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Pipe Substitution

The finding of substantially thinner pipe intermixed with heavier pipe of the correctly specified ASTM wall thickness is not uncommon.  The typical scenario is for an ultrasonic testing investigation to show generally uniform results when suddenly pipe wall thickness plummets to suggest a major corrosion threat.

A worse event is to discover the issue following an unexpected piping failure.

In reality, however, it is not some localized severe form of corrosion activity, but the substitution of schedule 40 pipe for schedule 80 in a high pressure steam service line, schedule 10 or schedule 20 substitution for a schedule 40 condenser water line, or schedule 7 substitution for schedule 10 in a fire sprinkler system.  Ultrasonically measuring dramatically different but uniform wall thickness at each side of the weld joint between adjacent sections of pipe is irrefutable proof that pipe substitution has occurred.

• A Side By Side Example

In the photograph at left, an ultrasonic piping investigation into a high corrosion condition unexpectedly revealed multiple examples of substantially thinner schedule 20 pipe installed into an otherwise specified schedule 40 condenser water piping system.  This was ultrasonically proven by the dramatically different wall thickness measurements at both sides of a weld seam.

Ultrasonic testing also identified areas of deep wall loss throughout the entire condenser water system to suggest severe corrosion and pitting activity likely resulting in a high tuberculation condition.

One run of 12 in. diameter pipe having a suspected schedule 20 length was removed to confirm the findings made ultrasonically.  In addition to proving that the piping contractor had installed schedule 20 pipe in this and in other examples showing similar low wall thickness, visual inspection dramatically highlighted the threat due to tuberculation and deep under deposit corrosion.  While pitting had only a low to moderate impact against the heavier schedule 40 pipe still having a wall thickness of near 0.345 in., a much greater level of threat was demonstrated against the the thinner schedule 20 pipe having an original wall thickness of 0.250 in.

Wall thickness at areas of schedule 20 pipe was approximately 30% that of the schedule 40 pipe due to the random deep pitting activity against already thinner pipe.  (This photograph also shows the direct proportional relationship between the volume of tuberculation and the degree of pipe wall loss below it.)

Although the overwhelming majority of this 28 floor 12 in. condenser water piping system was still suitable for service, deep pitting, acting against thinner pipe in some areas, ultimately defined its future service and led to its replacement.  Ultrasonic testing confirmed the client’s worst fears that they had a severe pitting condition, and then amplified that fear with a finding that substantially thinner pipe had been randomly substituted by the original mechanical contractor.  Furthermore, it was unreasonable to attempt to ultrasonically test every single length of condenser water riser pipe across 28 floors to identify the schedule 20 installed, and less feasible to consider replacing only those sections.

In the above case, rehabilitative actions which may have been possible to clean and extend the service life of system could not be employed due to the far greater vulnerability of the heavily deteriorated schedule 20 pipe.  As a result of this finding, and following additional pipe failures, the entire condenser water system was replaced.

• The Problem Varies

The extent of material substitution may be one single section in the entire piping system, multiple random sections representing some percentage of all pipe, specific areas installed by a different contractor, or the entire piping system itself.

Although not the subject of this Technical Bulletin, other forms of pipe substitution occur by the introduction of foreign pipe where only domestic products have been specified, or where ERW welded pipe has been installed in lieu of seamless ASTM A53.  Rarely is smaller diameter pipe installed, but we have also documented such events – actually reducing the 4 in. run-out piping to all A/C package units to 2 in. but insulating it with 4 in. fiberglass covering to conceal the substitution.  Aside from simple unintentional error, the obvious reason for any known pipe substitution away from the formal design specifications of the project is always a cost savings to someone.

The substitution and installation of heavier pipe also takes place, but rarely.

In general, the larger the piping project, the greater the interest becomes to reduce material costs through wholesale piping supply brokers having multiple sources of lower cost pipe from throughout the world.  Being supplied with pipe from as many as 18 different countries into one project, as we have documented, completely eliminates any expectation of a uniform corrosion history and reliable service life.  It is difficult enough to ensure that the pipe specified by the mechanical engineer has in fact been delivered, although a further interest or recommendation to mechanical design engineers would be to define a minimum of sources or manufacturers as well.

