Photo Gallery C5:  Favorable Pipe Conditions Fortunately, not all ultrasonic investigation produce the type of results indicated by our Photo Galleries.  In fact, many of our UT reports are excellent, and help to assure the building owner of long and reliable pipe service.  All pipe is expected to show some impact due to the unstoppable forces of corrosion.  These may be countered by the natural corrosion resistance of the pipe, such as brass or TP, through the addition of a protective finish such as galvanizing, and / or through the addition of corrosion control chemicals.  When accessible to internal inspection, the absence of internal rust or other deposits, surface pitting, and the observation of a relatively smooth internal pipe wall is an always welcomed finding. For most investigations, results range somewhat midpoint.  In many examples, a thread leak prompting an investigation will expose the fact that threaded schedule 40 pipe only provides a finite number of years of service and has reached retirement, yet all larger welded pipe still offering another 50 years of reliability.  External corrosion due to lack maintenance at the cooling tower pipe does not necessarily define the need for an entirely new piping system. For one…

Photo Gallery C4:  Cut Grooved Pipe Grooved clamped pipe has a long history of providing outstanding service.  Nevertheless, certain issues exist for any environment where corrosion is a concern. One of the greatest threats to any grooved piping system is where the groove is cut into the outside of the pipe rather than rolled.  When rolled, the pipe wall is pressed or swaged into the outer wall resulting in that pipe wall material being forced inward to created a very noticeable raised bump.  Technically, no pipe wall is lost.  When cut, the same depth of the groove is physically removed from outer pipe wall to leave the pipe thinner in this localized area.  The impact is similar to threaded smaller diameter pipe. Cutting the groove then introduces an immediate vulnerability to each end of any smaller diameter pipe since corrosion no longer needs to penetrate the full pipe wall, but to only reach the base of the cut groove.  A small leak, should it occur, then initiates a second corrosion front within the outer groove surface and to the clamp as well.  If cut unevenly, the physical strength and reliability of the fitting is reduced. Cut grooved pipe has certain…

Photo Gallery C3:  ERW Seamed Pipe Up until about 25 years ago, ASTM A53 seamless pipe was the only material recommended or specified for any HVAC system.  This was due to the greater vulnerability of the weld seam through either incomplete welding, issues with the filler material, or its lifetime greater susceptibility to various forms of corrosion.  Since then, lower cost ERW pipe has taken over the market, having first been accepted throughout the fire protection industry. The higher incidence of failures at ERW weld seams clearly documents the problem to still exist, although from our experience, it seems more prevalent at foreign produced pipe.  One clear benefit of US produced steel pipe is its superior ERW weld quality, with other issues of undersized pipe and higher corrosion susceptibility remaining equal to foreign products. The identification of  defective ERW weld seam is often made visually by measuring a straight line of pinhole failures, but can also be determined using ultrasonic testing.  An external cut or groove down the entire length of pipe is another reliable clue.  A defective groove, more common to find internally, is not visible once the pipe is assembled.  Although ASTM has strict specifications relating to ERW…

Photo Gallery C2:  Foreign Pipe Stamps The early introductions of steel pipe from China and Korea into the American market in the early 1980s was met with severe opposition by most piping steamfitters due to its generally lower quality, difficulty in cutting, welding and threading, and a greater rate of failure during hydraulic pressure tests.  With the building industry’s movement from seamless pipe to lower cost ERW seamed pipe, the failure of foreign ERW pipe seams was a common issue beyond just lower quality.  This resulted in a prohibition of foreign pipe by many piping design engineers and a “domestic only pipe” clause in many piping specifications regarding the source of the pipe provided.  That prohibition still remains in effect for most federal and state building projects. Later, such restrictions were relaxed, although not due to any improvement in foreign pipe quality.  While some prohibitions still remained, the larger the project and the greater the savings provided by low cost foreign pipe products, the greater the probability of finding them installed years later.  Many prohibitions were no more than a wink and a nod: discussions regarding the lower quality of foreign pipe and its threat to the project conducted in…

Photo Gallery C1:  Undersized New Steel Pipe Most professionals associated with the design and construction of any building or piping system has likely assumed that the pipe wall thickness specified for different products equals what is defined by ASTM.  An ASTM, UL or FM stamp at a section of 12 in. schedule 40 pipe ready for installation means that the pipe wall is as defined by the stamp at 0.406 in.  Right? Well not really.  Just like the incredible shrinking bag of potato chips, crackers, or cereal box, pipe manufacturers seem to have followed a similar path. It begins with the fact that pipe can be produced +/- 12.5 % of its ASTM defined wall thickness and still be termed acceptable for sale and installation; a 25% tolerance which was appropriate in the early 1900’s when the code was first written and steel pipe manufacturing was in its infancy, but not today over 100 years later.  Clearly American pipe manufacturing has improved in the past 100+ years! Prior to three or more decades ago, almost all pipe was manufactured at or above true ASTM specifications, and in fact it is not unusual to still document pipe at older at well…

