Supertanium is now part of Lawson Products. I have some date in my stack. There were several good articles written by their Chief Engineer; Elton McBroom when it was the Premier Industrial Corp. My article is dated April 1964
His lead in statement for the “The ways of Fastener Failures”:
“There is an impressive pile of ignorance atop the subject of nuts and bolts. This article will spade away the ignorance only if it scares the hell out of you-and you stay scared”
The Supertanium line of fasteners at one time were called the super 8; Q & T with a minimum tensile strength of 160,000 psi and at the time exceeded nearly all fastener specs.
I haven't looked at the Lawson site but they should have data for the fasteners.
Supertainium is just a marketing word. The parts that we looked at several years ago used a normal low alloy that would be used for grade 8 and it appeared that they used a slightly higher tempering temerature to get a higher tensile. No great shakes there. A standard Socket Head Cap Screw bolt will have a higher minimum Tensile (180KSI).
I try to stay away from all fasteners that use tricky marketing terms. It usually means that the money that they should have spent on high grade steel went into the Marketing budget instead. Stick to parts that proudly proclaim which concensus standards that they meet.
Screwman,
I would like to deviate from your post somewhat where it pertains to Supertanium Bolts. They have been around for over 40 yrs supplying maintenance fasteners to industry. I know of two papers mills and one powerhouse that have and continue to use the product with outstanding results. The are usually a bin type item and eliminate confusion and inattention by uniqueness of the head marking and the higher bolt heads, as wells covering all standard grades.
I grant you the fact that you can run down a fastener with proclaimed markings and sources, but one should be aware all that seems well is not well. As the number of the old line fastener manufacturers moved on , people have got to look around for different suppliers.
Case in point, our standard for years was Allen Mfg. and when they went belly up as a manufacturer of fasteners it was a scramble to find another quality supplier. Every manufacturer we tried we had quality problems. The Fastener Act didn't help, while NAFTA utterly confused the issue.
Here are the latest strength values for the Supertanium line of fasteners.
Minimum tensile strengths: 200,000 PSI (1/4 through and including 7/16 dia.); 190,000 PSI (1/2 through and including 5/8 dia.); 180,000 PSI (3/4 through and including 1-1/4 dia.)
I know there is an adjunct line of fasteners to Supertanium that have about a page of pedigrees. These are the type fasteners that you don’t normally have laying around to end up in a lawnmower or go-kart while at the same time you wouldn't want a nondescript fastener in a hydraulic pump. So there are maintenance fasteners and callout fasteners for special applications.
The Supertanium line of fasteners falls under the heading of non-confusing maintenance fasteners.
No, I don’t have any association with Lawson other than having a nice supply of Supertanium HHCS in my shop.
The standard finish (IIRC) on the Supertainium bolts is zinc with yellow chromate. With a UTS of 200KSI that will put the hardness level at about Rc 43. That is well into the danger range for hydrogen assisted cracking. Be careful of embrillement failures (I don't recommend electroplate on any commercial fastener over Rc 40) and don't use them in an application where they will exposed to corrosion. If they are loaded up to their full capability (which will take a lot of torque), and they see corrosion, there will sooner or later be a delayed SCC failure. The reason that most users of these type of parts get by without failures is that they never really load them up to their full capability. And if they are working at the lower clamp load values, then why use the higher strength parts in the first place. For safety against environmently assisted failures, you should always use the lowest strength fastener that will get the job done. Higher strength increases your risk of hydrogen assisted cracking.
If what you say is true in every sense of the word every airframe in air should be grounded and millions upon millions of fasteners in industry would have to be changed out.
Personally I can't see the concern you have over the Hydrogen issue and delayed cracking. It has been my experience that you don't encounter this problem that often unless you are in service that requires special considerations for the Hydrogen enviroment. There are other problems with fasteners that present far greater concerns than delayed SCC of alloy steel fasteners. I'll grant you that Hydrogen can be a problem with fasteners, but I can't see it to the extent you state.
