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USnavy
Aug 25, 2009, 5:39 AM
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Recently there has been a little battle around here as to whether hardware bought stainless steel U-bolts are safe for climbing. One party uses Fixe brand stainless U-bolts and the other uses hardware store bought stainless U-bolts. I was rather interested in knowing the answer to this so I set out to find out.
I tested some of Fixe's u-bolts as well as some stainless steel 3/8" u-bolts I bought from Lowes. In the end I found that both were completely bomber and there are no strength issues using store bought u-bolts. Every u-bolt I got from Lowes held over 35 kN in tension mode.
So the next factor to research to determine the suitability for store bought u-bolts is corrosion resistance (the bolts are used in a marine environment). I contacted the manufacturer of the hardware brand u-bolts and they stated the bolts are made of grade 304 stainless steel. Fixe's u-bolts are made out of A304 SS. So, is it possible that the Fixe brand 304 SS bolt can exhibit better corrosion resistance (SCC, pitting, ect.) to salt water then the hardware store brand 304 SS bolts, or is all 304 SS completely identical? Now I know that Fixe lists their bolts as being A304 and not 304. Does A304 have the same corrosion resistant capabilities as standard 304?
(This post was edited by USnavy on Aug 25, 2009, 8:29 AM)
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hafilax
Aug 25, 2009, 1:35 PM
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316 is the high corrosion resistance grade. I doubt you'll see a noticeable difference within the 304 grade.
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jdefazio
Aug 25, 2009, 1:49 PM
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There isn't any "A304" grade of stainless steel, so you could always contact Fixe to inquire what they are really getting at with the "A" designation. The A-type might refer to a particular annealing designation, but it should be uncommon for 304SS to be sold in a work-hardened state anyway, so that would likely be a redundant description.
Regarding corrosion resistance, that is mostly determined by the surface condition and passivation process. While most will be similar, you can't know anything specific about this just by the type designation of the base material. In that regard alone, no, all 304SS is not identical.
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scion
Aug 25, 2009, 2:35 PM
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I think Fixe is using a non-standard nomenclature; I've never come across A304 before. You'll sometimes see 304 stainless referred to as A2, so maybe they've gotten confused?
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kennoyce
Aug 25, 2009, 3:08 PM
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To answer your question, no not all grade 304 stainless is the same, but you say this is for a marine environment, so you shouldn't be using 304 anyway. For marine environments you should be using 316 stainless or you will have corrosion issues.
One more thing, you asked about SCC, these are glue-ins so there is not a constant stress on the bolts, therefore you won't get any SCC.
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JimTitt
Aug 26, 2009, 7:11 AM
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I doubt it is Fixe that is confused!
Iin their catalogue they write AISI304.
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miklaw
Aug 26, 2009, 7:38 AM
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Actually there are significant residual stresses at the bends and also in the rod from cold drawing. But it shouldn't matter unless you're in thailand
(This post was edited by miklaw on Aug 26, 2009, 7:39 AM)
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billcoe_
Aug 26, 2009, 1:48 PM
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Mike Law is right. On the earlier posters - A304 is the same make up of "stainless" material. It's the designation 18-8 which covers several similar grades of 300 series stainless that have minor variations. The 18 means 18% chromium and 8% nickel. However, there can be significant differences despite the identical head mark or designation. The finished material can be lathed (a Landis thread cutter for the threads) or cold rolled, and the different mfg methods will give you different strengths. Furthermore, and of much more importance to you, for corrosion resistance, if the stainless is not passivated (hit it with a real real good magnet to determine) then residual partials of carbon steel left over from the manufacturing can and will start the ball rolling much quicker on corrosion.
So all A304 is and is not the same, if that answered the question.
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JimTitt
Aug 26, 2009, 8:23 PM
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One problem is that the AISI grades are somewhat coarse and a direct comparison to Euro grades (which in fact are what Fixe use) is not always possible. Further confusion comes when in the AISI grades suffix letters are used, there being 4 grades of 304. Not knowing the difference between 304 (1.4301 & 1.4303) and 304L (1.4306) most probably caused the death of a climber in Europe a few years ago due to weld embrittlement.
AISI316 is worse still with 7 specified grades and this alloying band is covered by 11 European grades.
AISI 304 can contain 17.5-20% Cr and 8-10.5%Ni, just piling in more chromium however doesn´t improve things much making the material substantially weaker, higher grades generally having lower amounts of chromium and nickel but more molybdenum for example.