• One Thickness Specification Typically Dominates

For any building piping design, the pipe specification is uniform in terms of pipe schedule at any one pipe diameter; varying only based upon pipe size.  For fire sprinkler systems, the entire piping layout may be specified as thin wall schedule 10, but having heavier schedule 40 installed underground, and at its smaller threaded run-out lines to the sprinkler heads.  Only for very high pressure piping systems at office buildings 55 floors or greater, where pressures may reach 450 PSI or more, might a mechanical engineer specify pipe having a higher wall thickness at the lower floors, and then lighter pipe at the upper floors.  Very rarely, however, are different piping schedules specified for the same pipe diameter within the same building property.

At the former NYC World Trade Center, double extra heavy 30 in. chill water pipe of 1.4 in. thickness wall thickness was specified in the basement pump room operating at 750 PSI, but then reduced in steps as the pipe traveled upward and pressures decreased.  In contrast, for a large manufacturing plant having approximately the same length of pipe horizontally and all at the same low pressures of possibly 65 PSI, only one thickness specification would exist.

• Rarely Checked Details

Even though most building projects have a construction manager, and multiple layers of supervision to ensure conformity with the design plans of the project, the substitution to thinner pipe occurs surprisingly too often.  Steel pipe of the same nominal size has the same outside diameter (OD), with the inside diameter (ID) changing according to pipe schedule.  A favorite selling point of thin wall schedule 7 pipe, for example, is that it flows a greater volume of water due to its larger inside diameter.  No one seems to consider, however, that with a fixed outer diameter and larger ID, something else has to be reduced in size.  Once pipe is installed, its original specification is hidden except if pipe stamps exist.  After it is painted or insulated, that evidence also disappears.

ASTM, the American Society For Testing And Materials, requires each section of pipe to be marked to define:

The name of the manufacturer
Type of pipe such as seamless, ERW welded, or continuous welded
Pipe schedule such as schedule 40, schedule 10, or XH
Specification number such as A53 Grade B or A795
Length

• Removed Or Concealed

For most steel pipe produced today, the country of origin is also provided; with American companies always proud to provide such identification.  Pipe stamps are very helpful in defining what specification of pipe has been provided, but not its quality nor true wall thickness.  Any pipe section showing no pipe stamp should be immediately suspect to its origin and quality.  ASTM pipe stamps are typically stenciled on with paint, and can easily be removed or selectively edited with solvent.  For pipe which is located at ceiling level or where it is not easily accessed, turning the pipe stamp away from view provides even an easier alternative to concealment than solvent removal.

In the example at left, every length of galvanized dry fire sprinkler pipe installed at the 20 ft. ceiling level was oriented straight up in order that its blue “Made in Thailand” pipe stamp remained hidden from view to anyone walking below.  In this example, all three pipe sections to this tee had their pipe stamp oriented at 12 o’clock.

In all lower areas of the building the easily visible Thailand pipe stamps were removed, likely using some type of solvent.  Far above the walkway, however, an easier alternative to conceal the origin of pipe where the building design specification strictly mandated “USA Only” products was to simply turn every section of pipe so that its pipe stamp faced a direction no one would ever be expected to see or inspect.

Of the approximate 50 lengths of pipe at the 20 ft. ceiling level, every single one was oriented with its bright blue Thailand pipe stamp facing directly upward, in conflict with the contractors explanation and legal argument that such orientation was simply a random chance event, and that no effort or intent was made to conceal a direct violation of the piping design specification.  Foreign pipe from Thailand was only discovered following our ultrasonic investigation as the result of multiple piping failures just 1.5 years after the dry fire protection system was installed.