I'll stick with Supertanium for this case as it seems you have a problem with the fastener. Yellow Zinc isn't not considered a corrosion resistant coating(100 hrs at best for 10% rust) in the real world. It is good enough to keep the fastener from corroding on the shelf and pretty for a little while. Don’t you think a fastener that’s been on the market for over 40 years would have corrected any problems with the plating (coating) by this time.
In the real world realm of maintenance the problems of proper fastener selection is, has, and will always be there. It is even more so that today, in that the skill level of the average maintenance worker is much lower than yesterday.
It is quite common in this area to specify a minimum grade of bolt for the site standard. I know of companies that have grade 5 and some that use grade 8 as the standard and some as I mentioned in the previous post using Supertanium or others. I will admit that this adds a little cost to the budget but will payback inkind if one incident is avoided. This is especially true if there is an injury.
The question about the requirements of preloading a fastener. If you preload (tighten} a fasteners beyond any working load it will encounter in service you should have no problems whether you are at the full capabilities of the fastener or not. I had rather have an overkill than be 10% under what’s required in the clamping force needed. If you will notice that the head of the Supertanium fastener is higher which in itself enables higher torque without the problem with a wrench slipping or caming off especially the open end or adjustable. At one time mechanics wouldn’t consider using the above wrenches, probably not for the fasteners sake, but the danger of busting a knuckle or falling on one's butt.
It is extremely hard to calculate every clamping force needed in a large industrial enviroment where a lot of mechanical devices are concerned. A mechanic should never be put in position to make a decision whether or not to use a grade 5 instead of a grade 8 or a 8.8 instead of a 10.9 at 2:00 on Saturday night.
The requirements for hydrogen relief for the aircraft industry are several times more stringent than for commercial fastenrs. They also have much better control of their operation environment than most commercial users.
The vast majority of field failed fasteners that I have examined over the years have failed for two reasons: hydrogen cracking (either embrittlement or stress corrosion) and fatigue (inadeqaute preload in almost all cases).
The best way to prevent hydrogen assisted failures to a minimum is to keep the fastener hardness as low as possible. Anything above Rc 40 is asking for problems.
I don't have a problem with Supertainium, I have a problem with high hardness bolts used in general purpose applications where the users don't have a full understanding of the service environment. The reason that the PC 12.9 is no longer listed in the SAE standards is because of the large number of hydrogen cracking issues that occured in the late '70s. The car companies have found that PC 10.9 (grade 8)gives them all of the load capability that is needed for their vehicles.
A hydrogen failure is "sudden, unexpected, catastrophic failure of the part". When you have had brake attachment bolts fail after five years in service from Stress Corrosion Cracking (from raod salt), you tend to get more conservative.
klyde,
Regardless of the ongoing discussion on this thread and the current situation in fastener industry picking a named fastener such as Supertanium, S.P.S. or other is a good move. The added expense is worth it. The procurement of quality fasteners is a big problem at the present and no relief is in site. As I’ve stated I had rather have an overkill than come under what’s needed.
Screwman
12.9 fasteners are being purchased and used everyday. The hardness at 34 Rc is below the accepted onset of H2 induced problems with the materials.
The 12.9 fastener was probably dropped due availability problems and as you state grade 8 material translate to 10.9. We have a piece of equipment that called out 14.9 SHCS.
This brings up another point concerning inservice fastener failure.
It has been my experience primary failure mode of fasteners in service to be fatigue. The fatigue failures had many sources, manufacturing defects, improper material, improper tightening and several others.
Our biggest lost from a fastener failure came from a manufacturing defect, under head die mark due to die misalignment, when forming the head. These fasteners were made by the dean of industrial fastener manufactureres at the time. The same fastener was used at Indy that year and they had 10 or so engine failures before the first 50 miles into the race.
If you need to use plated fasteners the problems induced by the plating can be overcome by the manufacturer by judicious quality control.
Here some guidelines we used if a plated fastener is needed, somewhat old but I think still viable.
