High strength nut/bolt for marine application
High strength nut/bolt for marine application
(OP)
I have been researching materials for use in a marine fastener application, but could use some input from some of you with experience. We have a part with a socket hex drive and 3/8-16 UNC thread and a mating square captive nut. The parts will be completely submerged in seawater for most of their life. The nut in particular is captive in a closed pocket where seawater will likely collect and become stagnant. I believe this will create a significant risk for crevice corrosion. High strength is required for these components in the range of 80 ksi yield or better.
We have used monel 400 or 500 for similar applications but there have been reports from our production staff of the hex drive stripping out easily during assembly. I am thinking this phenomenon is limited to the 400 alloy since it is not as hard, but I don't know because our drawing allows fabrication from either.
We have also used Inconel 718 for similar applications and I am leaning toward using it for at least one component here. I am concerned about galling between the nut and bolt. These parts may be disassembled on a monthly basis and I don't want them to lock up. Is there another comparably strong and corrosion resistant material that would work well with 718 for the mating part? We have used Nitronic 60 and Ni-Al-Br to prevent galling in the past but I don't think either is suitable for this application.
Also of note, we need a way to assemble these components so that they will resist loosening from vibration. Threadlocker seems like a good solution so I don't think lubricating the threads is an option to prevent galling.
Thanks
We have used monel 400 or 500 for similar applications but there have been reports from our production staff of the hex drive stripping out easily during assembly. I am thinking this phenomenon is limited to the 400 alloy since it is not as hard, but I don't know because our drawing allows fabrication from either.
We have also used Inconel 718 for similar applications and I am leaning toward using it for at least one component here. I am concerned about galling between the nut and bolt. These parts may be disassembled on a monthly basis and I don't want them to lock up. Is there another comparably strong and corrosion resistant material that would work well with 718 for the mating part? We have used Nitronic 60 and Ni-Al-Br to prevent galling in the past but I don't think either is suitable for this application.
Also of note, we need a way to assemble these components so that they will resist loosening from vibration. Threadlocker seems like a good solution so I don't think lubricating the threads is an option to prevent galling.
Thanks





RE: High strength nut/bolt for marine application
http://www.tachart.com/material/marinel-220/
https://www.copper.org/applications/marine/cuni/al...
http://www.azom.com/article.aspx?ArticleID=1732#_T...
https://www.nickelinstitute.org/~/media/Files/Tech...
RE: High strength nut/bolt for marine application
As a first step I would require K500, with no options. You do require that these for formed (either cold or warm, but never hot), and then threaded and aged? The sequence is critical.
Marinel is a good option.
A "C" alloy (276, 22, 622, 686, 59, ...) would also give you the desired corrosion resistance.
When it comes to galling using dissimilar metals usually helps, so mixing Marinel and K500 should be a good combination.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
I should mention this is a very low volume application. This may impact material selection and mfg processes mentioned. I am going to check with a couple of our material suppliers, but is Marinel readily available or is a mill run required?
Thanks very much for the suggestions, this is very helpful information.
RE: High strength nut/bolt for marine application
I have also seen K500 bolts that were made wrong, they had variable grain size with coarse structure at the shank-head transition. These bolts failed at low loads even after proper HT. There are people out there making K500 bolts regularly, and doing it right.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
I don't know.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
I have been reading as much as possible and did see mention of corrosion of Cu based alloys in seawater near land due to contaminants from waste.
I think I may be over-emphasizing the galling requirement. Offshore/Oil&Gas/Marine bolting IAW A193 and A194 recommend 316 bolts with 316 nuts which would seem to represent a horrible combination for galling. Also, in literature regarding offshore and marine bolting, galling comes up surprisingly few times.
Ed - While 625 and 718 suffer crevice corrosion, it seems like K500 is susceptible to hydrogen embrittlement, correct? Also, what is the mechanism that causes a material that has been hardened to corrode in seawater as opposed the same material in its annealed condition? Does this also apply to age hardened alloys like K500 and 718?
