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Pipe Cleaning

Dirt, microbiological material, iron oxide deposits and scale will negatively impact almost any piping system if left to accumulate.  It is a naturally occurring problem every building operator and plant engineer will likely face at some point during their career.  In some cases, the problem may be minor enough to not even be realized.  In its worst form, however, corrosion can produce accelerated pipe loss, leaks, and the premature failure of a piping system.

With corrosion always present to some degree, the most common operating problems are usually those associated with deposit build-up, lost heat transfer efficiency, and higher operating costs.  In cases where corrosion activity has been high over an extended period of time, interior deposits can actually accumulate to the point of preventing adequate flow, yet with the more serious threat actually existing due to the loss of wall thickness.

• Deposits Produce Secondary Corrosion Problems

In condenser and chill water piping, an interior deposit build-up as thin as 1/8 in. can provide the ideal environment for under deposit corrosion, cell corrosion and/or microbiologically influenced corrosion (MIC) to develop.  Most often associated with condenser water or open process water systems under certain conditions, MIC is a well recognized threat to virtually all piping systems from domestic water to fire sprinkler service.

The example at left, taken from a case history, graphically illustrates the volume of deposits which can accumulate over time.  Here, lightly scraping an approximate 36 sq. in. section of 8 in. pipe interior produced the volume of iron oxide debris shown, and easily illustrated the potential to clog HVAC and computer equipment and components if allowed to remain.

A rough estimate of deposit volume, based upon the weight of material removed from one localized pipe section, suggested that over 1,500 lbs. of iron oxide material likely existed.

This pipe had been abandoned a decade prior and left drained after providing 35 years of condenser water service.  The known volume of interior deposits made it clear that millions of dollars of new HVAC and computer equipment would be at risk if such deposits were not removed before returning the original 1965 pipe to new service.

Ultrasonic testing showed that the above piping system had deteriorated from schedule 80 thickness specifications to just below schedule 40 at a moderate 5 MPY corrosion rate.  Corrosion activity was generalized at the surface – leaving the pipe in good overall physical condition.  Such a finding is unusual, however, since in most other cases, deep localized pitting is far more common.  For many building owners and plant managers, the loss caused by a high corrosion condition is only discovered after it has progressed past the point where the pipe is now unsuitable for further reliable service.

Interior Deposits Equal High Wall Loss

Heavy Interior Deposits	Underlying Wall Loss

• Strong Chemicals A Potential Threat

Aside from total pipe replacement, removing any long established deposits usually requires a continuing, multistage chemical cleaning program using aggressive and potentially dangerous chemical agents – chemicals which can attack the base metal as well as the problem itself.  Although most such chemical cleaners are safe and effective, some of the worst and most expensive piping failures we are aware of have involved the use of strong acids during on-line cleaning operations.

The fact is that a deposit fouled piping system also defines a physically weakened piping system.  Even though a corrosion failure in progress will take place eventually, a multitude of piping failures occurring throughout a building property, and within minutes of adding an acid or aggressive cleaner to a piping system, is something to avoid by all means.  A “Controlled Disaster,” termed by some chemical cleanout companies to define an anticipated but limited pipe failure threat, is still a disaster by any definition once the water begins pouring down.

Various acids and chelating chemicals do offer great benefit, and often present the only cleaning option available.  This is especially true for more complicated piping layouts and smaller diameter piping.  However, their use requires a careful preliminary assessment of the piping to identify any weakened areas.  Threaded joints are always a concern, as are clamped fittings due to their rubber gaskets.

• No Other Choice

CorrView International, as well as most other authorities, have well documented the relationship between interior deposits and long term leaks and secondary operating problems.  We believe that once iron oxide deposits have been established at the interior pipe surface, there is no benefit from the chemical treatment program now incapable of reaching the underlying steel.  For that reason, removing such rust deposits is mandatory to reduce a further acceleration of wall loss.

The thinking at the operations and management is often different, however, with the concern for preempting a leak condition often setting aside any consideration for taking corrective action.