@ 160,000 psi or below no problem.
@ 160,000 -220,000 psi H can be detrimental but if proper cleaning, plating and bakeout are used, no problem
@ 220,000 psi and above everything is special, mechanical cleaning, low embrittlement baths, and very long bakeouts and few others like VPD.
Even though, as you state, aerospace fasteners command a better reputation there have been some classic failures of same. The biggest one was on the Apache Helicopter. Another big item was the suspension bolts on the Humvee. And a lot more than we know about.
It has also been my experience that no matter the origin of a fastener, if it is to be used in a critical application some sort of quality assurance should be in place, if nothing more that a simple hardness test.
Property class 12.9 was removed from SAE standards because of hydrogen embrittlement problems. Post-plating de-embrittlement heat treatment is not a cure-all. For example, corrosion of a screw during vehicle use can generate sufficient hydrogen to cause delayed fracture. I agree with [blue]Screwman[/blue], use of electroplated zinc (with or without chromate conversion coatings) on high-strength fasteners is a recipe for disaster. New multi-layer zinc/organic coatings like those from Doerken, Magni, and Metal Coatings International are infinitely better considering performance (corrosion, torque/tension, hydrogen embrittlement resistance) and cost.
Regards,
Cory
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In the interest of not getting out some information that could be taken the wrong way by someone I will have to agree that on high strength fasteners plating has been, is, and will be detrimental to the service life of a said fastener. I also use the min Rc 34 instead of the mean of 39 Rc for the hardness of the 12.9 fastener.
I just think that a great majority of the problems with H and high strength fasteners could be traced by the metallurgical/mechanical/chemical history to a problem in manufacture. This not normally accomplished unless you have a single source for a particular fastener.
The problem is that in my years of investigating fastener failures I have only seen problems with Hydrogen, aside from very bad applications, when someone didn’t follow the appropriate specification or standard for the fastener. The failures that were directly attributably to Hydrogen damage were always traced to manufacturing deficiency especially when it came to the plating step in the fastener manufacture. Most of these problems came when the manufacturer of record for the fastener allowed control of the plating to get outside the fence. The plating process if not closely supervised can quickly come under the auspices of witchcraft and voodoo science.
The last Hydrogen problem with fasteners I had any dealings with was not caused by the plater but by the fastener supplier he acid cleaned some fasteners destined for use as high strength fasteners, not fully threaded, and there were problems while using the product in assembly.
CoryPad,
Just talked to an old colleague who now works for a very large supplier to the auto industry and get his slant on the delisting of the 12.9 fastener by SAE. With no hesitation he stated that it was cost driven. He also mentioned that there were other concerns like the proper torquing using existing tools, no need, and comingling of the fasteners. He also stated that they would have to add approximately 20% to the cost of a 10.9 or Grade 8 for a grade 12.9. He was very happy that it was dropped because it eliminated all his seperation problems with raw materials. But this just one opinion.
As we had over 200,000(H-11) high strength fasteners in servce the torquing/tightening is a problem. We used H-11
in places where they weren't needed (30%) due to possible misapplications of lower strength fasteners. We were driven to high strength fasteners due to increased pressures and we had no gasket worries, couldn't add bolt holes.
Yes we have some silver plated and each is in service for 5 years then replaced. We did try Gold , Ni, TiCd, Cd.
No problems with any plating over 30 years.
However, not all of the ISO property classes are used in these specifications for metric steel threaded fasteners. Specification SAE J1199, for example, no longer allows the high-hardness fasteners (ISO bolt classes 12.8 and 12.9), because these two classes are susceptible to delayed brittle fracture in corrosive environments. This change in SAE J1199 is in response to the stress-corrosion cracking of class 12.8 bolts in automobile rear suspensions after just 2 years of service in the Snow Belt of the United States (Ref 1).
...
Ref 1: T.J. Hughel, "Delayed Fracture of Class 12.8 Bolts in Automotive Rear Suspensions," SAE Technical Paper Series 820122, Society of Automotive Engineers, 1982
...
