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There has recently been a series of high profile bolt failures on 'The Cheesegrater' in London, which have been attributed to hydrogen embrittlement.

What can engineers do to ensure that hydrogen embrittlement doesn't effect their structures?

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There are a number of standards to address hydrogen embrittlement in the manufacture and coating of fasteners. Here in the US, ASTM F1940 and ASTM F519 would apply. Hydrogen embrittlement is also a concern for structural welds, but should be addressed by your welding code.

The problem doesn't seem to be in the spec as often as in the quality control at the point of manufacture. In situations where this is a big risk, requiring third party inspections and testing are likely the most effective step the engineer can take.

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Like any number of engineering problems, solutions for hydrogen embrittlement fall into two categories: 1) prevention and 2) cure.

"Embrittlement," in this context, arises from the diffusion of hydrogen into metal. If it is not too severe, a possible cure is "reverse diffusion" that takes hydrogen away.

The cure doesn't always work, if the hydrogen finds its way into small pockets of metal and combines with other gases, e.g. carbon, to produce methane, a corrosive. Then, the only real solution is prevention.

One form of prevention is coating the metals to prevent contact with the hydrogen. In welding applications, it is also possible to separate the hydrogen from the metal by heating the metal.

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I know it's an old thread, but I'm putting my solution on here because I've just come across this issue.

Understanding the causes could help you deal better with hydrogen embrittlement.

Overstressing: Primarily, extra stress put on material results in the form of blisters, cracks, hydride formation on the structures. In this case, the atomic hydrogen present in the atmosphere reacts with the material. This could lead to hydrogen embrittlement.

Electroplating Steel: Hydrogen embrittlement also occurs while plating and pickling due to the exposure of the parts to hydrogen. The only solution to prevent this baking the part immediately after plating. A typical temperature is to bake at 375ºF for 4 hours within 1 hour after plating.

Tensile strength > 145 KSI: High-strength steels, titanium alloys and aluminium alloys are most vulnerable to hydrogen embrittlement.

The following resources may be useful

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  • $\begingroup$ Aluminum alloys are not subject to hydrogen embrittlement. Steel susceptibility starts ate about 120 Ksi and gets worse at higher strengths . Blistering has nothing to do with hydrogen embrittlement, Hydriding has nothing to do with hydrogen embrittlement of steel : however , titanium does both hydride and hydrogen embrittle - two different mechanisms. $\endgroup$ – blacksmith37 Aug 8 '19 at 20:28
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Get a few books on the subject , eg, Hydrogen Effects in Metals, AIME, 1981 , and ISO 15156 ; if you want more than the misleading answers found on this forum. If you have a specific question , try Eng-Tips forum . The first thing you will find is the topic has a dozen names because it is so widespread. One thing you can eliminate is High Temperature Hydrogen Attack - wherein H dissolves into the steel and reacts with carbides to from methane causing cracking of the steel ; that has nothing to do with the subject topic( see API 941 ). One small facet of hydrogen cracking seems to be your question : High strength fasteners, hardness above Rockwell C 22 / yield strength above 90,000 psi , are subject to failure when exposed to about any corrosion or cathodic protection. Use larger, lower strength fasteners.

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  • $\begingroup$ I read the article about the "cheese grater" , It was not written by an engineer very familiar with hydrogen stress cracking ; hot dip galvanizing never caused hydrogen embrittlement. Read about Greenkote also ; vapor deposite + diffuse process, sounds fine , However , in a severely corrosive environment it will be consumed; but likely good for buildings and bridges. $\endgroup$ – blacksmith37 Aug 14 '17 at 21:28
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I do have a commercial interest however article below is relevant to the question asked.


Greenkote treated bolts to be used to repair Leadenhall Building.

London’s Leadenhall Building, or as it is more popularly known, the “Cheesegrater” hit the headlines again earlier this year when, not long after completion, reports of three of the giant studs securing the exoskeleton suddenly snapped and fell, in one case from the 15th floor, before landing on the ground.

Some of the studs used in the construction of the 738 ft. tower are reported as being approximately 72mm diameter. The distinctive wedge-shaped 52 floor tower is 738ft tall and is close to both the Lloyds Building and the Gherkin. It opened in July 2014 and was designed by Rogers Stirk Harbour + Partners

An analysis of the problem revealed the cause as hydrogen embrittlement, which usually occurs when hydrogen atoms diffuse into the steel and weaken the overall molecular structure, making it brittle and likely to snap suddenly. Often blamed as a side effect of galvanising, a process using acids, in this case the studs had not been treated, so the fault was probably down to a manufacturing error.

UK specialists Tension Control Bolts, whose products are being used in the assembly of the new safe containment shelter to encase the Chernobyl reactor in the Ukraine, were commissioned to identify a suitable solution and specified a Greenkote treated fasteners to replace the damaged and missing studs. The work is expected to be finished by the end of 2016.

The Greenkote coating process offers a number of critical advantages, depending upon the application. Using no acids, hydrogen embrittlement is avoided, whilst the process offers high corrosion resistance, excellent paint adhesion and exceptional levels of coating consistency. When coating threads, neither internal nor external surfaces need to be reworked. A small number of companies globally, including TC Bolts, are licensed to use the coating process. Mark Gore, CEO of Greenkote commented, “Greenkote’s thermal diffusion process offers exceptional corrosion protection and critically in this instance, protection against hydrogen embrittlement, as the coating does not rely upon aggressive acids at any stage. We are delighted that our system has been chosen to help repair this iconic new building so helping to ensure its success as a significant London landmark.”

For avoidance of ambiguity TCB Ltd did not manufacture or supply the sub-standard steel studs; rather we Greenkoted the replacement studs.

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