Lamellar Tearing and Failures Cases
Seth M. Moyer, BAE/MAE, The Pennsylvania State University, 2012

Keywords: lamellar tearing, steel plates, cracking, welding, metallurgy, material deficiency, brittle fracture, hydrogen, El Paso, Grand Coulee, Atlantic Richfield, King Street, through-thickness, heat-affected zone, rolled steel

Introduction

Lamellar tearing is a material deficiency that can lead to brittle fracture in particular types of structural steel element assemblies. It is characterized by the cracking that can occur in vulnerable steel members beneath the weld, especially in rolled plates, due to low through-thickness ductility and localized strains. Separation in the base material is due to shrinkage strains induced by the cooling of the weld material and high non-metallic inclusion contents in the member. The low ductility is a direct result of the rolling process of plates and members perpendicular to the direction of rolling. Several high profile case studies of projects impacted by lamellar tearing failures will be discussed, including the El Paso Civic Center in Texas, the Grand Coulee Transmission-Line Towers in Colorado, the Atlantic Richfield Towers in Los Angeles (see Figure 1) and the King Street Bridge in Melbourne, Australia.

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Figure 1: Twin 52-Story Atlantic Richfield Towers (Photo Credit: Minnaert via Wikimedia Commons)

Overview

Lamellar tearing describes the cracking that occurs beneath the weld in what can be characterized as a brittle failure of steel in the dimension perpendicular to the plane of rolling. This sort of tearing, which first manifests as microscopic cracks in the base metal (most often internal), typically occurs in steel at heavily restrained welded joints where the thickness of the plate exceeds 1 1/2 inches (Kaminetzky 1991, p. 243). Heavy internal restraint provides little leeway for the expansion and, more specifically, the contraction that susceptible steel elements undergo during the cooling of the weld. Thus, the steel rips in the through-thickness direction due to the localized shrinkage strains and low ductility.

Tearing occurrs parallel to the surface of the plate, inside of or, more commonly, adjacent to the outer edge of the heat-affected zone (HAZ), usually within about 5 mm of the weld face (Ross 1984, p. 265). The tears typically have a stepped pattern made up of prominent horizontal terraces connected by vertical or diagnonal portions (ASTM 2003, p. 4). Figure 2 below shows the typical tearing pattern beneath the weld in a steel plate. The following sketch was based on "Figure 1: Lamellar Tearing in T Butt Weld," from the European Federation for Welding, Joining and Cutting Technical Sheet on "Lamellar Tearing" (http://www.ewf.be/media/documentosDocs/doc_78_lamellar_tearing.pdf) and "Figure 10: Lamellar Tearing," from the ESDEP Course Notes, "WG 2: Applied Metallurgy, Lecture 2.6: Weldability of Structural Steels," from the University of Ljubljana Faculty of Civil and Geodetic Engineering (http://www.fgg.uni-lj.si/kmk/esdep/master/wg02/l0600.htm).

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Figure 2: Shrinkage Strains Cause Tearing Outside of the HAZ (Image Credit: Seth Moyer)

Research conducted in the early 1970s found that lamellar tearing was influenced by a number of factors including contraction stresses, the presence of non-metallic inclusions and hydrogen diffused from the weld material into the surrounding steel. It was concluded that inclusion content was the major factor to be eliminated in order to control lamellar tearing. With the introduction of low sulfur steel in the early to mid-1970s, widespread lamellar tearing was all but eliminated. These "clean" steels have sulfur levels below 0.005% (Still 2004). Construction projects before the mid-1970s used commercially produced steel in which sulfur levels could be as high as 0.04% (Still 1995, p. 447). However, hydrogen diffusion, as an inherent result of the welding process, can not realistically be eliminated altogether.

Causes

Step-like tears typically originate from elongated non-metallic inclusions inherent in the steel. Shrinkage strains cause the inclusions to shatter or decohere from the adjacent steel material, which creates a void and triggers tearing. The rolling process creates concentrated laminations of inclusion materials parallel to the top and bottom plate surfaces, producing localized regions of low ductility. Because of this effect of rolling steel, levels of non-metallic inclusions must be reduced in order to improve ductility perpendicular to the plane of rolling (ASTM 2003, p. 4).

