British Association of Reinforcement
It's all built in. Reinforced concrete provides essential security.

January 26, 2015

BAR Guidance Note: Boron

The British Association of Reinforcement (BAR) has been alerted to the fact that some of the reinforcement imports entering the UK market have contained boron (see note below).  Boron is not specifically referred to in BS4449 as it is not normally added to reinforcement bar, but even small additions of boron can dramatically affect the hardenability of a steel and hence its welding characteristics, leading to quality and potential safety issues. It is reported that some Chinese mills have previously added boron for a commercial export rebate.

 The effect of boron on the hardenability of steels is a well documented phenomenon and it is specifically added to some engineering grades of steel to take account of this aspect, but not steel reinforcement. BAR is not aware of any detrimental effect of boron on the mechanical properties of reinforcement bar as traditional cut and bent.

 However, for some welding processes the boron can significantly increase the hardness of the weld area thereby making it much more susceptible to cracking. Often this cracking does not occur until 24-72 hours after welding, the defect is sometimes called delayed-cracking, so if the cracks develop after delivery and these welds are used as lifting points then there is a potential safety issue.

 TWI Limited has advised that, in combination with the other elements in steel boron levels above 5ppm (parts per million) can increase the risk of cracking.  As such, additional precautions, such as slower welding, higher heat input and additional controls on consumable hydrogen levels should be taken when welding boron-containing material.  It is recommended that a specific weld procedure is developed for welding the boron containing steel, if the existing weld procedures have not been qualified on boron-containing material.  For guidance on weld procedure development contact TWI at www.twi-global.com

 As boron is not mentioned in BS4449 its presence will not normally be displayed on the suppliers test certificate, so it is recommended that your reinforcement supplier is contacted or get a sample tested yourself.  BAR has been invited by the BSi committee to provide details to the design committee for consideration whilst UK Steel is to draft an amendment to BS4449 to ensure that steel producers declare intentional additional additions of micro alloys and alloys during the audit process.

 ends

 Notes

The test samples came from CELSA UK's routine testing of competitor materials supplied in the UK market. They were tested in CELSA UK's laboratory. CELSA UK will continue to offer their services to anyone who has concerns about the analysis, physical or mechanical properties of materials. For copies of the test results contact Steve Elliott, BAR Chairman, email: [email protected]

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