Caution: ISO bolt class 12.9 has also been removed from SAE J1199. Caution is advised when considering the use of class 12.9 bolts and screws because, like the 12.8 class, the 12.9 class is susceptible to stress-corrosion cracking. The capability of the bolt manufacturer, as well as the anticipated in-use environment, should be considered for both the 12.8 and 12.9 classes. High-strength products such as class 12.9 require rigid control of the heat-treating operations and careful monitoring of as-quenched hardness, surface discontinuities, depth of partial decarburization, and freedom from carburization. Some environments may cause stress-corrosion cracking of nonplated as well as electroplated products
There is no cost penalty for property class 12.9 fasteners due to composition (same as 10.9 except minimum carbon concentration is 0.28% vs. 0.20%) or heat treatment requirement (it has a lower tempering temperature than 10.9, so that should be a little cheaper). There may be higher costs to maintain control over decarburization, etc., but that shouldn't be near 20% of the parts' final cost.
Regards,
Cory
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CoryPad,
To me something doesn't jive here as the 10.9 and 12.9 fastener's hardness ranges overlap, which is understandable if, as you say, they are the essentially the same material only tempered differently. This means that both would have be Austenized under the same conditions so both 10.9 and 12.9 would be subject to the same degree of carb/decarb extremely bad for fatigue. The same atmosphere would be used for both and no problem . All the physical and metallurgical parameters you mention concerning high strength fasteners also must apply even to the lowly SAE Grade 5. Also any of the defects you mention are extremely detrimental to any fastener regardless of strength level.
Any reputable high strength fastener manufacturer should cover all the bases you mention. Nearly all the named premium fasteners, namely SHCS, approach the 180,000 psi tensile strength in actuality.
In this report was there any mention of failures of this nature on the gulf coast?
Do you have any idea of the preload on the failed fasteners?
What is the European position on the 12.9, as the design engineering profession still uses them?
“Delayed Fracture of Class 12.8 Bolts in Automotive Rear Suspensions" is not too informative on it’s own, does the report actually mention finding HE cracking was from corrosion or maybe something that happened in the mfg process and just delayed?
I’m going to try to get a copy of the report. I found another reference that says there is an actual picture of the fracture in the ASM Fractography Handbook. It will be interesting to see the fracture surface. Also in the article they are discussing 2 points in hardness which well within production testing on a good day.
There is one statement made in the following article says the chemical/ petroleum industry is blissfully unaware of the problem. I don’t know how blissful I am since I am well aware of the problems with the production of high strength fasteners, but not versed in the failure of same from atmospheric corrosion.
After checking all my reports, monthly reports, and my notes of things the only mention of failures in respect to hydrogen is from a process where the fasteners were exposed to HCL fumes.
One other interesting point is that this is about this time there was the great big push for Boron Steels as fasteners materials. Our foray into this mess cost us quite a bit of silver and gold and we had a lot of steel scrap for sale.
I have an email off the my manufacturing buddy and hopefully he will enlighten me on the cost differential.
Also I’ll get a quote on 10.9 vs 12.9 HHCS which may not mean anything under the present supply conditions.
Also there is manufacturing site near home that uses a tremendous amount of 12.9 fasteners in what is considered a corrosive enviroment. Since I recommend the plant Engineer for the job he should have some information available on the service life of his fasteners for his old buddy.
Corey,
I agree with you on the 12.9 failures in the late 70s. I was involved in the manufacturing end of that situation and the issue was if the cause was embrittlement related to mfg. or stress corrosion from the environment. Of course, there were some major differences of opinion about the root cause. In the end, the metallurgists determined that the failures were related to suseptable material (carbon alloy at a high hardness level with zinc plate) in an application that allowed salty water to pool around the head of the fasteners. Lowering the strength to 10.9 reduced the suseptability of the parts to SCC such that they were able to replace the in-service parts with new fasteners and eliminate the breakage.