• An Impossible “Mistake”

The presence of thin wall pipe substituted into a heavier specified piping system should be immediately noticeable to anyone in contact with the installation of that pipe.  ASTM 12 in. schedule 40 pipe has a weight of 53.52 lbs. per linear foot, whereas the same diameter in schedule 20 pipe has a weight of 33.38 lbs./ft., – significantly less.  ASTM 6 in. schedule 40 pipe has a weight of 18.97 lbs./ ft., whereas schedule 10 has a weight of 12.92 lbs./ft.  Clearly, watching a pipe fitter pick up and carry an 8 ft. length of supposedly 6 in. schedule 40 pipe over his shoulder is a first good clue that thinner pipe has been delivered.

Aside from weight alone, mechanically joining pipe differs based upon its thickness schedule.  Welding requires beveling the butt ends, which produces a noticeable difference in their dimension between different pipe schedules having different wall thickness.  Since its inside diameter varies according to schedule, pipe sections can only be aligned according to their outside dimension.  Grooving the pipe for clamped fittings also differs according to pipe schedule and therefore difference in wall thickness again becomes immediately apparent.  In short, it would be virtually impossible for any qualified and competent pipe fitter to install different pipe schedules side by side and not be aware and knowledgeable that thinner material was being installed.

• The Weakest Link

Once a finding is made to the installation of thinner pipe, all future service life expectations must be based upon the conditions found at that thinner pipe exclusively, as illustrated at the first photograph above.  The finding of just one example of thinner pipe in any application always suggests that other examples exist, whether due to error, carelessness, or intent.  The greater the number of examples found, the greater is the probability of further pipe substitution.  Other than ultrasonically testing each and every length of pipe, often an impossibility itself, there is no method available to determine where additional examples may exist.

Assuming that corrosion activity has impacted all pipe similarly, a thinner pipe schedule having substantially less wall thickness by as much as 50% or greater will reach its minimum allowable thickness limit faster, and of course – fail first.  A higher 5 MPY corrosion rate acting against schedule 40 condenser water pipe having a wall thickness of 0.280 in. and low pressure may still last 56+ years.  Yet that same corrosion level acting against a section of thin wall schedule 10 pipe having a wall thickness of 0.134 in. will only last 27 years, and surprise everyone when that first failure occurs.  Each example of thinner pipe immediately represents the commonly recognized scenario of the “weakest link of the chain,” upon which higher service life estimates for other areas of the piping system become irrelevant.

For any larger piping system layout, for insulated piping systems, and especially for those where the pipe is concealed behind structural walls and thereby inaccessible, fully defining all examples of pipe substitution within a system is an impossibility.

• Vigilance

Guarding against this threat requires some added attention to detail during construction.  Following the construction period, and especially following a piping failure, the time has well passed to avoid the problem.  Although ASTM pipe certifications may be included in building submittals and other required documentation, they are still general material assessments relating to random lot testing and do not define the source or physical properties of every pipe section supplied to the project.  An ASTM , FM, or UL pipe stamp showing a wall thickness dimension, “0.375 wall” for example, in reality means nothing.

Multiple opportunities exist to avoid the problem beginning at the pipe supplier and extending ultimately to those welding or fitting-up the pipe on the jobsite.  The pipe supplier, mechanical design engineer, mechanical contractor, project manager, construction manager, fabrication shop, cost estimator, shop forman, and each and every pipe fitter – each and every person will come in contact with information that will quickly red flag piping materials either outside the specification for the project, or sub-par in its physical specifications.

Deliberate pipe substitution, whether by the contractor, piping distributor, or pipe supplier, will always be covered by the submission of the proper piping credentials.  In some examples, investigation into the source of uniformly thinner pipe has revealed some “value engineering” decision at upper management levels, and after submittals of the proper piping documentation has occurred.  Today’s mechanical contractors and their pipe fitters, in contrast to those decades ago, show little interest in the quality, thickness schedule, or country of origin of the piping products they install.

A simple hand held dial caliper is the easiest safeguard to ensuring that each section of pipe meets the project specifications – not only according to what pipe schedule has been provided, but also to whether the wall thickness meets minimum acceptable limits according to ASTM for that size specification.  For seamed or ERW pipe, a close look inside each end will reveal whether the longitudinal seam is incomplete and that the pipe should be rejected outright.  Missing pipe stamps provide a most immediate red flag for closer inspection to its origin and quality.

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