Better still are the Duplex and Super-Duplex steels which are a mixture of austenitic and ferritic iron and can tolerate higher chromium contents, these are both much stronger and more corrosion resistant than the more normal grades.
Using a magnet is no indication of the corrosion resistance of stainless steel, whether it is magnetic is a question of it being martensitic or austenitic. 304 and 316 are austenitic but become martensitic after a certain amount of working.
To test for surface corrosion resistance there are a number of standard tests, mostly involving warm salt spray then immersion in copper sulphate solution. This only tells you there is no surface contamination.
For internal corrosion resistance you need the intergranular analysis which is done with an electron microscope, this is supplied with the mill certificate for each batch of material.
To prevent crevice corrosion the bend radii need to be chosen carefully to prevent surface cracking which is where the failure starts, this is easily checked optically at about 600X magnification or with an SEM. And polish the shit out of the things!
Jim
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dingus
Aug 26, 2009, 8:37 PM
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So to put it in layman's terms...
no there is no real difference between 304s.
DMT
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majid_sabet
Aug 26, 2009, 9:00 PM
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USnavy wrote: Recently there has been a little battle around here as to whether hardware bought stainless steel U-bolts are safe for climbing. One party uses Fixe brand stainless U-bolts and the other uses hardware store bought stainless U-bolts. I was rather interested in knowing the answer to this so I set out to find out. I tested some of Fixe's u-bolts as well as some stainless steel 3/8" u-bolts I bought from Lowes. In the end I found that both were completely bomber and there are no strength issues using store bought u-bolts. Every u-bolt I got from Lowes held over 35 kN in tension mode. So the next factor to research to determine the suitability for store bought u-bolts is corrosion resistance (the bolts are used in a marine environment). I contacted the manufacturer of the hardware brand u-bolts and they stated the bolts are made of grade 304 stainless steel. Fixe's u-bolts are made out of A304 SS. So, is it possible that the Fixe brand 304 SS bolt can exhibit better corrosion resistance (SCC, pitting, ect.) to salt water then the hardware store brand 304 SS bolts, or is all 304 SS completely identical? Now I know that Fixe lists their bolts as being A304 and not 304. Does A304 have the same corrosion resistant capabilities as standard 304?
show us your test result and let us see it.
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adatesman
Aug 27, 2009, 12:57 PM
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dingus
Aug 27, 2009, 1:55 PM
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adatesman wrote: dingus wrote: So to put it in layman's terms... no there is no real difference between 304s. DMT I think you've got it backwards, Dingus.... The way I read it is that there is significant difference between the 304s.
You must have read a different thread then mate. Significant to CLIMBERS, how, specifically? I don't see anything of any use to any climber, up there.
DMT
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adatesman
Aug 27, 2009, 2:04 PM
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dingus
Aug 27, 2009, 2:06 PM
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How does that translate to a stainless steel purchase for a climber, please?
DMT
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adatesman
Aug 27, 2009, 2:10 PM
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dingus
Aug 27, 2009, 2:16 PM
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adatesman wrote: By a climber purchasing said material to make their own glue-ins, as appears to have happened in the accident that Jim's referring to. Barstock is fairly cheap, and if you have a way to bend and weld it making a welded eye glue-in isn't exactly rocket science. But you've got to know what you're doing with the material selection....
OK you are correct. There may be a nugget of useful information up there. If I ever make some glue-ins I will keep this in mind.
I can't see the average climber quizzing the average phone call clerk at the average outdoor retailer about various grades of 304 stainless (that none of the participants know the first thing about).
DMT
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kennoyce
Aug 27, 2009, 2:23 PM
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In reply to: Actually there are significant residual stresses at the bends and also in the rod from cold drawing. But it shouldn't matter unless you're in thailand
great point, I was completely neglecting the methods of manufacturing of the bolts and only thinking of the methods of attachment to the rock. I retract my previous statement about SCC not being relevant in glue-ins.
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adatesman
Aug 27, 2009, 2:30 PM
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JimTitt
Aug 27, 2009, 6:51 PM
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It happens.
A gentleman well known (or rather
ėnfamous´) in Austrian mountaineering circles obtained a supply of 304 but unfortunately this was one of the machining grades. He then bent and welded this into bolts. the weakest tested was unable to hold the weight of the tester and estimated to hold less than 5kg.