Hydrogen-induced cracking in the heat-affected zone (HAZ) of the base or parent metal is another leading factor responsible for occurrences of lamellar tearing in modern steel construction. Research has indicated that the method of welding has the greatest influence on whether or not an element will be vulnerable to lamellar tearing (Ross 1984, p. 265). A major source of hydrogen during the welding process is the moisture that is contained within the electrode coating itself. Other sources of hydrogen in the weld material include moisture in the flux, hydrogenous compounds in the coating and/or flux and dirt, oil, grease and rust on the welding wires. For the weld base material, hydrogen sources include surface dirt, oil, grease and rust, degreasing fluids for cleaning the surface to be welded and hydrogen in the parent steel. Ambient atmosphere moisture can also be a minor source of hydrogen (Bailey 197, pp. 5-6).

Hydrogen is absorbed into the weld bead from the arc atmosphere during application of the weld. A lot of this hydrogen diffuses out of the solidified weld and some that escapes diffuses into the base metal (Bailey 1973, p. 5). The diffused hydrogen acts in a similar manner to its behavior in a sour (H2S) environment. In a sour environment, hydrogen sulfide dissociates into atomic hydrogen and works into the weld and base materials. The hydrogen atoms reform into molecular hydrogen when they cross non-metallic inclusions. This process can eventually cause a buildup of the molecular hydrogen which builds pressure within the inclusion. This internal pressure forms where the shrinkage stresses have also concentrated at the individual laminations that result from material impurities, eventually leading to tearing (Still 2004).

Prevention

It is very important for structural designers to realize that differences in steel strength exist. Structural steel is not as overall homogeneous of a material as many once believed (Kaminetzky 1991, pp. 243-44). While it is now commonly understood that steel is weakest in the direction perpendicular to rolling, relatively little is known about the properties of steel in its through-thickness (z-axis) direction compared to the longitudinal and transverse directions. More than two decades after lamellar tearing was first recognized in the early 1960s, there were still no methods developed for testing the through-thickness properties of steel (Ross 1984, p. 257).

In 1986, the American Society for Testing and Materials (ASTM) first released a standard specification for through-thickness tension testing of steel plate elements. The ASTM A770 standard specifies the procedure and acceptable results for determining the reduction in cross sectional area of a specimen through the application of a tensile test in the direction perpendicular to the plane of rolling. ASTM A770 can be used to quantify a measure of resistance to lamellar tearing in steel plates greater than or equal to 1 inch in thickness. According to the standards for acceptable ductility, test specimens should have a minimum reduction of area equal to 20%. Some common steel-making processes which offer improved z-axis ductility include low sulfur practices, inclusion shape control, electroslag or vacuum arc remelting and vacuum degassing (ASTM 2003, pp. 1-2, 4).

One of the simplest and most effective ways to avoid susceptibility to lamellar tearing is through the specification of proper connection detailing. Where possible, plates should be organized so that the through-thickness direction is used minimally. Figure 3 below shows several vulnerable and improved welding details to reduce the risk of tearing failures where potentially susceptible welding configurations are necessary.

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Figure 3: Susceptible and Improved Details (Image Credit: American Institute of Steel Construction)

Welding inspections, in addition to the basic visual inspection that the fabricator/erector is responsible for, must be specified by the designer where he/she sees fit. Visual inspection is the most common and economical method for checking welds. This method is typically sufficient for quality control of welds and if an issue is detected, it can then be repaired or further inspected via other tests. In penetrant testing, red dye is applied to and penetrates the crack. The excess dye is removed and white developer is applied to the surface. Any dye that has made its way into a crack seeps out and can be seen clearly on the developer (Steel 2011, p. 8.4).

Visual and penetrant testing work only to detect surface cracks. Magnetic-particle testing uses a magnitizing current in the welded connection to create a magnetic field within the element. Cracks and inclusions interrupt the field and the dry magnetic powder dusting applied to the surface gathers at the interruptions. This method can indicate surface cracks (which may have been too tight/small for dye to enter in penetrant testing) as well as internal cracks within 0.1 inches of the surface. Ultrasonic, or sonar, testing uses a technique called pulse echo in which a high-frequency sound is sent into the metal via a crystal, which then receives the reflections from the other end of the member and any voids/cracks that may be present. Ultrasonic testing has a broader application and is both quicker and more economical than radiography, but its accuracy and the reporting of any discontinuities found is largely reliant on the operator. Radiographic testing works as an X-ray film process, producing a permanent record of its findings with an X-ray negative. For a crack or void to be detected by this method, it must be nearly parallel to the radiation beam and must occupy around 1 1/2% of the thickness of the element. Radiography is the most expensive method of weld inspection. Because of the costs and precautions necessary when dealing with radiation, ultrasonic methods have become the go-to test for detecting internal discontinuities (Steel 2011, pp. 8.5-8.7).