Hydrogen failures are one of the more "interesting" issues in fasteners because the fracture surface looks the same if the hydrogen is manufacturing induced (embrittlement) or environmentally induced (SCC), the difference is primarily one of time duration.
The suseptabillity of parts to hydrogen cracking is a combination of a number of things but the three primary ones are the material properties (alloys and hardness), the applied stress and the environment. The suseptability of a material to SCC is related to the material property of the 'threshold stress intensity factor' (Kiscc) for the material. If the applied stress (tightening and service load) remains below the Kiscc threashold, there generally will not be hydrogen assisted failures. The Kiscc value is inversly proportional to the yield strength of the fastener (higher strength parts have lower threashold stress values).
Some examples: For a grade 8 (PC 10.9)(medium carbon alloy steel, Rc 33 - 39) with a yield of 130 ksi, the Kiscc is about 75. For a socket head cap screw (PC 12.9) (medium carbon alloy, Rc 39-45) with a yield of 150ksi, the Kiscc drops to 55. If you go up to a yield strength of 180ksi, the Kiscc drops to 30.
What all this means is that if you have high strength bolts in a corrosive service environment, you can safely load them to a decreasing proportion of their yield strength as their yield strength increase, without having dangers of SCC.
For a lot better description of all this, you can read the chapters on it in John Bickfords third edition of "Introduction to the Design & Behavior of Bolted Joints). Also look into any of a number of papers on the subject written by Lou Raymond (he has worked with the Navy on SCC issues related to submarine plates (ouch!) and has developed the ASTM rising step load test that quantifies Kiscc.
I feel a little like the guy who went to the fire hydrant to get a drink. I've got a lot more on me than in me. It seems that I've tapped a source of fastener kowledge and experience. BTW to "unclesyd": Korayvo Industrial Supply sent me data Resulting from tests conducted by Herron Testing Laboratories on 3/8-16 Hdw 6 suppliers. Of these Premier supplied the Supertanium and Lawson supplied Tru-Torq fasteners. The lab tests shows tensile strength differences of 222020 for Supertanium and 192430 for the Tru-Torq. Hardness was not given.
You guys have scared me into doing a more thorough analysis of my bolted structure. It is on the blade grips of an experimental helicopter that I have but did not design the bolted joint.
Thank you very much for the destroying my simple view of a bolted joint.
klyde,
We didn't start out to scare you and we also digressed from your original question.
I have to apologize for this but in the at the same time I’m glad we made you aware of the complexities of a bolt connection. If we had known this was a Jesus Nut type connection we would have been a little more direct in our replies concerning the type connection you have to achieve and what it would take to get you a safe, reliable, and sustainable joint. This gets complex as you have be able to assemble, tighten/preload, and lock it down. Phew!!
To quote an old saying: "Everything hangs on this connection". This was on the wall at the old NADP at Pensacola, Florida.
Please come back with a good description of your connection or a link to a picture of the helicopter, if possible the connection in question. If this is a kit, someone may have the answer offhand.
What does the helicopter manufacturer, if there is one, have to say or is this a one off machine?
Are you wanting to change fasteners because of a problem?
This information will help the respondents to offer some better directions, guidance, or get professional help.
Also if you know a mechanical engineer you might ask him for guidance or direction. If there is a flying club in your area they usually have people that have the expertise in this area and can point you down the correct path.
Good luck with your project and get back with us with any information or the successful first flight. Pleas tether the machine early on.
I don't think a carbon steel fastener is appropriate for an aerospace application like helicopter blade attachment. You should investigate alloy steels (e.g. 13-8, 17-4, 17-7, etc.), titanium alloys, or multi-phase alloys. Corrosion is inevitable for this application, and ultrahigh strength carbon steels are too susceptible to corrosion and hydrogen embrittlement.
[blue]unclesyd[/blue],
I just got the old SAE paper. I will read it today and post my comments.
