Ensuring That The Pipe Provided Meets Project Design Specifications
Those involved in the piping industry, from design engineers, to building operators, to steam fitters, are well aware of the changes which have taken place in terms of piping quality over the past few decades. Low price generally rules. Leaving those systems carrying the life blood of a building property often to chance in terms of service life provided.
As we have very well detailed throughout this website, with hard data from 30+ years of involvement in corrosion control and ultrasonic piping investigations, dramatic changes have occurred within the piping industry in terms of pipe source, quality, grade, corrosion resistance, and manufacturing tolerances. Chemical protection and corrosion monitoring varies widely in its effectiveness, or not at all. The movement away from chemical protection and toward “green” technologies, has produced massive pipe damage in just a few years. Changes in piping system engineering design, the use of thinner materials, greater system demands, and changes in materials selection adds further variables to the issue.
Multiple Piping Quality Issues
Most issues are easily addressed and verified by observation, such as piping origin, thickness schedule, or an incomplete longitudinal weld seam. Other issues, such as wall thickness and compliance to American Society of Testing and Materials (ASTM) standards may involve ultrasonic investigation. Pipe quality and corrosion resistance is far more difficult to define; typically requiring samples submission for metallurgical lab analysis.
Major factors addressed throughout this site relating to pipe service life are:
Although high quality foreign pipe products outside the United States certainly exist, building properties constructed since the early 80’s have been plagued by poor quality piping materials from outside sources. Horror stories abound to widespread piping failures in under 5 years.
Although clearly recognized as an issue, and while often excluded by design specification, low quality foreign produced pipe is commonly found installed, and documented as the fundamental cause of pipe failure and service interruption.
While some piping installers have physically removed a stenciled or painted foreign pipe stamp in order to conceal its origin, or turned the stamp away from view, such would seem unnecessary given the volume of clients who act shocked to find that the pipe next to them stenciled “Korea” or “Romania” violated their “USA Only”design specifications.
The great American steel industry was substantially destroyed by excessive environmental controls, labor demands, and competition from low cost foreign imports – an issue which today has resulted in the far greater installation of questionable pipe products.
Most piping systems have reached the limit of what can be tolerated in terms of low wall thickness.
Condenser water and process systems are today specified as standard grade where extra heavy or schedule 80 pipe was once exclusively installed. High pressure steam, once universally supplied by extra heavy pipe, now has been replaced in many applications using schedule 40.
Fire protection systems now use schedule 10 as the standard, with schedule 7 found in a growing number of examples – even where threaded, and where only 0.013 in. of wall thickness will exist at the thread cut. Extra heavy sanitary waste systems are now commonly constructed of ductile iron pipe having half the wall thickness.
Less wall thickness means less service life, and often disproportionately less. In addition, thinner piping materials always corrode to a greater degree than heavier pipe – even within the same piping system and in immediately adjacent locations.
In addition to piping materials and schedules, pipe joining methods have changed in almost every piping service.
Arguments favoring thin wall pipe are obviously cost number one. Less handling weight, lower shipping fees, greater water flow, less welding, faster assembly, and larger inside diameter are also common arguments.
Corrosion Resistance Ratio, CRR, while having nothing whatsoever to do with corrosion resistance or any form of corrosion assessment, does produce a mathematical argument justifying the use of thin wall schedule 10 and schedule 7 pipe.
All pipe of a given size has an outside diameter of the same dimension; with the inside diameter varying according to pipe schedule. Therefore, conformance to design specifications can never be verified by outside measurement. Pipe stamps are accurate and reliable. When missing or incomplete, the source and quality of the product should be immediately suspect.
Substitution to thinner and lower quality piping products, however, does take place more often than suspected. Whether by chance, accident, carelessness, or deliberately planned, the installation of thinner piping materials means less service life and potentially unexpected service interruption.
In the example at left of 12 in. pipe serving a high rise building condenser water system, thinner schedule 20 pipe (0.250 in. wall at right) was randomly substituted where schedule 40 (0.406 in. wall at left) had been specified.
Heavy under deposit cell corrosion, while years away from a threat to the heavier schedule 40 pipe, penetrated through the schedule 20 pipe of 0.156 in. less wall thickness to cause a failure – thereby revealing the material switch 18 years later.
Pinhole pipe failures remained unexplained due to high wall thickness generally present. Further ultrasonic testing identified uniform but dramatically different wall thickness across a welded section. A suspected length of 12 in, diameter riser pipe was removed to show thinner schedule 20 pipe where schedule 40 was specified; offering definitive proof of pipe substitution.
A random deep pitting condition due to deposits settlement at the horizontal lines had produced deep pitting – which reached through the significantly thinner schedule 20 pipe sooner.