If issues are detected in a welded connection, reparative measures should be carried out. Researchers at Lehigh University recommended cutting out and replacing the heat-affected area in the base metal or using the "buttering" technique in which the weld material is built up with multiple layers, providing greater ductility to respond to the shrinkage strains of the cooling weld. The researchers also reported that in some cases, preheating the steel to be welded decreased the likelihood of lamellar tearing. Peening of the steel also helped to improve tearing resistance by relieving some of the tensile stresses and strains in the plate material (Ross 1984, p. 266).

Failures Cases

Fortunately, in the cases that will be discussed here, the material failures that occurred resulted in purely financial losses with no loss of life. However, if lamellar tearing problems are not corrected in a structure in which brittle fracture of the steel becomes imminent, the results could be catastrophic in the event of an earthquake (Ross 1984, p. 256). These building material failures led to both heavy expenses and lengthy schedule delays when large scale connection testing and repairs had to be undertaken.

El Paso Civic Center

During construction of the civic center theater of El Paso, Texas in 1972, hidden cracks developed in the welded joints of the roof compression ring (Ross 1984, p. 256). The 138-foot-diameter compression ring consisted of a 2' x 4.6' box girder and was located between the two intersecting crescents making up the theater (Concrete 1974). The girder was originally designed as twenty-five separate sections joined together with heavy, full-penetration welds connecting the flange plates, which ranged from 2 1/2 to 3 inches thick, to the 1 inch diaphragm plates. However, the design was changed to use fillet welds along the top and bottom of the ring girder. The use of these fillet welds, in turn, eliminated the full-penetration welds that were to be used in the side plates of the girder (Kaminetzky 1991, p. 244). The altered welding configuration created joints in which the flange plates were particularly susceptible to lamellar tearing.

In Figure 4 below, the sketch is showing an enlarged plan view of the 4.6' wide box girder, looking down at a joint joining two sections of the ring at a diaphragm plate. The diaphragm plate is shown extending beyond the flange plates and the fillet welds joining the diaphragm and flange plates are depicted with dark shading. The steel tears appeared beneath the fillet welds in the heavy flange plates. Figure 5 shows the repairs that were made at the girder connection joints. Part of the diaphragm plate and portions of the flange plates affected by the original fillet welds have been cut out and replaced with weld material fill, depicted with gray shading. Both of the following sketches were based on the photos of "Figure 6-4" on page 259 of Construction Disasters: Design Failures, Causes, and Prevention by Steven S. Ross.

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Figure 4: Lamellar Tearing Beneath the Fillet Welds in the Flange Plates (Image Credit: Seth Moyer)

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Figure 5: Diaphragm and Damaged Flange Plate Material has been Removed and Replaced with Weld Material (Image Credit: Seth Moyer)

The civic center was originally estimated to cost $5 million and was expected to be completed by March 1973. After discovery of the steel tears, El Paso's public works department had all of the welded joints in the cable roof compression girder inspected ultrasonically at a cost of $150,000. Robert E. McKee, Inc., the general contractor, also spent nearly $150,000 on additional quality control measures. In March 1975, with the project two years overdue, McKee sued the city of El Paso for $2.3 million. A total of sixteen subcontractors as well as the architects were also sued. In response to the initial suit, the city of El Paso filed against the structural engineer, the steel supplier and the American Institute of Steel Construction (AISC) for the $2.3 million and another $247,603 (Ross 1984, pp. 260, 264).

With just two weeks until the start of the trial in February 1980, the dispute was settled with all parties sharing the blame. Almost every party involved agreed to pay into a combined $1 million which went to McKee. A portion of that sum was also distributed to the subcontractors. The amounts of the individual payments were all at least $100,000 and were contributed by the city of El Paso, the AISC, Armco Steel Corp. (steel supplier), architects Garland & Hilles, Carroll, Daeuble, DuSang & Rand and Barnard Mulville and structural engineers A. B. Peinado & Son, Inc. and Severud-Perrone-Sturm-Bandel. In addition, some of the subcontractors withdrew or decreased the amount of their individual claims (Ross 1984, pp. 264-65).

Grand Coulee Transmission-Line Towers

Near the summer of 1973, the U.S. Bureau of Reclamation was forced to halt the construction of twenty power transmission-line towers at their Third Powerplant, located at the Grand Coulee Dam in Colorado (see Figure 6), due to lamellar tearing. At the time, only one tower had been erected and needed to be taken down. However, twelve of the other towers also experienced cracking in their welded steel frames (Ross 1984, p. 260). The cracking was not thought to be all that significant originally until magnetic-particle testing showed that the cracking was much more severe. These findings resulted in a total redesign of all towers and the costly deconstruction of the towers that had already been built (Kaminetzky 1991, p. 244).

