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Undersized Steel Pipe

The first use of steel pipe to carry liquids or gas can be traced back to 1815 when an inventor joined together discarded American Revolution musket barrels to transport coal gas throughout London to fuel home lanterns and stoves.  Soon after, in 1825, inventor Comelius Whitehouse designed a process whereby flat steel plate was bent and formed into a rounded shape and “butt-welded” along its longitudinal seam – a process continued relatively unchanged to this day.  The first true manufacturing plant for steel pipe opened in Philadelphia, PA in 1832.

Historically, the earliest non-metal pipe used for water transport was bamboo, dating back to 2,000 B.C.  Greater strength and flow volume demand eventually led to the use of hollowed out tree logs, which were used to construct Boston’s public water supply system in 1652.  Still to this day, examples of wooden pipe are unearthed at older American cities such as New York City and Boston.  While most are out of service, some surprisingly still remain active.

• Standards Developed

With the manufacturing of steel pipe, and of all pipe products actually, formal standards began to evolve to define its physical dimensions as well as its strength, chemical composition, and mechanical properties.  Further requirements for pressure rating, testing methods, product identification, certification, and overall inspection were also defined.

Those standards are today maintained, refined, and published by the American Society of Testing And Materials, ASTM.  Established in 1898, ASTM is the largest voluntary standards development organization in the world; publishing thousands of new standards annually.  Virtually every aspect of pipe manufacture and its certification is defined in the various standards available, and used by pipe manufacturers throughout the world.  Published standards are available directly through ASTM on their website at www.astm.org, or by calling 1-877-909-2786.

• Pipe Specific to HVAC And Fire Service

While ASTM standards exist for the manufacture of every type of piping of varying materials, carbon steel pipe used for HVAC and fire service is generally limited to a few types and schedules.  For HVAC applications, mild carbon steel of ASTM specification A53 is common.  Fire protection systems also employ A53 as well as A106, A135, and A795.  Seamless pipe, which was once the standard, has been generally replaced with electric resistance welded (ERW) or seamed pipe products

For HVAC applications, the majority of pipe used is standard or schedule 40.  For fire protection, thin wall schedule 10 is now the standard for most installations, with examples of schedule 7 and even schedule 5 frequently encountered.  Extra strong or schedule 80 pipe can be found in certain applications, such as for steam condensate lines and under some high pressure conditions.  In contrast to piping systems installed prior to 1940 when extra strong pipe was commonly used for all piping specialties, far thinner piping products are now specified.

• The 12.5% Tolerance Standard

Steel pipe has a very wide 25% manufacturing tolerance of 12.5% plus or minus its ASTM specification.  That means that 12 in. schedule 40 pipe having an ASTM wall thickness specification of 0.406 in. may actually range between 0.3553 in. and 0.4568 in. and still be considered suitable for installation and service.  In reality, no attention is paid to pipe which is oversized, as it provides an added bonus to any building property.  It is only the minimum thickness dimension which is of any concern.

While the 12.5% tolerance allowance is proportional across all pipe sizes and schedules, it has tremendously greater impact for smaller diameter pipe of inherently less wall thickness.  For the above example of 12 in. schedule 40 pipe, its lowest undersized dimension of 0.3553 in., while it represents years of lower service life, still provides substantial wall thickness and no potential threat.  Apply that same 12.5% undersized tolerance to 2 in. schedule 40 pipe having an ASTM specified wall thickness of 0.154 in. and now its wall thickness may be closer to 0.1348 in.

Unlike for welded or clamped piping systems, most 2 in. diameter pipe is threaded, and therefore it loses an additional 0.072 in. of wall thickness at its thread cut.  Whereas 0.082 in. would remain at the thread based upon factory specifications, only 0.063 in. would remain at its 12.5% maximum undersized tolerance – a very significant loss.  Yet, as our investigations have proven in dozens of more recent pipe testing projects, it is not uncommon to find new pipe manufactured to below this 12.5% minimum.

• Changing Times

Until very recently, pipe was commonly produced either at its ASTM specification or above.  For ultrasonic investigations of older piping systems dating 20 years ago and earlier, and where very low corrosion activity has been maintained, it would not be unusual to measure wall thickness still at or above new ASTM specifications under certain operating conditions. Steam piping systems having uniformly low corrosion activity would often produce some wall thickness measurements above its ASTM specification after even 30 years of service to prove that heavier or oversized pipe had been installed.

A recent investigation of 24 in. in condenser water riser at a New York City Rockefeller Center area property from 1959 identified still high wall thickness of 0.500 in. or above in many area. This due to the original installation of extra heavy pipe having a specified wall thickness of 0.500 in., the manufacture of that pipe to above its ASTM defined thickness value, and 54 years of very low corrosion activity well under 0.5 mils per year.

