Banshee,

Here are several good examples of the H-11 steel fasteners being removed under mandate and otherwise:

From Aviation Today : Late last week the Federal Aviation Administration (FAA) issued an emergency airworthiness directive requiring Boeing [BA] B767 operators to inspect steel tension bolts on the struts attaching engines to the wings. Depending upon the aircraft production line number, operators have five days (through No. 162) and 10 days (through No. 230) to complete the inspections and report the results.

Boeing spokeswoman Liz Verdier was quoted in the May 19 New York Times saying that when the damage was found on the airplane that triggered the action (two bolts partly cracked, one bolt cracked completely through), the dismaying discovery "gave us a little bit of concern."

Boeing Model 767 Series Airplanes: emergency AD, requires a one-time inspection of the tension bolts in the side load underwing fittings on both struts to determine whether tension bolts made of H-11 steel are installed, in accordance with Boeing Alert Service Bulletin 767-57A0074, dated May 17, 2000, or Revision 1, dated May 18, 2000. If the inspection shows that no H-11 steel bolt is installed, no further action is required. If any H-11 steel bolt is found or if the type of bolt cannot be determined: prior to further flight, perform an ultrasonic inspection to detect cracking or fracturing of the tension bolts in the side load underwing fittings on both struts. If any cracked or fractured bolt is found, prior to further flight, replace both tension bolts in the affected side load underwing fitting with new, improved bolts. Effective May 18, 2000. AD 2000-10-51. Contact: James Rehrl, 425/227-2783; fax 425/227-1181.

COPYRIGHT 2000 Phillips Publishing International, Inc.
COPYRIGHT 2001 Gale Group


http://www.casa.gov.au/avreg/aircraf...7/B747-300.pdf


http://a257.g.akamaitech.net/7/257/2...f/03-21872.pdf

http://www.faa.gov/apa/pr/pr.cfm?id=1049 This one was issued from the FAA.

 

Don, I have a question on the torque settings. When we retorque after a month and are not using the ARP lube, should we use the 96lbs or 120 that arp says to use w/ engine oil? Will there still be enough of the moly on the treads to keep it to 96 lbs. I figure it will still be there in the nuts but if you back it off several turns will it not be engine oil on the threads then? Thanks Tim

 

Tim,

Use ARP lube everytime to TQ an ARP head stud. It is just more accurate. Do you still have some left?

Don~

 

No, between the initial install and the one hr retoque I have used it all. Might be a tiny amout I can squeeze out but not enough to do all 26 again. Tim

 

Chances are pretty good I have some here

Don~

 

Don,

Do you notice a common theme in those reports? I'll give you a hint, it's Boeing. After having seen some of the stuff they do those reports actually don't surprise me... LOL. Since you say they suffered from stress corrosion cracking that tells me they weren't relieved properly. If the fasteners are manufactured & processed correctly then the corrosion issues disappear. It's funny that those issues don't show up on H-11 fasteners on the Harriers downstairs from me... probably because their processed properly. ANY high strength steel can fail this way... including the ARP materials. If you'll take some time and read their website you'll see that they use these methods I'm talking about (primarily baking after coating) to eliminate the issue. THAT is why it's not a problem, not "because the material won't corrode".

On the clamp load, if it was 120 with moly lube with 190 psi... it's right on top of the yield curve... just like I stated before. I'm not aware that not ARP studs came with ARP lube... never bought a set myself. I used oil as a lube since it's probably what is used by most people. I'm sure some even put 'em in dry. The required torque to get the correct clamp is highly dependent upon the lube of the thread and nut/base mating surface.

 

Merrick and your Dad both had ARP lube in their kits. Merrick was instructed to TQ them to 125 ft lbs with ARP lube.

IMO , no fastener should be cranked up to the limit or past the limit of 88% yield in this application. What say you?

What yield do you think is being obtained at 120 ft lbs? You wrote: "right on the line" but could this actually be close to a failure point?

Don~

 

Doesn't Merrick have 14s now? I thought he did. If they are 12s then 131 is too much.

Max yield and failure are two different things. You do know what a stress-strain curve looks like, right? That 120 with lube puts the point right at the end of the yield curve, or the start of the plastic region. In other words, up to 100%, any stretch that the bolts takes on during torquing goes away once you remove it. If you go into the plastic region, plastically deform the bolt, and then remove the load, then the bolt will be permanently stretched a certain amount. Once the load is removed the bolt also takes on a permanent compressive stress. This compressive stress is actually very beneficial in the fatigue life arena. According to a retired Grumman engineer I had a class from a while back, the F-14 has areas of its airframe that are prestressed in this way to gain fatigue life. The yield point (that's the point at the top of yield curve) is still a long way from breakage. The bolt will continue to stretch with very little clamp load addition until it "falls off" and goes to failure.

 

Don:

Not trying to "beat a dead horse" here, but as I posted
earlier those 12mm studs went 120,000 miles on my 96'
with absolutely no head problems at all! IMO,.....
everything must have been right for that to happen.
Obviously the torque recommendations were right
or something surely would have happened especially
considering the high boost I had with the B-1 Turbos.
If you are going to be @ Muncie I would like to get
together with you and let you look at how nice those
12mm studs look after having been in the engine that
long. I will bring them with me! Are you planning on
being at Muncie Don??

Thanks.

---------
John_P

 

Banshee,


I am asking specifically, if in your opinion, the studs are overtorqued at 120 ft lbs using ARP lube. Would you recommend this TQ level over ARP's specs as a engineer to a customer?

Don~

 

How about them bengals? best football team in the nation
Just kiddin
DM01

 

Thanks for keeping this civil guys.
So far, its been filled with legitimate questions and informative answers.

Thanks
Rich.

 

The more permanent the connection, the higher you go towards yield point. I generally calculate at 90% for permanent, so that would be in the 110 range if I was recommending. However, being that I like tight bolts, I'd go for the clamp load of 120 before slacking back to 96

 

Rich:

I think this has been an excellent thread on the discussion
of head studs, pros, cons along with ALOT of technical
information mainly from "Don M" and "banshee."

I think it qualifies for a "five star" rating from you guys.
What do you think???

Thanks Rich!

---------
John_P

 

Indeed, this is a good technical thread.
I commend you guys for keeping it clean and informative. The essence of what DTR is all about.

Rich.