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Figure 6: Aerial View of the Grand Coulee Dam (Photo Credit: Wikimedia Commons)

The towers were designed with welded tubular steel columns and rectangular crossarms. Where the tapered steel crossarms connected to the columns, a rectangular box girder tied the columns to one another. The lamellar tearing originated in the diaphragm plates which extended through the cross section of the box girders and between each of the tubular columns (Ross 1984, p. 260). Engineering News Record reported that the lamellar tearing issues were unexpected and all the more shocking since the plates ranged in thickness from 3/8 to 1 1/16 inches. These plates were significantly thinner than the 1 1/2 inches and heavier sections that are typically associated with tearing susceptibility. Prior to this, tearing had not been recognized in plates so thin. The arrangement of the joints in the towers led to very heavily restrained conditions, eventually initiating the cracks (Kaminetzky 1991, p. 244).

In the redesign of the transmission towers, the connections were configured in a way that the plates were no longer running through the cross section of the box girders. The original towers, which were designed in 1970, cost the U.S. Bureau of Reclamation $950,000 and another $952,000 was spent to reconstruct them in accordance with the new specifications (Ross 1984, p. 260).

Atlantic Richfield Towers

The 52-story twin towers in Los Angeles, California (see Figure 1) tallied $400,000 worth of repairs due, partly, to the effects of lamellar tearing (Ross 1984, p. 256). Delayed cracks were detected at the column spandrel connections and nearly ten percent of the spandrel/beam flange connections were damaged. The cracks developed in the plate base metal as well as within the welds themselves. Both the column and spandrel members that experienced material failures were made up of very heavy elements, all 1 1/2 inches or thicker. However, lamellar tearing was not the only kind of cracking failure that occurred in the steel members. In an extremely unusual manner, the ASTM A-36 mild steel that was used in the fabrication of the column and spandrel members behaved in a brittle, rather than ductile, way (Kaminetzky 1991, p. 244).

King Street Bridge


The all-welded steel girder King Street Bridge experienced similar brittle behavior to that of the Atlantic Richfield Towers in its BS 968 (British Steel Specification) members. The bridge, which spanned the Yarra River in Melbourne, Australia, collapsed on July 10, 1962, when its four girders failed due to brittle fracturing. The high tensile strength steel had a high carbon content, which led to lamellar tearing and overall weakness in and around the heat-affected zone. The low temperatures (down to 14 degrees F) exacerbated the brittle behavior and allowed for crack propagation once stresses had been concentrated at non-metallic inclusions and tearing was initiated. In the end, the high carbon steel (not appropriate for welding in this capacity), poor detailing and low temperatures combined to cause the failure of the bridge (Bridge 2011).

For more on the King Street Bridge collapse, visit the MatDL case study page here: http://matdl.org/failurecases/Bridge_Collapse_Cases/King_Street_Bridge.

Conclusion

With the advent of "clean" and accessible commercially produced steels in the early to mid-1970s, lamellar tearing due to non-metallic inclusions was virtually eliminated through significantly reduced sulfur levels. However, material impurities are always inherently characteristic of any structural steel member's compostion. The often microscopic internal laminations in the steel that result from these inclusions provide a point for stress concentration and overall member weakness. Considering these impurities along with the effects that hydrogen has in the welding process when moisture is present, hydrogen-induced cracking and lamellar tearing in and around the heat-affected zone of the parent material remain a serious area of concern when designing those types of highly restrained welded connections that are susceptible to this brittle material failure.

In closing, when avoiding welded joints configured in such a way that through-thickness shrinkage strains will be induced in thick, rolled steel elements is not possible, engineers and designers should take into consideration the following recommendations to protect against lamellar tearing material failures when detailing/specifying welded joints:
  • For critical joint members, have the base metal checked for the extent and locations of laminations ultrasonically
  • When dealing with existing steel members, determine if sulfur levels are excessive (>0.005%)
  • Specify preheating of the base metal according to established welding processes
  • Specify the use of vacuum packed electrodes for welding of susceptible joints
  • Keep electrodes in the original manufacturer's packaging until ready to be used
  • Old or surplus electrodes which are rebaked must not be utilized in joints where lamellar tearing is a concern
  • Preheating and welding temperatures must be carefully monitored (Still 1995, p.448)
  • Specify welds with the minimum throat dimension required to resist applied loading
  • Select electrodes which will produce a weld with the lowest yield strength necessary for the connection, as high weld yield strengths could induce strains in members above their yield strengths
  • When possible, weld subassemblies together separately before completing final assembly
  • Carefully investigate the potential restraints that will be present after the overall assembly is completed when utilizing prequalified joints
  • Limit the number of tack welds used and their size
  • Do not specify stiffening elements unless absolutely required, as they induce heavy restraint
  • Where required, limit stiffeners and their welds to the minimum sizes required
  • Selectively specify ultrasonic inspection of welds and affected base metal after critical heavily restrained joints have been fabricated/assembled (Ross 1984, pp. 263-64)