Except for some small diameter threaded lines serving high pressure demands, such high wall thickness numbers are unheard of today given that extra heavy pipe is very rarely installed – even under higher 350 PSI pressures of a 50 floor office building. In addition, corrosion rates have escalated due to greater limitations of the chemical inhibitors to perform, the generally higher susceptibility of new steel pipe to corrosion, and due to the engineering design of some piping systems to produce localized areas of greater deterioration. Add to the above issues the factor of undersized pipe and an understanding develops to the higher incidence of pipe failure problems identified today.

Further add into this equation that much of the pipe installed is from foreign sources widely recognized and proven as being of lower quality and workmanship, and it becomes clear that pipe failures for seemingly no reason actually should have been expected.

• Proof Of Physically Undersized Pipe

Best proof to the issue of undersized pipe is found wherever new pipe is being readied for installation. Samples never having been water filled or placed in service exclude any potential argument that an excessive corrosion rate over the first 6 hours, 6 weeks or 6 months of operation, an issue due to someone else’s negligence, produced the low wall thickness measured.

Although ultrasonic testing is preferred since it can evaluate a greater area of pipe and not just only the ends, a standard 0.001 in. resolution dial caliper is all that is necessary to establish the wall thickness of any pipe section not installed. For dial calipers especially, removing any internal or external burrs or raised edges is mandatory to producing an accurate wall thickness measurement.

As stated earlier, a significant volume of pipe, if not most of the pipe manufactured today, is produced to some degree undersized its ASTM thickness specification due to what we believe are closer production tolerances enabling manufacturers to produce a lighter but still approved product within the tolerable limits of the ASTM code.

Extensive testing of new steel pipe has consistently found undersized material statistically beyond the possibility of being a random event. In remarkably frequent examples, new pipe will be found well below its minimum permitted wall thickness.

It is important to note that an FM or UL approval rating or ASTM pipe stamp does not mean that the pipe is at true ASTM specifications or to within its allowable 12.5% tolerance. Nor does ASTM monitor, approve, inspect, or certify piping manufacture. In short, it is only the quality control of the manufacturer itself which defines whether the pipe is acceptable or not.

Above left we show the test result for a section of new U.S. produced 8 in. carbon steel pipe of the ASTM specification A53 Grade B seamless. Its ASTM specification calls for a wall thickness of 0.322 in., which is likely what design engineers are assuming for this addition to an existing 175 PSI condenser water system.

Instead, we measure a wall thickness of 0.292 in. consistently throughout its length, which represents it being 9.3% undersized. At a typical corrosion rate of 2 MPY, this reduction of 0.030 in. of wall thickness represents a potential 15 years of service lost.

In a second example at left, testing at a section of new 6 in. schedule 40 A53 pipe, with the ASTM specified wall thickness of 0.280 in., produced true wall thickness measurements over its length of 0.248 in., and 0.032 in. below specification. For on-site skeptics at this construction job-site questioning the accuracy of the ultrasonic instrumentation, physical measurement by dial caliper produced the very same wall thickness dimension.

At 0.248 in., this new pipe is 11.4% under its ASTM factory specification prior to even being installed, and again will provide lower than expected service life. Under higher corrosion conditions more common today, such undersized pipe will provide far less service.

Further testing of two other sections of 6 in. pipe from the same HVAC condenser water expansion project, but from a different U.S. manufacturer than the first example, produced similar results with wall thickness dimensions consistently near 0.245 in. – precisely 12.5% under its ASTM specification and at the lowest limit of what is permitted by the ASTM code.

Another example of new 6 in. schedule 40 pipe, installed only 1 week into a condenser water system and in a completely separate project in another state, shows similarly low initial wall thickness of 0.244 in. as opposed to its defined ASTM thickness specification. The pipe stamp defines a wall thickness of 0.280; reality shows 0.244 in.

Not only is this section of new pipe undersized, but it is undersized to 12.9% below ASTM standards, and therefore technically unacceptable for installation. Actual wall thickness dimensions are virtually never checked, however, leaving the mechanical design engineer, pipe installer, building owner, and facility engineers to all mistakenly believe that the stenciled wall thickness dimension or pipe schedule specification is true and accurate.

In this example of 6 in. diameter schedule 40 pipe into a condenser water system where 2 MPY might be expected as a reasonable corrosion rate, the loss of 0.036 in. of material translates into an immediate loss of 18 years of service life.

In a further example, we can demonstrate that undersized pipe is also provide to heavier schedule 80. This section of 3 in. schedule pipe scheduled for installation for steam condensate service which has an ASTM specified wall thickness of 0.300 in. In reality, ultrasonic testing identified a wall thickness of the new pipe, never installed, of 0.266 in.

This is just slightly above the 0.263 in. minimum specified by ASTM, and represents the pipe being undersized to 11.34% of its 12.5% maximum limit. At a typical corrosion rate for steam condensate service of near 1-2 MPY, undersizing this pipe by 0.034 in. means an unnecessary and unanticipated loss of 15 years of service life.