Photo Gallery B8:  Steel to Steel Electrolysis Electrolysis can occur at steel pipe which is supported by structural steel depending upon the difference between its ground potential and the ground potential of the building itself.  This is a relatively rare event which typically occurs hidden from view at the contact surface of only one metal side.  A different but more common issue occurs when copper pipe is support by a steel pipe hanger. It is most common for pipe where its outer surface is wet for any reason, given that the surface moisture then becomes an electrolyte favoring the movement of electrons.  For outdoor located pipe supported by either pedestal or pipe hanger, water and weathering may also play a role; accelerating the localized loss. Steel to steel electrolysis has been identified in the immediate vicinity of the pipe hangers of fire sprinkler systems and where condenser water lines are supported by floor mounted pedestals or pipe hangers from some other building grounded support, such as the cooling tower.  Although different types of plastic or different electrical isolators exist, they are rarely if ever installed for HVAC applications.  Improper grounding is a common source of the…

Photo Gallery B10:   Brass Dezincification Dezincification is more of a chemical transformation than a corrosion event.  It occurs to brass pipe after a long period of service, typically at or about 80 years, and is greatly dependent upon the type of brass pipe installed in combination with the composition and aggressiveness of the local water supply.  The problem arises from the natural affinity of water for zinc, a chemical element from which brass pipe is made.  Red brass has a lower percentage of zinc and is far less impacted by dezincification, whereas more commonly used yellow brass has a much higher percentage of zinc and therefore is far more vulnerable. Common signs of dezincification are round chalk like deposits on the pipe surface, which represent areas where the zinc has been leached out or been removed to produce a more porous form of copper.  If removed or cut open for visual inspection, similar chalk like deposits are also viewed inside.  Where no such markings are present, a metallurgical lab analysis is required to identify the condition.  As certain photos in our gallery illustrate, removing the external deposits produces a condition where the brass pipe has seemingly…

Photo Gallery B6:  Weathering Of the various forms of corrosion common to any building property, external pipe corrosion caused by weathering, cooling tower overspray, and outdoor environmental conditions is the easiest to avoid.  For uninsulated steel pipe, corrosion is immediately apparent beginning with the first blemish, and can usually be stopped long before it develops into a larger problem.  Virtually all such conditions are entirely due to a lack of maintenance over a very extended period of time. Common problem areas are at pipe supports and hangers where water collects, and at the flanges of vertical pipe sections where water will pool.  Insulated pipe is far more likely to conceal a corrosion problem than prevent one.  Ironically, insulating the pipe to protect it from external corrosion often produces the opposite effect given that it allows a severe corrosion condition to develop hidden from view.  An active 24 in. condenser water system operating 24/7 will never freeze under most winter conditions.  Once insulated, however, the external corrosion threat is presumed to have been eliminated, when in fact insulating the pipe has only guaranteed a future problem. Most outdoor insulation is inadequate for its purpose, too thin, and…

Photo Gallery B9:  Microbiologically Influenced Corrosion Microbiologically Influenced Corrosion, commonly termed MIC, can produce excessive corrosion losses of up to 50 MPY and greater, but fortunately it is relatively rare.  Microbiological corrosion is associated with heavily contaminated open condenser water systems where large volumes of rust and debris have settled.  It has also been cited as the cause of premature failure and the blockage of dry and pre-action fire sprinkler systems, although mistaken as such in most cases we have investigated. The severe corrosion loss caused by MIC is related to the fact certain anaerobic microorganism, classed as sulfur reducing bacteria (SRB), produce highly acidic conditions which in effect dissolve away the steel pipe.  Trapped under rust and other particulate deposits, such microorganisms mutate to become anerobic, meaning that they no longer require oxygen.  Instead, they draw energy from the steel substrate; producing severe wall losses as a result.  Confirmation of an MIC condition is extremely important in order to plan for the correct response, with laboratory confirmation is required.  Field testing kits for MIC are available but require very specialized live sampling methods. Severe cases of MIC are extremely difficult to eradicate, and the deep…

While various initiating conditions exist, under deposit corrosion is primarily due to the settlement of rust deposits at by-pass, dead end, futures, full flow headers, crossover connections, or wherever low flow conditions favor rust and debris deposition.  The issue is very common to open condenser water systems where naturally higher corrosion levels are added to by captured airborne particulates.  The problem can also be the result of microbiologically influenced corrosion activity known as MIC – a closely related subject. A telltale indication of under deposit corrosion is the identification of tuberculation nodules visually, or the measurement of random low wall thickness ultrasonically.  In both examples, the depth of penetration into the steel pipe is directly proportional to the volume of rust deposits above. Although most large diameter piping systems can easily handle a 5 MPY wall loss, it is the volume of rust produced and its settlement which then elevate pitting to 35 MPY levels.  Under deposit corrosion is generally random.  Very quickly, and without aggressive actions, it will doom the piping system affected.