Would a K500 fastener and C276 or Inco 686 nut make sense? Could I get away with something cheaper for the nut?
Another detail, the majority of the system is composed of thick, forged 316L tubing.
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
The strengthening mechanism in K500 has no impact on its corrosion resistance. I have only seen hydrogen embrittlement in material that was heavily cold worked and direct aged.
718 has mediocre aqueous corrosion resistance in any condition. I did a bunch of slow strain rate testing and it is susceptible to Cl induced cracking. The K500 and 25-6Mo were not.
A 6%Mo alloy should work, but in fasteners a Ni alloy will be the same price.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
Good to check though.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
http://www.nace.org/cstm/Store/Product.aspx?id=2a6...
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
Actually produced, not really
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
I'm only basing my comment on a single site, is C22 hard to get? Keep in mind these are designed parts, we cannot use standard fasteners for this application. Qty will likely be in the 200-300 range total for each part.
Another question, among other things, I have been referring to Norsok M-001 and EEMUA 194 for some guidance on materials selection. Are these viable sources? I ask because EEMUA practically writes off Monel because of failures, and M-001 doesn't even mention it. We have been using small Monel K500 SHCS screws on "wetted" parts of our system for decades without issue. We also use quite a few very high strength 718 SHCS in probably the most critical structural connection that we deal with, again without any issue that I know of.
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
Like most alloys dependent upon a heat treatment process, or processes, if it is not carried out correctly the material could be rendered extremely susceptible to hydrogen embrittlement. The good experience with the Monel screws could be down to correct vendor selection, amenable dimensions for good heat treatment,low stress regime, and so on. It's not a foregone conclusion that cracking will occur, but the likelihood side of a risk assessment does start to head upwards. Issues did arise with N07718 processing resulting in the generation of API Std 6A718, and then API Std 6CRA. The latter document may well be worth a review to get an idea of key quality control requirements.
It was a DNV report, 2002-3301, that effectively killed off K500 for the oil and gas industry, and that is promulgated in EEMUA 194.
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: High strength nut/bolt for marine application
But in simple seawater service (provided that it isn't heavily cold worked and direct aged) it works well.
C22 is a good option.
I used to make high strength shafts and we saw issues with 718, found that heavily cold worked 625 did better even though it wasn't perfect.
We had K500 fasteners (Ferry cap head style) custom made in quantities of a few hundred at a time.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
"When I worked for Weir Materials we supplied a lot of lightly cold worked superduplex stainless steel fasteners (UNS S32760) (strength equivalent to B7 steel) with solution anneraled nuts. These have given good resistance to crevice corrosion in seawater up to ~35°C without galling because of the hardness difference beteen lightly cold worked and SA material. If these fasteners are to be CP'd subsea, they will pick up hydrogen, but failures will not occur unless the fasteners are stressed close to the 0.2% proof stress (>95%), which is rare for fasteners."
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: High strength nut/bolt for marine application
We are considering using a coating to reduce the likelihood of galling as well. Maybe an electroless nickel or TDC?
Glenn - thanks for the two papers. I had already reviewed the Nidi paper, but I am trying to get my hands on the other one.
RE: High strength nut/bolt for marine application
Just two things to keep in mind.
1. The nut and bold should have different hardness (either same alloy in two different conditions or two different alloys) to minimize galling risk. The nuts are usually the softer part.
2. The bolts should have rolled threads (this is part of why the bolts are usually stronger).
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: High strength nut/bolt for marine application
RE: High strength nut/bolt for marine application
SAE J1781 Materials for Fluid Systems of Marine Vehicles
SAE J2270 Ship Systems - Fasteners - Test, Inspection and Installation Requirements
SAE J2280 Ship Systems and Equipment - Fasteners - Selection and Identification Requirements
SAE J2295 Fastener Part Standard - Cap Screws, Hex Bolts, and Hex Nuts (Inch Dimensioned) [for ships]
SAE J2295M Fastener Part Standard - Cap Screws, Hex Bolts, and Hex Nuts (Metric) [for ships]
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: High strength nut/bolt for marine application