An Italian company has on the market bolt hangers stamped 316 and 25kN (and EN959). They fail axially at ca 8kN and radially at around 18kN. The material samples give an ultimate tensile strength of 362N/mm˛ which is nearly a half of that specified for 316.
Not all stainless steel is created equally and only known material from a reputable supplier AND with a works certificate should ever be used for climbing equipment. Even then I would suggest some testing is in order just to be sure.
It is also of great help if the purchaser has been provided with the intellectual tools to make best use of the vast amount of information on the materials available.
For the average home bolt maker a works certificate is an expensive luxury though some suppliers might help by including your order in a larger batch, the only other answer, as USNavy has done is to test the stuff.
Hardware store stuff varies from excellent to horrific and without breaking it you will never know, alternatively get a sample to a lab for testing. Surface mass spectrometry is useless as the typical Chinese product is electropolished to death, effectively it is melted down Mazdas which have been chrome plated so you need to cut through to get a meaningful sample.
For manufacturers it is relatively simple, all the ones I know only use European manufactured stainless with a works certificate and batch test each delivery of material. I (and probably others) break every hundredth bolt as well to be sure.
I break 1 in 25 welded products as these are more likely to give problems.
I test chain with 5 random links per coil (50m) and every 50th link while cutting the chain lengths.
Quality pays, in the end.
Jim
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USnavy
Aug 28, 2009, 4:57 AM
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adatesman wrote: By a climber purchasing said material to make their own glue-ins, as appears to have happened in the accident that Jim's referring to. Barstock is fairly cheap, and if you have a way to bend and weld it making a welded eye glue-in isn't exactly rocket science. But you've got to know what you're doing with the material selection....
That is if bolt one is made out of 304 SS and bolt two (from a different manufacturer) is made out of 304 SS will they exhibit similar corrosion resistance values. We already know that standard 304 SS hangers and bolts have a life span of about 10 - 15 years out here. The ultimate question is will these 304 SS hardware store U-bolts last just as long sence they are also 304 SS?
(This post was edited by USnavy on Aug 28, 2009, 5:07 AM)
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USnavy
Aug 28, 2009, 5:08 AM
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majid_sabet wrote: USnavy wrote: Recently there has been a little battle around here as to whether hardware bought stainless steel U-bolts are safe for climbing. One party uses Fixe brand stainless U-bolts and the other uses hardware store bought stainless U-bolts. I was rather interested in knowing the answer to this so I set out to find out. I tested some of Fixe's u-bolts as well as some stainless steel 3/8" u-bolts I bought from Lowes. In the end I found that both were completely bomber and there are no strength issues using store bought u-bolts. Every u-bolt I got from Lowes held over 35 kN in tension mode. So the next factor to research to determine the suitability for store bought u-bolts is corrosion resistance (the bolts are used in a marine environment). I contacted the manufacturer of the hardware brand u-bolts and they stated the bolts are made of grade 304 stainless steel. Fixe's u-bolts are made out of A304 SS. So, is it possible that the Fixe brand 304 SS bolt can exhibit better corrosion resistance (SCC, pitting, ect.) to salt water then the hardware store brand 304 SS bolts, or is all 304 SS completely identical? Now I know that Fixe lists their bolts as being A304 and not 304. Does A304 have the same corrosion resistant capabilities as standard 304? show us your test result and let us see it.
I shall. I am currently conducting tests on machine bolts glued into the rock that are used as climbing bolts. I also want to run some tests on the titanium u-bolts we actually use here for climbing. When the results are in I will post them.
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JimTitt
Aug 28, 2009, 7:27 AM
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Stainless steel grades are bands and not defined compositions. AISI304 is specified as:-
Component Wt. %
C Max 0.08
Cr 18 - 20
Fe 66.345 - 74
Mn Max 2
Ni 8 - 10.5
P Max 0.045
S Max 0.03
Si Max 1
EN 1.4301 is not exactly the same.
To obtain the corrosion resistance one then calculates the PRE. The Pitting Resistance Equivalent number (PRE) has been found to give a good indication of the pitting resistance of stainless steels. The PRE can be calculated as:
PRE = %Cr + 3.3 x %Mo + 16 x %N
Which, if you have the works certificate which contains an alloy analysis gives you what you are asking.
Note that the nitrogen content is not specified by AISI but is a large factor in corrosion resistance. The nitrogen content varies with the smelting process used so varies with the manufacturer.
The addition of molybdenum allows the nitrogen uptake to be increased.
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