Below, the installation of a new 18 in.condenser water pump header was nearing completion when the ultrasonic investigation at examples of older pipe allowed a quick evaluation to the new pipe still being welded into place. With an ASTM stamp marking the pipe as STD, (standard), as well as a wall thickness dimension of 0.375 in. stenciled on the pipe itself, everyone associated with this piping project likely assumed that 0.375 in. was its true thickness dimension.

Instead, UT testing identified the pipe consistently between 0.332 in. and 0.336 in. across its entire approximate 20 ft. length – remarkably uniform, but lower. At 0.332 in., this new pipe is precisely 12% under its defined ASTM thickness specification; consistent with most new pipe today. Technically, this new 18 in. pipe has a wall thickness more closely associated with 8 in. schedule 40 pipe at 0.322 in.

Ultrasonic testing of the new 12 in. pipe to and from each condenser water pump, again defined by ASTM to have a wall thickness of 0.375 in., instead showed the same low thickness values of near 0.330 in., and again being undersized to near its maximum allowable limit.

In a more common and more critical example immediately left, we measure a new 2 in. schedule 40 threaded pipe nipple having an ASTM A 53 factory wall thickness specification of 0.154 in. However, ultrasonic testing shows a wide variance in wall thickness along its unthreaded center of between 0.134 in. and 0.142 in. – significantly lower that its ASTM specification by 13.6 %, and technically below the ASTM minimum allowable limit for installation.

Similarly undersized 2 in. pipe nipples from the same lot were installed and placed into service – now having only 0.063 in. of usable wall thickness before reaching the outer thread cut and a failure condition.

Unlike larger diameter pipe where a 10 % less thickness dimension might not present any immediate threat, this same loss at small threaded pipe having inherently thinner wall thickness has a significant impact. With 0.072 in. cut away during threading, this unnecessary 0.020 in. loss of material will dramatically reduce service life at all but those systems with the lowest possible corrosion rate.

A recent fire sprinkler investigation even found relatively new ultra thin wall schedule 7 pipe undersized at exactly its 12.5% maximum limitation. With barely any wall thickness available at its formal ASTM thickness specification of 0.093 in. for 3 in pipe, we measured consistent wall thickness values of 0.081 in. – that’s roughly the combined thickness of 2-1/2 standard credit cards. Advanced failure is virtually guaranteed.

• Same Undersized Issue For Copper

A further concern relates to the seemingly similar decrease in quality of copper pipe to steel, as well as its often undersized wall thickness dimensions. In the example of new American made 2-1/2 in. pipe shown at left, a field demonstration of ultrasonic testing procedures to project engineers at a construction job-site revealed dramatically different wall thickness measurements within the same length of new pipe.

With heavier Type K copper tube specified due to a known severe corrosion condition, and having an ASTM defined wall thickness of 0.095 in., our testing identified a wide range in wall thickness from between 0.065 to 0.089 in, and lowest wall thickness a significant 32% below its specification. Measurements were so dramatically low and uneven that observers, as well as the pipe fitters installing the new pipe, questioned the accuracy of the ultrasonic test method.

The pipe was cut and a physical measurement made by standard dial caliper produced the same low wall thickness measurements – with a difference of 0.024 in. at opposite walls. This represents a 25% variance in wall thickness alone; with measurements showing the pipe generally below Type L specifications and approaching thin wall Type M dimensions. A close visual examination, again shown by this photo of the subject pipe with substantially lower wall thickness at left, further supported the original ultrasonic findings. Subsequent dial caliper measurement of the remaining copper pipe stock produced similar results.

For new copper pipe being added to a condenser water system plagued with a high corrosion condition, the design engineer’s intent to extend service life by specifying heavier (and more expensive) Type K copper pipe in reality accomplished nothing. With the service life of all piping being defined by its lowest wall thickness, thin wall Type M copper pipe was instead installed into this project. In the above actual event, the contractor argued that the pipe was acceptable, that the ultrasonic instrument was in error, and the above copper pipe was installed.

• Combined – A Significantly Greater Threat

The supply of undersized pipe is only one of many factors contributing to far lower service life estimates for many different piping systems at newer building properties. Added issues are ineffective or poorly applied and maintained chemical water treatment, the greater use of ERW pipe, poor quality pipe in terms of welding or forming, substantially greater vulnerability to corrosion of today’s pipe products, the impact of foreign pipe products, and poor quality galvanizing.

And the results are dramatic. In contrast to a Rockefeller Center property from 1959 having easily 250+ years of service remaining to its condenser water piping, we have documented the failure of entire condenser water systems requiring their replacement in as few as 4 years; such advanced piping failures always due to a combination of issues and deficiencies. Fire protection, domestic water, sanitary waste – all have the potential for greatly shortened service life.

While each of the above factors still raise debate, and are often difficult to prove to have contributed to a pipe failure to a specific degree, the wall thickness measurement of new pipe prior to acceptance and installation is a very simple, verifiable, and difficult to argue against test that anyone can perform.

You can view and download our two page handout on this subject below.

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