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Know Your Bolts
Posted by MSC on December 3, 2008 at 5:20 PM.

In the past few months, photographs of bolts with what appear to be raw material seams have been circulating on the Internet. These photographs have generated concerns in the industry about what is done or should be done to prevent similar bolts from being used on structural steel construction projects. This has prompted concerns from owners and engineers regarding the quality levels of fasteners manufactured to ASTM standards, particularly overseas.

 

Over the years, and primarily due to the requirements of the Fastener Quality Act, a detailed infrastructure has been developed to assure quality in fasteners. Manufacturers must produce bolts under an acceptable quality management system; ISO 9000 would be an example of such a system. Acceptable quality management systems require many in-process quality control inspections. Manufacturers also conduct quality assurance inspections on a randomly selected sample of the fasteners they produce. These inspections are defined in the individual fastener specifications and include dimensions, hardness, thread fit, wedge tensile, and surface defect inspections. The surface defects shown in the pictures that have brought this issue to the attention of the industry are defined in ASTM F788/F788M. This standard indicates that seams such as those shown in the pictures do have an acceptable limit, but without the supporting results of a comprehensive evaluation, it is impossible to say whether the bolts in the pictures complied with the specification.

 

In the U.S. construction industry, the fasteners may also undergo one of two other tests. In the building industry, the installer conducts Preinstallation Verification Tests on bolts in connections requiring full tensioning. Bolts from each lot are tightened in the tension-measuring device to the minimum required pretension to ensure the bolt assembly and installation method can develop the required clamp load. Additionally, all galvanized structural bolts, as well as all structural bolts used on bridges, are Rotational Capacity Tested. The Preinstallation Verification Test is described in the Research Council on Structural Connections’ Specification for Structural Joints Using A325 or A490 Bolts (2004). There are two versions of the Rotational Capacity Test. One is described in the ASTM A325/A325M standard. The other is in the AASHTO specification.

 

Many years ago there were concerns about fastener quality. In response, quality systems were developed to provide assurance that fasteners were manufactured in compliance with standards. The recent incidents are a good reminder that owners and suppliers should be acquiring fasteners from manufacturers that have implemented acceptable quality systems. This can be done by knowing your supplier and asking about the quality systems their manufacturers use. Suppliers should be able to tell you reasonably quickly whether the manufacturer is certified to ISO or some other recognized quality system. This should be a simple step, and when performed, should be sufficient to verify the quality of the bolts. - Chad Larson, Vice President, LeJeune Bolt Company


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