Does G70 Have Risk of Hydrogen Embrittlement?

0

Mention galvanized G70 chain in any discussion, and one of the first comments will be a question of the risks of hydrogen embrittlement. Though hydrogen embrittlement is very real, there have been no well-publicized cases of galvanized G70 anchor chain failure, nor cases of hydrogen embrittlement in new galvanized G70 anchor chain, and negative comment is apocryphal, in our opinion. Scare mongering at its best, or worst.

Hydrogen embrittlement is a result of pressure derived from concentrations of hydrogen atoms within a metal structure causing microcracking producing catastrophic failure. The hydrogen can be within the metals steel crystalline structure or introduced to the surface of the steel as a result of processing-commonly through pickling, or in the case of marine chain, acid-cleaning prior to galvanizing. Low carbon and higher hardness, which includes high-tensile steels, can be prone to hydrogen embrittlement. Hydrogen embrittlement is not an issue with mild steels because of their ductility.

The phenomena of hydrogen embrittlement are well known (there is not one single cause) and documented. There are a number of techniques to overcome the problems as, for example, additions of certain alloying elements to the steel and/or variation to the galvanizing bath chemistry will reduce susceptibility. Each of the companies making galvanized G70 chain has its own proprietary techniques to ensure hydrogen embrittlement is not an issue.

We tend to think only of Acco in terms of galvanized G70, but for example, Pewag and Gunnebo also produce galvanized G70 (but specialize in G100 and G120 lifting chains). Since galvanized G70 chain was introduced for anchoring, there have been no reported incidences of failure through hydrogen embrittlement, and it merits mention that each of the current participants have been making G70 chain and galvanized G70 for years. Possibly beware new entrants-at least initially.

One downside of G70 chain is that it should not be re-galvanized by anyone other than a galvanized G70 maker (none of whom currently offer the service as it is uneconomic). A normal, sub-contract galvanizer is very unlikely to have a galvanizing bath chemistry and process focused at minimizing hydrogen embrittlement in G70 chain, and there have been issues with re-galvanizing high-tensile steel in the past.

An equally serious issue with high-tensile chain is stress corrosion, cracking caused at the crown, or bend, of each link. Bending high-tensile steels through a tight curve, like a chain link where the inside of the wire is compressed and the outside of the wire stretched, demands caution; incorrect processing can result in cracking and catastrophic failure. Again, experience counts, and the marine industry is lucky as G70 chain production benefits from the trickle down technology of G100 and G120 chain production. Process techniques are available to ensure stress corrosion is not an issue.

Other than expertise (and maybe hard-won experience), galvanized G70 manufacturers all currently proof test to 50 percent of breaking strength, or twice the working load limit, every link of the galvanized chain they sell.

Armorgalv-coated, high-tensile steel is said not to be susceptible to hydrogen embrittlement, as the coating is permeable by hydrogen. We cannot conduct tests to verify the claims, but data does suggest the claims are correct. Certainly, it has been possible to Armorgalv coat even a G120 lifting chain, and if there were an issue, it would show up with such a high-tensile product. However, chain makers also claim their processes are such that hydrogen embrittlement is not an issue with G70, and at least one chain maker, Campbell, has successfully worked with a galvanized G80 product.

Practical Sailor has been independently testing and reporting on marine products for serious sailors for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising or any form of compensation from manufacturers whose products we test. Testing is carried out by a team of experts from a wide range of fields including marine electronics, marine safety, marine surveying, sailboat rigging, sailmaking, engineering, ocean sailing, sailboat racing, and sailboat construction and design. This diversity of expertise allows us to carry out in-depth, objective evaluation of virtually every product available to serious sailors. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser with more than three decades of experience as a marine writer, photographer, boat captain, and product tester. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.

LEAVE A REPLY

Please enter your comment!
Please enter your name here