Bibliography

ASTM A770/A770M - 03. (2003). Standard Specification for Through-Thickness Tension Testing of Steel Plates for Special Applications. ASTM International. pp. 1-2, 4.
This is the standard specification for through-thickness tension testing of steel plate elements published by the American Society for Testing and Materials.

Bailey, N. (1973). Welding Steels without Hydrogen Cracking. 2nd Ed. Cambridge, England: Abington Pub. pp. 5-6.
This book covers, in detail, hydrogen cracking, which is the most common problem in welding steel structures..

"Bridge Collapse Cases/King Street Bridge." (September 5, 2011). MatDL: Failure Cases Wiki. <http://matdl.org/failurecases/Bridge_Collapse_Cases/King_Street_Bridge> (December 18, 2012).
This page of the failure case studies site provides an overview of the King Street Bridge collapse in Melbourne, Australia.

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Concrete Construction Staff. (April 1, 1974). "A Problem in Structural Steel." Concrete Construction. <http://www.concreteconstruction.net/structural-steel/a-problem-in-structural-steel.aspx> (October 4, 2012).
A brief article about the issue of lamellar tearing and its construction and cost impacts on both the El Paso Civic Center and the Atlantic Richfield Towers.

Kaminetzky, Dov. (1991). Design and Construction Failures: Lessons from Forensic Investigations. New York: McGraw-Hill. pp. 243-44.
This book provides a brief overview of lamellar tearing and offers details about the failures that occurred at the El Paso Civic Center, the Atlantic Richfield Towers and the Grand Coulee Towers.

"Lamellar Tearing." (2007). Technical Sheets, European Federation for Welding, Joining and Cutting. <http://www.ewf.be/media/documentosDocs/doc_78_lamellar_tearing.pdf> (October 4, 2012).
This technical sheet provides information on the location, appearance, causes and risk reduction factors of lamellar tearing in a straightforward format.

Ross, Steven S. (1984). Construction Disasters: Design Failures, Causes, and Prevention. New York: McGraw-Hill. pp. 255-66.
This book provides an informative look into the timeline and details of the El Paso Civic Center, the Grand Coulee Towers and the Atlantic Richfield Towers lamellar tearing failure cases and the response to them.

Steel Construction Manual. (2011). 14th Ed. Chicago: American Institute of Steel Construction. pp. 8.4-8.7, 8.22.
This book is a steel construction design and reference manual and includes the 2010 AISC Specification for Structural Steel Buildings.

Still, J. R. (January 2004). "Understanding Hydrogen Failures of Ferritic Welds." Welding Journal, American Welding Society, Vol. 83, No. 1, pp. 26-29.
This article addresses how to reduce the effects of hydrogen-induced cracking and corrosion as well as the common failures associated with hydrogen, including lamellar tearing. It can be found in electronic format here: http://www.aws.org/wj/jan04/still_feature.html.

Still, J. R. (November-December 1995). "Lamellar Tearing - A Ghost from the Past." Welding and Metal Fabrication, Vol. 63, No. 10, pp. 445-48.
This article covers the causes of the tearing that is common with steel used in the 1970s while outlining various tests used to assess the likelihood of material failure.

Additional Resources and References

Verdeja, J. I., Asensio, J. and Pero-Sanz, J. A. (January 2003). "Texture, Formability, Lamellar Tearing and HIC Susceptibility of Ferritic and Low-Carbon HSLA Steels." Materials Characterization, Vol. 50, No. 1, pp. 81-86.
Presented in this article is the influence of the texture and grain orientation of ferritic and low-carbon steels on the mechanical material properties, such as ductility and toughness.

"Welding Technology for Canada: Commentary on Lamellar Tearing." (June 1996). Welding Canada, Welding Institute, Insert 1-4.
This article describes the details of the lamellar tearing mechanism and outlines design avoidance and inspection methods.