Jun 17, 2011
Hot dip galvanising of fasteners to be reviewedBack
Education|Eskom|Sasol|Africa|Steel|Bob Wilmot|Corrosion Protection
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The current standard practice when hot dip galvanising grades 4.8 and 8.8 fasteners is to apply South African National Standard 121, or SANS 121 (ISO 1461: 2009), specifications and test methods.
SANS 10094 Annex B Edition 4.1 represents the current specification for hot dip galvanising of high-strength components greater than 1 000 MPa, such as grade 10.9 friction grip fasteners.
During 2010, the South African Bureau of Standards (SABS) circulated a Draft South African Standard that will adopt ISO 14399 as a replacement standard for fasteners.
SANS 14399 consists of ten parts for high-strength structural bolt and nut assemblies. The specifications are highly detailed and include greater controls and test procedures.
The effect of the proposed specifications on the hot dip galvanising of high-tensile fasteners, greater than 1 000 MPa, will be the replacement of SANS 10094 with SANS/ISO 10684 titled ‘Fasteners – Hot dip galvanised coatings’.
The current hot dip galvanising cleaning practice involves the pickling of high-strength fasteners in hydrochloric acid. This practice has the remote possibility of causing hydrogen embrittlement of the components.
ISO 10684 allows for both limited acid pickling as well as mechanical cleaning. However, Wilmot says local modifications are being planned to eliminate acid pickling and only allow mechanical cleaning. Implementation of this cleaning process will ensure the total elimination of the potential for hydrogen embrittlement.
Although the standard is still under discussion, Wilmot is confident that the SABS is committed to approving the new specifications, owing to the bureau’s tendency to lean towards adopting ISO specifications and implementing these without modification.
He feels this could have a positive impact on the industry, as it would ensure better quality control, give fastener manufacturers increased responsibility at all levels and extend fastener application.
“Manufacturers will have greater input throughout the entire production process, from checking the quality of the input material to ensuring that galvanising is done according to specification,” Wilmot adds.
Meanwhile, Wilmot tells Engineering News, State-owned power utility Eskom’s build programme to expand its power generation capacity is driving local enquiries about galvanising procedures.
“These are major projects that require not only enormous numbers of fasteners, but also fasteners that have a long life and low life- cycle cost,” he explains.
Following a peak in 2007/8, the industry’s growth fell by between 8% and 10% owing to the economic downturn, after which it stabilised. But growth resumed in the 2009/10 financial year.
“During the last financial year we recorded 4% growth and we are going to conservatively project a further 3% to 4% improvement over the next financial year,” he notes.
However, the total growth of the industry depends on the number of major projects that are on offer.
“Some of our members have been busy with Eskom’s build programme and its associated infrastructure, such as the development of the Grootegeluk colliery. Further, the demand for galvanised fasteners in the mining industry has been fairly static; however, we hope to see growth in the platinum industry that will translate to an increase in demand for fasteners.
“Many platinum projects were put on hold but we believe that the economy has now reached a point where these projects will be resumed. This represents significant growth,” says Wilmot.
Continued growth in the coal-mining industry, not only associated with Eskom, but also with exports and petrochemicals company Sasol, augurs well for future growth.
“The export of commodities, such as coal, platinum and iron-ore, has increased. This has spin-off benefits for the galvanised fastener industry,” he adds.
Wilmot says it is important for engineers and their clients to distinguish and understand the difference between hot dip galvanised and zinc electroplated fasteners.
“Hot dip galvanised fasteners should be referred to as such and not simply as galvanised fasteners, as this could be, and is, confused with zinc electroplated components.
“From a corrosion protection point of view, hot dip galvanised fasteners have much better durability and service life, as the process produces a thicker coating,” he adds.
Hot dip galvanising coating thicknesses normally range between 60 µm and 70 µm, whereas zinc electroplating thicknesses are between 6 µm and 10 µm.
“It sometimes appears that fasteners, which are in reality a highly technically important piece of equipment, do not receive the attention they deserve. Damage or shortages in supplies tend to be caused by end-users visiting the nearest hardware shop to purchase readily available fasteners, which, in most cases, consist of zinc electroplated fasteners,” he says.
“In general, what we advocate is for engineers to consider the life cycle costing for construction materials, including the appropriate corrosion control specification of fasteners, when projects are designed,” Wilmot adds.
Further, incorrect application owing to a lack of skills and training of construction personnel is another challenge with costly consequences.
“Installation of fasteners must be done correctly to ensure maximum product life and efficiency. Site assembly crews that are responsible for installation of structural steel must be educated to appreciate the importance of specified fastener assembly procedures. It often appears that end-users tend to treat fasteners as unsophisticated equipment; however, quite the opposite is true,” he explains.
“We believe that, through proper education and creating an understanding of hot dip galvanised products, end-users will appreciate and apply such components on appropriate projects.
Associated with this is motivating our hot dip galvanising members to produce high-quality products,” he concludes.
Edited by: Chanel de Bruyn© Reuse this Comment Guidelines
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