We have documented carbon steel pipe installed in the late 1890’s, long before effective chemical treatment ever existed, to be still in excellent condition and capable of providing another 250 years of reliable service.
Wrought iron pipe, still found in older properties, is well known for its corrosion resistance and extended service life, but was removed from manufacture in 1965. Typically providing a corrosion rate for open condenser water service of under 0.4 mils per year, a ½ in. thick extra heavy 18 in. main wrought iron riser from 1945 can easily provide a theoretical service life of over 500 years.
At the same time, we have documented in our ultrasonic failure investigations the complete deterioration of well maintained piping systems in as little as 5 years or less – with new examples frequently added. Properties having renovated or added to existing HVAC systems find their new pipe to fail far in advance of pipe placed in service 50 years earlier.
Although satisfying the ASTM specification for chemical and physical properties, some further elements, either present or absent but still undefined, very clearly contribute to the rate at which that steel pipe will corrode.
Metallurgical testing can offer some insight to the vulnerability of steel pipe to corrosion, with a sample submission to an accelerated salt spray test another valuable predictive tool.
The misapplication of galvanized steel pipe in certain building operating systems means that its premature failure should have been expected. Its advanced failure elsewhere has been attributed to the general deterioration of many galvanized steel piping sources over past decades; similarly to carbon steel. Foreign produced galvanized steel products show unquestionably higher failure rates.
Many fire protection engineers have stopped using galvanized pipe in their fire system designs due to widespread failures known throughout the industry – a reversal of a 20 year growing trend toward galvanized steel pipe previously.
Galvanized pipe for domestic cold water service has been documented to fail in under 10 years and less.
While ASTM standards apply to its manufacture, and the most common hot dip process has not changed in a century or more, such advanced failures strongly indicate that some element to its manufacturing process or in its materials of composition is different now in comparison to decades ago.
Decades ago, nothing but seamless grade steel pipe would be specified for the HVAC piping at any high rise building property piping. Today, the use of ERW or electric resistance welded pipe is common for both carbon steel and galvanized steel piping products. Although regarded as equal, seamed pipe introduces potentially new weakness into any piping system.
The most obvious threat is due to an incomplete longitudinal seam which can occur internally or externally, and holds a greater threat than just the loss of 25% or 75% of its pipe wall.
An internal weld seam deficiency through 40% of its pipe wall is shown at left.
Incomplete internal seams provide the ideal location for iron oxide particulates and microbiological growths to settle to cause accelerated and often severe pitting.
In the worst examples, such pipe may not even survive its hydrostatic test – actually a benefit given that the problem then becomes known rather than reveal itself at a more inopportune time years later.
Differences in composition between the weld filler material and the pipe wall is often identified in metallurgical lab analysis as the basis of greater corrosion activity in that localized area. A straight line measurement of identical wall loss generally defines welded pipe with an incomplete weld seam.
While such physical weld seam defects should be immediately apparent to any experienced steamfitter or pipe installer, the not uncommon identification of such obvious defect suggests that what will not be discovered by the client until years later is often ignored, or at worst – hidden from view.
ASTM defines a wall thickness standard for all pipe of all grades and schedules, in addition to its other physical strength and chemical properties.
In terms of wall thickness, steel pipe is allowed a wide manufacturing tolerance of 25%, or 12.5% plus or minus its ASTM specification. As an example, schedule 40 pipe of 12 in. diameter has an ASTM defined wall thickness of 0.406 in. and an allowable thickness tolerance of between 0.355 in. and 0.457 in., although no concern is necessary when produced over specification.
Contrasting older pipe which can still be found in service 50 years after installation either at or above its ASTM specification, most new steel pipe is produced today at very near its minimum tolerable thickness limit. Schedule 40 pipe isn’t really schedule 40 in most examples, but 12.4% less than schedule 40.
In the example at left, a new section of 3 in. schedule 80 pipe is readied for installation to a steam system, having an ASTM wall thickness specification of 0.300 in.
Instead, ultrasonic testing identifies a consistent wall thickness of 0.266 in. – 11.3% below its ASTM specification.
The impact is far greater at smaller pipe sizes where wall thickness is inherently less, and made further vulnerable since typically threaded.
ASTM does not inspect pipe manufacturers or their products produced. Neither does a UL or FM piping stamp mean that the actual pipe wall thickness is what its written stamp or stencil states.
Ultrasonic testing provides an excellent field assessment tool for ensuring material compliance, although basic visual observation and a caliper are ofthen the only tools needed . Ultrasonic testing is also extremely helpful by documenting existing wall thickness of new piping systems, or pipe condition in a given date, so that accurate comparisons can be made years later. For other questions, such as compliance with a certain ASTM specification, metallurgical lab analysis is the direction to follow.
We provided further information and detail relating to Material Verification elsewhere on the site.