Regards,
Cory
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SAE 820122 Delayed Fracture of Class 12.8 Bolts in Automotive Rear Suspensions
After over two years service in the "snow belt", class 12.8 bolts in GM "A" car rear suspensions began to fail, leading to the recall of 6.4 millions cars. Analysis of the failures showed that the cause was corrosion induced hydrogen assisted cracking.
On the basis of these findings, it was decided to recall all cars that might have 12.8 bolts in the rear lower control arms and replace them with class 10.9 bolts with washers under the heads. Concurrently, GM specifications covering 12.8 grade fasteners were discontinued.
Property class 12.8 was allowed under an Appendix for new materials. SAE followed GM and removed all property classes above 10.9, although I can't find documention yet.
Regards,
Cory
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unclesyd: I haven't fully shared the environment: I have 180hrs in the air with the helo. It has 5- 5/16-24 bolts marked Supertanium. The outer two bolts go thru a 1/8 thick 4130 steel strap on top and bottom, and the inboard 3 bolts go thru an additional 1/8 steel strap top and bottom. The blade butt is 2.25" thick and the blade is used on a number of helicopters such as an after market blade for the Rotorway Exec kit helicopter. No butt or blade failures to date. These blade straps then mount to the blade grips with 6-3/8-24 grade 8 bolts. The longest strap is 14" long.
I haven't heard of any corrosion showing up on other ships but?? To date we have had no bolt failures recorded. But as a retired engineer, the word Supertanium bothered me without some engineering data to support it. The thrust load (double shear)has been calculated at 20,358# at flight rpm. If I believe the Supertanium ultimate strength tests, they do provide an adequate safety margin on strength alone. Fatigue failures brought on by stress corrosion is another matter and I don't have numbers for that yet.
I will say that I darn sure appreciate the inputs I'm receiving in this forum. They are more thoughtfula and professional than any others that I've found.
Sorry to hit you with the hose, but you touched on a topic that Corey and I are really passionate about. We end up chasing issues like this and they drive us crazy. He and I have been involved in several of these from the supplier and user sides of things over the years and high hardness bolts and hydrogen failures are always scarey.
Thanks for sticking around through all of this.
For your applications, I would highly reccomend using aircraft quality bolts. They have the geometry, metalurgy and quality to stay together when someones life is involved. The folks at SPS have a pretty good fastener selector on their web site.
Use this and then get in touch with some aerospace fastener distributors to get your parts.
For this application, make a visual inspection a regular part of your process and if you see any signs of corrosion on the bolts I would replace them. It is cheap insurance for parts like this.
klyde,
Evidently the designer of the connection wanted a very strong bolted connection at this point or had problems and went to the Supertanium fastener for the added strength he needed. I would not come under the nominal accepted strength values, not actual, used with the Supertanium bolt. Stay at or slightly above this value for any replacement fastener you may use if a replacement is needed.
One other point to remember is that a aircraft quality fastener, depending on the material, is subject to the same problems as the Supertanium. The only thing is that Aircraft quality carries the paper work to verify that no problems that would be detrimental to it's service life. Things like the proper material or blank/fastener has not been acid or alkaline cleaned, if plated it's from the right type bath and conditions, and properly baked out to remove Hydrogen. I agree that Hydrogen can cause problems with fasteners if given the right set of conditions at any point in time. I don't think it's a problem in you application using due judgment.
I still would query the manufacturer of the “Helo” for a little more information about the bolting if possible.
At the present time if a Grade 8 needs replacing make sure you get a branded fastener. There have been some problems with Grade 8's lately. I would never use run of the mill Grade 8 fasteners.
Here is another source of alloy fasteners that have a very good reputation and wide variety of high strength fasteners.
I’m still after a quote on the two materials 10.9 and 12.9 HHCS. One thing that I found out that 12.9 is standard for SHCS while 10.9 is a special. 8.8 is also available off the shelf. My initial quotes were all over the map due to delivery dates and material problems.
Still waiting my buddy in the fastener mfg. to return my call.