But while a chemical cleaning may indeed cause leaks, allowing the deposits to remain will produce even greater long term damage.  Some chemical formulations offer safer removal options, and are worth investigating.  Long term methods of deposit removal also exist using filtration, although they will not provide the immediate results often necessary.

Compared to the many chemical options that produce varying results with always a clear threat, one non-chemical method offers perhaps the best and safest cleaning alternative.

• Effective And Immediate Rust Removal

High pressure water jet cleaning is a technology well proven in over thirty years of removing iron oxide and various other forms of hardened surface deposits.  It can safely loosen and eliminate virtually all types of deposits simply through the action of multiple high pressure water nozzles – blasting away all deposits and cleaning the interior piping virtually down to the bare metal.  For the most severe corrosion problems, multiple passes may be required.

Since there are no acids, alkalis or any chemicals used whatsoever, there is no threat of attacking and removing the base metal.  The pressure against the pipe itself presents little if any threat.  Unlike chemical cleaning, which generally requires an extended period of time to dissolve and flush the deposits and then neutralize the system, high pressure water jet cleaning provides instant results – allowing the piping system to be placed back in service immediately.

High pressure water jet cleaning removes the heaviest and most strongly attached deposits via multiple passes of various size water jets – solving problems that would be virtually impossible to address using other physical methods.  However, similar to chemical cleaning, careful preliminary assessment of the piping is necessary to identify any weakened areas.

• Before And After Results

The below left side photograph shows the buildup of rust deposits within a section of 45 year old, 6 in. diameter galvanized steel domestic water riser.  Note the larger and lighter colored iron nodules or tubercles mixed throughout the darker colored deposits.  The right side photograph of the exact same section of pipe shows that all traces of iron oxide deposits have been completely removed after two quick cleaning passes using a 3,500 PSI water jet.  No base metal has been removed from the pipe itself, although the internal zinc protective coating had obviously deteriorated away decades ago.

Mild And Uniform Deposits	Shallow Pits Revealed

Note the widespread pitting of the interior pipe surface which has been revealed following the removal of the interior deposits.  Yet the remaining wall thickness, in this specific example, can be seen as quite acceptable.  Such localized pitting activity is common where deposits have been allowed to accumulate, and is one of the most common causes of pipe failure.  Removing such deposits in order that the corrosion control chemicals can reach the base metal should be considered an absolute priority action for any fouled piping system.

Interior surface deposits can either produce generalized and shallow deterioration of the pipe surface as shown above, or it can produce very deep localized pitting as shown in the below photographs.  Removing a large tubercle revealed two depth penetrations of approximately 0.125 in. and 0.075 in., with virtually no other corrosive attack anywhere in the immediate area.  Such a corrosion scenario is far more threatening since all potential corrosion activity focuses at one or a few surface locations.

Heavy Isolated Deposits	Hidden Deep Pitting

• Actual Case History

A major television news network’s planned move into a Times Square building property hinged upon returning to service its abandoned condenser water riser, and to ensure that the riser would provide reliable service over its planned 20 year lease.  A first step to ultrasonically test the pipe showed that 35 years of use at moderate corrosion rates had reduced the original schedule 80 piping to just below schedule 40 specifications, and that long service life existed well beyond its planned 20 year requirement.  The pipe spanned approximately 20 floors.

An internal examination of the pipe, shown by the top photograph of this article, identified significant rust deposits which were expected to migrate into new studio and computer equipment, as well as accelerate future corrosion activity by isolating the base metal from any chemical treatment benefit.  While the pipe had sufficient wall thickness, it suggested a less than acceptable service life based upon higher corrosion rate estimates.  With immediate results required and with the pipe out of service and fully accessible at top and bottom, high pressure water jetting was recommended.

