Doxsteel Coating

Tested for the Toughest Industrial Environments.

When we decided to search for a better way to coat fasteners, we started by determining a list of requirements. We wanted a coating that could stand up to torquing forces and temperatures and not flake, burn, or break out and compromise the bolt’s integrity. We wanted the surface to have a consistent low coefficient of friction so torquing would be easier. We wanted a coating that would give our bolts a longer life cycle to help streamline the delivery and assembly process for our clients. And, most important of all, we wanted a fastener that would stand up to corrosion and resist seizing for a considerably longer time period than any other fasteners.

Nickel-Cobalt Alloy

The Brother-Sister Transition Metal Tag Team
Nickel-Cobalt (NiCo) is an alloy with a rich history. As transition metals that sit side by side on the Periodic Table, Nickel and Cobalt complement and strengthen each other. The alloy has been used in applications by both the military and NASA in environments where resisting corrosion and standing up to high temperatures are critical to success. Electro-deposited Nickel-Cobalt alloy is one of the materials promoted by NASA’s Technology Transfer Program, which is dedicated to bringing engineering advances used in outer space down to Earth for terrestrial applications. NiCo has also proven its mettle in subsea environments.

quote“Developed in response to a specific technology needed by NASAís Space Shuttle program, the method does not require the use of any organic additives beyond those used in traditional nickel plating baths. The technology also encompasses an in-situ monitoring system that periodically checks for the tensile strength and purity content of the deposit. This method and monitoring system can be used with any electrolytic plating process that requires a knowledge of deposit mechanical properties and/or chemical composition.”

NASA Technology Transfer Program

Cleaning

Surface preparation is the key element to any coating application process, so it is vital that our fasteners are decontaminated and free of flaws that can compromise their integrity. At Doxsteel Fasteners, we prepare our nuts and bolts for coating through a chemical surface preparation process that is controlled, tested, and monitored throughout. This is another way we reduce variability.

Electroplating

We coat our fasteners using a controlled electroplating process. After our nuts and bolts are tested and cleaned, they are placed in a bath with NiCo. Through electrolysis, we charge the bolt or nut, and the alloy is attracted to it, completely covering the entire part in a consistently thick protective coating.

Consistency makes the difference. Electroplating has two specific advantages over other methods of coating. The first is consistency. Throughout our process, the coating is applied evenly across the whole part and does not disturb the effectiveness of the thread. Electroplating systematically applies enough coating to meet the minimum requirement for the plating to work, but does not apply excessive coating so as not to interfere with the fit and function of the threads. Whereas in most fastener processes, the paint gets in the thread and affects the variability of coating from fastener to fastener, Doxsteel is able to control the layers of coating on each and every bolt.

By staying within this window of coating effectiveness, Doxsteel Fasteners lead to less overall downtime and remove the necessity of hot bolting for our customers and their turnaround teams.

Coating Comparison

Think inside the nut. The second advantage of electroplating is that we coat the entire part. In other coating processes such as hand-spraying or painting, pieces of the part such as the inside thread of the nut are not adequately covered. This lack of protection can compromise the integrity of the fastener before it has a chance to go to work, leaving it vulnerable to its environment. In the conditions that these fasteners are likely to operate, this lack of protection will cause the fastener to seize, requiring the use of costly hot bolting procedures, which will jeopardize lives and risk the facilityís entire operation.

The minimum and the maximum. Even though electroplating allows such consistency and makes sure that the whole fastener is coated evenly and effectively, there are still variables that require close control. The simple act of placing a bolt in the bath affects the bathís temperature. After a round of plating, some chemical components are lost. These variables, when left unmonitored, can undermine the effectiveness of the coating.

So we donít leave them to chance.

We determine how the part will affect the temperature and adjust to compensate, plating the part at the perfect starting temperature. We monitor what materials were consumed by the process and replace them, ensuring the chemical composition stays constant. Our goal is a controlled process with the narrowest margin for optimal performance, which is how we can stand by the consistency of Doxsteel Fasteners.

quote“On December 18, 2012, while the Transocean Discoverer India was performing drilling operations at the Keathley Canyon lease block in the Gulf of Mexico, the rigís lower marine riser package separated from the blowout preventer stack resulting in the release of approximately 432 barrels of synthetic-based drilling fluids into the Gulf of Mexico. Chevron, the designated operator, reported to BSEE that the incident was the result of the failure of GE H4 connector bolts on the LMRP…The failure of the bolts was primarily caused by hydrogen-induced stress corrosion cracking due to hydrogen embrittlement.”

Excerpt from “QC-FIT Evaluation of Connector and Bolt Failures: Summary of Findings,” Bureau of Safety and Environmental Enforcement, 2014

Hydrogen Embrittlement

Any plating process can produce hydrogen, and in hard parts such as industrial fasteners an uncontrolled process can lead to hydrogen embrittlement. This has been a major cause of fastener failure in the field for many years, and in some cases was the domino that led to major incidents that cost workers’ lives and completely shut down facilities.

Due to this serious threat, the industry has come out in favor of manufacturing and coating standards that prevent hydrogen from infiltrating micro-cracks in the substrate. Many bolting and coating companies bake their parts in high temperatures to evaporate the hydrogen that clings to the surface, and Doxsteel is no different. But thatís not all we do.

First, we have designed additives which reveal hydrogen bubbles and draw them to the surface to be released in the bath. This gives the hydrogen less opportunity to compromise the bolt’s integrity. Second, we constantly test all elements of the plating process, including the materials and chemistry that are susceptible to hydrogen. Currently, most industry standards only require a test once every 90 days to determine the process’ susceptibility. We test ours every 30 days. We want to see that every variable and additive is always under our control.

Hydrogen has many places it can enter a bolt, and you cannot always be 100% sure that you have eliminated it. So in addition to our frequent testing and use of additives, we bake out hydrogen from our nuts and bolts for a minimum of eight hours to evaporate the hydrogen. These three processes allow us to be as certain as we can be that hydrogen has been eliminated and will not lead to embrittlement.

Calculating the K Factor

To perform its vital role, a fastener must be installed properly. To provide proper installation, the team that is on the front line of these critical turnaround operations must be given the right tools for the job. Any company can produce a coating that resists harsh environmental conditions, but if the coating can’t stand up to the work done on the fastener and isn’t consistent when it comes to calculating required torque, then the bolt is compromised from the start.

To calculate a fastener’s required torque, a turnaround team needs to know the diameter of the bolt, the amount of tension the bolt will need to hold the flanges together, and all of the factors that act on the bolt to resist these forces. These resistance factors are very difficult to calculate and to keep consistent from fastener to fastener, which is why consistency was one of our top priorities when looking for a coating solution.

Our coating process maintains a consistent low coefficient of friction which makes torquing easier overall, but this consistency also allows us to reliably calculate the resistance factors and put them into a number that we can provide to turnaround teams: the K factor.

T = K * db * Fp

We place our fasteners’ K Factor on the side of every box and the user guide that comes with the box, so the torque value can be calculated and applied with ease. A dent in a bolt’s thread can have a 30% effect on its torque value, so our packaging also prevents the rigors of shipping and storage from affecting the K factor and compromising the fasteners’ integrity. This helps turnaround teams remove the risk of overtorquing the bolts, which could lead to larger operational issues. It’s another way Doxsteel Fasteners were designed for the end user.

?Learn more about how our packaging helps turnaround teams.

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