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 Post subject: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 6:50 am 
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My 1/8" BSPT - 4 AN sheridised steel fittings have corroded! Have these been sheradised or are they suppose to be yellow in colour like the one's in the fitting catalog, part #1090. I can't get a good photo further inside the bore but the deposits are big enough to block a fuel jet, and that would really piss me off. I suggest this part not be on the catalog and replaced with a stainless steel equivalent. Harsh, but I'm MAD!!

I have not had any type of media go through this yet, I was about to make the lines and spotted the corrosion on the tips of the flare. I may just use a readily available 1/8" NPT - 4 AN aluminium part from Earls.

Paul
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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 12:29 pm 
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Very sorry to hear you've had such a problem and the only thing I can think that could cause such an issue, is that you live in an area with some kind of unusually corrosive element in the air, as nothing corrodes without something in the surroundings to cause it. :?

Those components are one of the few that we don't actually make ourselves but as a consequence they are items that are sold by the 1,000s by a range of companies (including Goodridge) and as we've never had a problem with them before (even when in use), we've had no reason to think they were inadequate for the job.

FYI we manufacture all the components that we sell large quantities of but untill recently, conversions to US spec fitting (in this case 4AN) have not been in big enough demand to warrant making them ourselves. However, the demand has been progressively increasing and as a consequence we are just waiting for a batch of suitable fittings for this job to be finished in stainless steel.

When they are completed I'd be happy to send you replacements but that could be a few more weeks yet.

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 12:48 pm 
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With regard to the type of protective finish and the colour of it. Depending on the source we buy these from, they are either zinc/cadmium plated (a dull silver/grey finish) or they are sheradised, which as you've mentioned has a yellowish tinge to it. Both finishes should give a high degree of anti corrosion properties to the components they are applied to (under 'normal' condition of 'use'), so it's very strange that you should have such a problem JUST in atmospheric conditions.

I've just carried out a search to see if I could find any info on zinc/cadmiums anti corrosion capabilities and to see what it might react with to cause the level of corrosion you've experienced but I could only find general statements such as "Cadmium is highly resistant to corrosion and has been widely used for electroplating of other metals, mainly steel and iron. Screws, screw nuts, locks and various parts for aircraft and motor vehicles are frequently treated with cadmium in order to withstand corrosion" and nothing 'relative' about why or what would cause it to corrode/oxidise.

If I were you I'd be a bit worried about what I was breathing, that could cause such a highly corrosion resistant metal to corrode so readily, because it's my bet that it can't be much good for you. :idea: :(

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 1:10 pm 
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Found the following info after further searching;

Some metals have naturally slow reaction kinetics, even though their corrosion is thermodynamically favorable. These include such metals as zinc, magnesium, and cadmium. While corrosion of these metals is continuous and ongoing, it happens at an acceptably slow rate. An extreme example is graphite, which releases large amounts of energy upon oxidation, but has such slow kinetics that it is effectively immune to electrochemical corrosion under normal conditions.

Which indicates its highly suitable for the job, as does the following extract which also explains why it's been localised and so quick BUT gives cadmium as a cure. :?

Platings usually fail only in small sections, and if the plating is more noble than the substrate (for example, chromium on steel), a galvanic couple will cause any exposed area to corrode much more rapidly than an unplated surface would. For this reason, it is often wise to plate with a more active metal such as zinc or cadmium.

Still unable to find anything that indicates the plating would be a problem and everything I've read points to a corrosive media being responsible, which on an unused component as in your case, can ONLY be in the air. :(

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 1:30 pm 
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One more thought; if the fittings had been put to use immediately they were fitted, the media they were flowing (fuel and nitrous), would have excluded whatever is currently causing the oxidation/corrosion from the inside of the fitting, preventing any corrosion that could cause a blockage. Cleaning the corrosion off the parts just before 'actual use' and applying a small amount of lubrication to the outside, should stop any further corrosion and normal flow of fuel & nitrous 'SHOULD' prevent any internal corrosion, as the air (which seems to contain the corrosive element) will be excluded.

If you had the time to do this and carry out a few checks, it would be interesting to see the results. It would also be interesting to discover what it is in the air over there, that can counteract the anti corrosion characteristics of the plating.

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 1:33 pm 
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I just read another site about corrosion, do you by any chance live near the sea?

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 9:31 pm 
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Hi Trev, thanks for the many replies. I live about 10km from the coast, but the corrosion was internal only, I had AN caps on them to stop debris getting in while driving. What I think may of happened is, when I was bending and cutting the SS hard lines I used compressed air to clear the lines of anything, as you know sometimes a small compressor will have water in it especially in humid conditions like Australia. Maybe a bit of water got in, I then put the AN caps on and the corrosion went to work. I would assume that anti corrosive coating whatever it may be would be impervious to water also.

Anyway, the cause isn't the problem now it's more the solution. I'm thinking of re-tapping the thread with an NPT tap and using an aluminium fitting.

Paul

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sat Feb 12, 2011 9:53 pm 
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This is what I scraped out with a drill bit, they look bigger than they actually are because of the macro zoom on the camera. It was even corroding around the AN cap just on the inside of the ring where it was sealing on the flare.

Paul
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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sun Feb 13, 2011 12:19 am 
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The reason I asked about how close you were to the sea, was because there was a mention on a website that corrosion is much worse the closer you get to the see due to the salt.

Your explanation makes sense and although I'm SURE the water alone didn't cause the corrosion, there was probably other elelments in the water that did.

Be careful screwing alloy parts in to alloy parts, as they can easily sieze, so I'd recommend applying some PTFE PASTE when you assemble them.

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sun Feb 13, 2011 1:58 am 
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Yeah I always use PTFE paste on nitrous fittings, loctite 515 (which is a flange gasket sealer but works really well) on fuel fittings and Nickel anti-seize on AN fittings (threads only).

Paul

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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Sun Feb 13, 2011 11:31 am 
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This type of corrosion used to happen alot on electrical equipment when they first started using dissimilar metals, had to use all sorts of different compounds on joints to stop it, even in dry environments .


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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Thu Feb 17, 2011 11:27 am 
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Got new aluminium fittings on, luckily the NPT thread was slightly bigger than the BSPT so I was able to tap complete threads. Had to cut a tap down just over 7mm to get the new fittings to almost bottom out at the bottom of the threads of the Y-block, so that the internal bore has minimal disruption between fitting and Y-block.

Paul
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 Post subject: Re: Sheradised steel fitting corrosion!!
PostPosted: Thu Feb 17, 2011 1:07 pm 
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