• Volumes Of Deposits Removed

Entry was made at the top of each 8 in. riser pipe.  Navigating past two 90° elbows proved difficult but not impossible.  A centered water jet having at a pressure of 15,000 PSI was used – instantly removing all deposits.  Its approximate 60 GPM water flow then flushing the deposits down the pipe to discharge into a settling and holding tank at bottom.  Water containing fine dissolved and suspended solids was decanted off the top of the settling tank using sump pumps in order to not move the condenser water rust deposit problem to the sanitary waste lines.

During the cleaning process, small samples of the rinse water were regularly taken and collected into one container.  A sample of that collection is shown below left.  By testing its solids content, CorrView International, LLC estimated that over 2,500 lbs. of suspended material was washed away in addition to approximately 400 pounds of solids collected in the settling container.  Overall, we estimated that approximately 1/2 oz. of iron oxide was removed for every gallon of water used in the process.  The below right side photo, taken after 48 hours of settling time, demonstrates the volume of rust removed per volume of rinse water.

Water Jet Rinse

Rinse Water	Settled Rust Deposits

• Special Requirements

While the benefits are many, high pressure water jet cleaning is, unfortunately, not applicable for all piping applications.  It is best suited to straight runs of vertical piping and to heights not exceeding 300 ft. Given that many site preparations may limit its use, consideration must be made for the following:

• The system must be off-line and completely drained.
• Access must be available either through a sufficiently sized valve, spool piece, header, flanged connection or temporary opening cut into the pipe in order to introduce the cleaning apparatus and hose.
• Multiple access points may be necessary depending upon the piping layout.
• The lowest section of the piping must be open in order to drain the cleaning jet water and the debris which will be removed.  Water volume can be high, exceeding 50 gallons per minute, and must be adequately removed using pumps. Ideally, the rinse water should be drained into a settling and holding tank in order that heavier deposits can be physically removed as solid waste prior to being discharged into the drain.
• The actual water pressure generating unit is substantial in size, and is typically powered by a gas fired motor.  Water carrying lines can reach 500 ft. – which is often enough to reach from the pump head to work location.
• Adequate water supply in the form of a 2 in. fire hose connection is generally necessary.
• Horizontal and vertical lines can be cleaned with equal effectiveness, though with greater difficulty for any horizontal piping.  The water jet is self-propelling over hundreds of feet and will navigate most turns and elbows.  Attempting to navigate past two 90° elbows is difficult and often requires a new access point.
• Chlorinating the water may be advised if microbiological product is known to exist.
• Incorporate a supplemental chemical dispersing agent into the water treatment program.  Combined with filtration, this will help prevent the settlement of any remaining fine particulates, and redistribute settled material for gradual removal.
• Install multiple “spool pieces,” or test sections of pipe which can be periodically removed for visual and metallurgical examination and returned to service.  Spool pieces are ideal for evaluating the effectiveness of any deposit cleaning program.

• Full To Partial Solution

The use of high pressure water jet offers significant advantages depending upon the layout of the piping system.  It can provide an immediate solution to a deposit problem in some instances, or address the majority of a deposit problem for others.  For the most severely contaminated piping systems, it may be the only feasible solution.  Given the high volume of deposits that generally will exist within the larger main lines – a combination of using water jet to clean the larger diameter piping and then a mild chemical cleaner for the distribution lines may be the best alternative to such a problem.

Removing perhaps 80% of the problem from the main lines and risers using water jet will dramatically reduce the requirement for both water filtration and chemical cleaners.  Overall savings are also significant in comparison to the high costs associated with most chemical cleaning agents.

Caution is suggested in contracting such work given that pricing is often based upon some percentage of new pipe replacement, rather than a fair estimate of time.  Most work requires 1-2 days of set-up at most.  Cleaning is often the fastest aspect of the work and would normally take only one day.  Additional cost to the client may be a remote video inspection to verify pipe condition and check the pipe surface to its degree of pitting. Chemical cleaning to remove the finest remaining rust deposits is another potential cost typically related to the actions of the chemical treatment provider.  The above described cleaning of the 8 in. condenser water piping was performed in one day at a cost of approximately $5,000.

© Copyright 2023 – William P. Duncan, CorrView International, LLC