors or pass into the water system.  Remaining wall thickness is frequently less than 1/2 of the original dimension. Note: shiny areas have been cleaned for inspection.

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Figure 2c: Surface was cleaned with a pneumatic scaler and polished with a wire wheel. Resulting profile demonstrates widespread pitting.  These three examples were found within a larger crater (such as seen in profile view). The diameter of the larger pit shown here is about 1/4 of an inch at widest. 

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Smaller Diameter Pipe:  All 1-inch and 3/4 inch schedule 40 pipe showed widespread rusting and pitting.  Nodules are comparatively smaller but scaling is more apparent.  Pitting is similar in frequency and possibly in depth. However, original wall thickness was much less, therefore, remaining material is likely to be proportionally less as well.

Figure 3a: The following Photographs was taken from the cold vertical section at unit 1D.  The very thin wall section just below the scale is magnified below.

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Baseline wall thickness condition:   The following photographs represent areas that were discovered where less than 1/20 of an inch (roughly 1 mm) or less than 25% of wall thickness material remains.

Figure 4a; a 1 inch diameter pipe showing less than 1/20 inches (1 mm) of remaining material.  It appears that 25%-30% of original material remains.

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 Figure 4b: This wall section of 2 inch pipe demonstrates less than 1mm of remaining material.

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Figure 4c: This 3/4 Diameter pipe with extremely thin wall section, reference figure 3a.  Having found a single section this thin in a random sample suggests the possibility that some leakages currently exist or are imminent.  Less than 25% of original material remains.

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Pipe Threads:

(The subject of vertical riser integrity came up at the HOA meeting; this section was added for supplement)

Pipe threads are cut on a tapered end and are designed to interfere with each other as they are tightened – this is not the same as one would find on a nut and bolt for example.  The pipe thread creates a tight seal and resists loosening because the threads bind against each other.

 Figure 6a shows a typical (not actual) stress accumulation in pipe threads as torque is applied to the adjoining pipes (yellow is highest stress, blue is lowest).  These stresses remain in the steel as stored energy – like a spring can store energy when compressed. When corrosion approaches the thread root a crack may rupture and propagate around the circumference of the pipe compromising the structural integrity.

 

 

Baseline threaded sections: Threaded sections are particularly vulnerable to failure because they are already under a highly stressed interference fit condition, a failure would likely propagate around the circumference of the pipe or provide a path for leakage.

 

Figure 6b and Figure 6c:  Threaded section demonstrating active corrosion near thread root.  Less than 1 mm of material remains.

The following video demonstrates the frequency and severity of pitting in the wall section of 2-inch pipe. When selecting technologies such as epoxy vs repipe, careful consideration should be made for the integrity of the existing material in sidewall thinning and threaded sections

 

Baseline Serviceability:

Valves are useful for isolating segments of the potable water system so that repairs to the plumbing or upgrades to fixtures (and appliances) can be performed without disruption to other residential units.  Further, in the event of a leak, small sections of the system can be isolated for repair and mitigation.  In the event that a valve fails to open or close, the next larger valves in the system must then be used to isolate the line.

This not only impacts more residents, it also subjects the larger valve to possible failure – larger valves are generally exercised  less often and may be more likely to get stuck especially after many decades without use. This makes the whole system less serviceable until eventually, frequent and full-building shut downs may need to be performed to fix minor system problems.

Figure 7a: This valve failed at Unit 1D.  The valve was used to isolate the unit even though the whole building was shut down.  This was done because the mechanical contractors wanted to open the line pressure gradually upon re-energizing the water system ahead of the repair.

 Figure 7b: Only a nub remains. Blue dust is typical of active corrosion in brass. Notable pitting at flange remnant.  This valve was lost long before the mechanic tried to return the system to service.  This condition is more likely than not to exist elsewhere in the system.

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Conclusion

This piping condition assessment is to be used for assessment only.  However, the sampling was performed in such a way that analysis could be followed on, if needed.  The stratified sampling technique was deployed in conjunction with high definition micro imagery and would allow metallurgists to calculate a probable failure date from this report.  However, it is recommended that remediation and system improvement analysis would yield more meaningful results for the community.

This assessment establishes a baseline condition of 1/20 inch (.05 inches or about 1 mm) of remaining material in critical sections of the system.  This assessment establishes three likely failure modes that may arise from the baseline condition.  These include;

1. Failure by corrosion (pitting leaks / thread failure)

2. Failure by non-serviceability (due to persistent valve failure)

3. failure by water quality degradation (rust in pipes, clogging, elevated metals)

The potable water system at this structure is currently stable, but fragile.  Failures by any of the identified modes may be experienced in the relatively near future and it is recommended that remediation is concluded within the next 5 years [6].

Remediation technologies under consideration include pipe liner, copper repipe, and flexible materials such as PEX.  It is apparent from this assessment that some technologies may be better suited for different sections of the system taking into consideration cost vs performance.  Repair and improvement analysis should be pursued in earnest to discover the most efficient strategy to restoring high reliability and water quality to the HOA Community.

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Addendum:

At the HOA presentation, we suggested that the actual practical solution to remediating this large structure while introducing the minimal impact on the residents would be to consider multiple solutions.  

A: Epoxy may be applicable for the large 3-inch pipe since substantial wall thickness material remains and water flow velocities are generally slower.

B: Medium sized pipes (2-inch) and vertical risers could be replaced with copper

C: Small pipe may be replaced with PEX for minimum disruption and cost.  PEX also allows the HOA to make substantial improvements to individual units such as water meters, flow restrictors, central manifold, and improved water distribution system.

The next step is to perform a cost benefit analysis of the various options available to the HOA

References:

[1] On-line Piping Diagrams

[2] EPA Water Quality Standards