The Risk Of Hydrogen Embrittlement of 10.9 and 12.9 Grade Hot-Dip Galvanized Bolts BECOMES A THING OF THE PAST

 

Cleaning of the fasteners such as bolts, nuts, studs from dirt, rust, and scales during the zinc plating process,  is usually done by immersing into the acid baths prior to galvanization. During this cleaning; The hydrogen molecule (h2), released by the reaction of iron (Fe) and hydrochloric acid (HCl), leads to a steel disease called Hydrogen Fragility or Hydrogen Embrittlement by entering the structure of bolts, nuts, and studs of high strength, hardened carbon steel group within a few minutes. As a result of this disease, sometimes the bolts and nuts may break easily, bolted connections may collapse, and material and moral damages may occur in the facilities or vehicles. This risk of fragility can be partially avoided in electro-galvanized steel by heating the bolts for 4 hours minimum, 5 to 8 hours at a temperature of 200˚C,immediately after the coating. Although this process is applied on 12.9-grade bolts, it cannot be said that Hydrogen is 100% removed from the structure.

 

 

Before answering this, must be noted that bolts, nuts and studs are divided into two groups as low and high strength:

As is known, bolt, nuts, and studs produced from the steel bar or coil materials using the methods of either hot or cold-heading or turning and used without any hardening, called as low strength fasteners, the bolts, nuts, and studs produced in a similar way from the more expensive and quality-alloy materials with the increased strength of 50 to 100% by hardening in a suitable oven with protective gas, are called as high-strength fasteners.  

 

The risk of Hydrogen Embrittlement is noticeable in this second group, the Hardened Bolt, Nut, and Stud group, particularly in the galvanizing process to protect the surfaces of 10.9 and 12.9-grade fasteners. It is mandatory by the standards to print the strength markings, the manufacturer's logo or trademark on the bolt heads or the surfaces of the nuts.

 

Let’s remember that the first figure on the bolt heads shows one-tenth the minimum breaking strength of the bolt; the multiplication of two figures shows the minimum yield strength. Accordingly, the minimum breaking strength of an 8.8 grade bolt is 80 kg/mm² and the minimum yield strength is 64 kg/mm². In other words, an 8.8 grade bolt should not yield before 80 kg/mm² and should not break before 64 kg/mm². Similarly, a 4.6 quality bolt should not yield before 24 kg/mm² and should not break before 40 kg/mm².

 

    The bolts, nuts, and studs that are hardened, the ones with high strength are on the right side of the table and they are lightly darker colored to indicate hardening.

 

Looking at this table, we can say that the Risk of Hydrogen Fragility or Embrittlement occurs only on the right side of the table during the galvanizing of hardened high-strength Bolts, Nuts, and Studs.

 

In the fasteners that acid-cleaned before Galvanizing the hydrogen enters into structure increases in direct proportion to the hardness and the risk of fragility increases at the same rate.

 

 

It can be. For this purpose, the Bolts and Studs must be exposed to the Hydrogen Embrittlement Relief Temper at 200 - 210 ° C for 5 - 8 hours immediately after galvanizing.

 

Implementing the Hydrogen Embrittlement Relief Temper a few hours after the galvanizing would be useless.

 

Even if the hydrogen embrittlement relief temper applied longer to bolts and studs of 12.9-grade, i.e. with a minimum breakage strength of 120 kg/mm² or maximum hardness of 44 HRC, does not guarantee 100% hydrogen removal from the structure. Therefore, 12.9-grade bolts, nuts, and studs are not highly recommended for galvanization. However, some manufacturers that do not have sufficient knowledge on the subject also galvanize 10.9 or 12.9-grade bolts and apply (or so called apply) Hydrogen Embrittlement Relief Temper with improper mechanisms without even realizing that they put users at great risk.

 

 

It is not possible to see with bare eyes whether or not galvanized bolts and nuts are subjected to Hydrogen Embrittlement Relief Temper. It cannot be determined in the lab by simple tests such as hardness measurement or spectral analysis. Some under-the-counter production companies that are aware of this avoid a considerable cost element by skipping a critically important process. Thus, with the price that appears cheaper, they mislead the purchasing authorities in the process of price comparison and leave the consumers, who focus on price rather than quality, to face the Risk and Results of Hydrogen Embrittlement by themselves.

 

 

Those who have to use galvanized bolts can prevent the irreparable material and moral losses and find out whether the bolts carry the risk of Hydrogen Embrittlement by having them tested with the devices developed for this work. (Bolts, nuts or studs sent to Berdan Cıvata to be tested are passed through the test device and the results are documented from the Accredited Certified Laboratory.)

Some bolt manufacturers, who disregard the quality have a very dangerous second path to look cheaper for consumers: Using nuts of the low quality as well as of the low price.

 

All studs or bolts required to be used with the equivalent grade nuts by the standards.

 

With a 4.6-grade bolt a 4-grade nut, with a 10.9 grade bolt or stud a 10-grade nut must be used.

 

But today it is often observed that; with the 8.8 quality bolts, instead of using the nuts of the same quality or strength that required by standards, ie strengthened to 80 kg/mm² by hardening, some manufacturers use cheap nuts with 5 (50 kg/mm²) strength but stamped as 8 (80kg/mm²) from Far East that merely invaded our country to mislead consumers leading to an unfair competition with quality manufacturers. By misleading consumers who focus on prices rather than the quality, they oblige them to make the wrong choice.

 

Many consumers who think that they purchased cost effective bolts and nuts come to their senses only after serious inspection personnel performing a torque or a slight earthquake resulted in irreparable damage.

 

If the TSE Inspections that removed from the customs in 2006 are put back into force, many industrialists and builders in our country who do not have the means of testing will be able to avoid the material and moral damages caused by this deceit and our quality-focused producers will not be victims of unfair competition.

 

 

Of course can be. Acids, due to their burning, chewing and irritant traits they cause the teeth of the bolts to lose the strength if they are kept or forgotten in the acid bath for a long time. 10.9 and 12.9-grade hardened bolts, nuts and studs become fragile due to thinning out. 

 

They also cause great harm to the environment and employees. They cause wounds in the respiratory tract and in the lungs of those who inhale the steam. It causes very inconvenient results when it splashes on skin and eye. When acid residues are poured into water or soil, they kill microorganisms. 

 

A number of R&D studies were carried out at Berdan Cıvata to eliminate these multifarious damages caused by acids on bolts, employees and the environment. As a result of these studies, the bolts and nuts were cleaned by using mechanical means instead of acid. Thus, the damage on employees, the environment and hardened bolts caused by acid in the galvanizing process was completely prevented. Thus, galvanizing of the 10.9-grade bolts which known up until yesterday that cannot be galvanized due to the Risk of Hydrogen Embrittlement, the 12.9-grade bolts & studs which known that, even with a long-term Hydrogen Embrittlement Relief Temper, 100% removal of hydrogen from the structure cannot be guaranteed became possible without any problem and risk.

 

Berdan Cıvata San A.Ş has obtained the patent from the Turkish Patent Institute for the Eco-friendly Immersion Galvanizing Method which prevents the Risk of Hydrogen Embrittlement which has become a nightmare for fastener producers and the users of 10.9-grade dipped galvanized Bolts, Nuts, and Studs especially in steel structures.