QANTAS A380 Uncontained failure.
Join Date: Dec 2010
Location: S 51 N
Age: 84
Posts: 196
Likes: 0
Received 0 Likes
on
0 Posts
Although itīs "silent boat" in this thread since 5 days Iīd rather like to "bang" the door one more time. We have worked through the case fairly well, I think. However, why do we stop close to the point where "Pandoras Box" is pulled open ? I like to refer to Turbine Dīs list posted in Nr. 1888
Quote:
One way to look at it is this way: (A) leads to (B), (B) leads to (C), (C) leads to (D) and (E) leads to failure. This is the classical failure methodology of a complex system. Looking at engine #2's failure,
(A) = Unknown
(B) = Unknown
(C) = Unknown
(D) = Stub pipe
(E) = IPT Disc burst/major engine failure/damage to aircraft
The trick is to identify (C), (B) and (A), (A) being the root cause.[/quote]
Rolling down that list reversal way Iīd like to start at
(E) : IPT Disc burst/major engine failure/damage to the aircraft - symptom caused by "D" through "A"
(D) : Stub pipe fracture /oil spill - probable contributional cause ? sympton
caused by "B" or "C" or "A" ??
(C) : vibration - light on LP and IP shaft, severe on HP shaft - sympton caused
by "B" or "A" ??
(B) : rising oil temperature, wear of bearing ?? - sympton caused by "A" ?????
(A) : the real start and cause of the desaster, this one triggered all the other
recorded events.
I believe there is something technically that I can not cover with my knowledge about sophisticated jet engines, but that engineers might know of. There fore this as my last try to get a logical answer to what went wrong in that Qantas engine.
Quote:
One way to look at it is this way: (A) leads to (B), (B) leads to (C), (C) leads to (D) and (E) leads to failure. This is the classical failure methodology of a complex system. Looking at engine #2's failure,
(A) = Unknown
(B) = Unknown
(C) = Unknown
(D) = Stub pipe
(E) = IPT Disc burst/major engine failure/damage to aircraft
The trick is to identify (C), (B) and (A), (A) being the root cause.[/quote]
Rolling down that list reversal way Iīd like to start at
(E) : IPT Disc burst/major engine failure/damage to the aircraft - symptom caused by "D" through "A"
(D) : Stub pipe fracture /oil spill - probable contributional cause ? sympton
caused by "B" or "C" or "A" ??
(C) : vibration - light on LP and IP shaft, severe on HP shaft - sympton caused
by "B" or "A" ??
(B) : rising oil temperature, wear of bearing ?? - sympton caused by "A" ?????
(A) : the real start and cause of the desaster, this one triggered all the other
recorded events.
I believe there is something technically that I can not cover with my knowledge about sophisticated jet engines, but that engineers might know of. There fore this as my last try to get a logical answer to what went wrong in that Qantas engine.
A is caused by the design of the T-900. Too many bearings too close together.
Yes, we will not rest until RR goes in and removes one of those bearings ... their pick of which one
Join Date: Dec 2010
Location: S 51 N
Age: 84
Posts: 196
Likes: 0
Received 0 Likes
on
0 Posts
bearing ??
Smilin_ Ed, I doubt that there are less bearings in the T 1000 than in any previous 3 shaft engine.
If you want to check, this link gives access to all the big engines
Large aircraft engines - Rolls-Royce
lomopaseo, how sure can one be that a simple switch to a stronger bearing - or several - will solve the obviously existing problem ??
Do you think itīs just bearing ??
If you want to check, this link gives access to all the big engines
Large aircraft engines - Rolls-Royce
lomopaseo, how sure can one be that a simple switch to a stronger bearing - or several - will solve the obviously existing problem ??
Do you think itīs just bearing ??
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes
on
0 Posts
Trent 900 Compared To GP7200
Annex14
Here are the cutaway views of the two engines. Although one cannot see the details clearly, the general engine layout and differences can be seen. To see the actual details, one has to view the engine and see all the parts laid out on tables.
http://www.pw.utc.com/StaticFiles/Pr...taway_high.jpg
http://www.rolls-royce.com/Images/br...cm92-11346.pdf
Several things strike me: If there is any scale at all between the artistic renditions, the thrust ball bearings in the GP7200 look larger than those in the Trent 900. In the turbine area of the GP7200, the emphasis on slowing a speeding turbine rotor can be seen on both rotors where there would be blade on vane contact, there is no spacing concerns. The stage two turbine rotor (similar to the IPT rotor of the Trent 900) sits close to the structural frame behind it and the blade would contact the struts if this turbine disc were to move back.
Both engines deliver the same thrust, both have the same fan diameter, both have 14 compressor stages, the GP7200 has 6 LPT stages verses 5 for the Trent 900. The GP7200 is slightly longer and weighs 956 lbs. more. It has been reported the GP7200 has a 1% better SFC than the Trent 900, but RR disputes this. Both engines appear to be capable of being mounted on a common designed pylon. The maximum HP spool speed of the GP7200 is slightly higher than the Trent 900, but the maximum fan speed is lower on the GP7200.
For those wondering why the Trent 800 couldn't be used, you can't just clip 5" off the fan without rebalancing the rest of the engine, especially if you are being pressed on SFC to meet aircraft range goals. So two things happened on both engines, incorporation of 3-D highly aerodynamic efficient swept fans, higher HP spool speeds, higher pressures and temperatures, all to generate thrust requirements and deliver good SFC.
I do wonder if the counter-rotational feature (new to a commercial high by-pass engine) had any effects on bearings, frequencies or vibration in the Trent 900.
Here are the cutaway views of the two engines. Although one cannot see the details clearly, the general engine layout and differences can be seen. To see the actual details, one has to view the engine and see all the parts laid out on tables.
http://www.pw.utc.com/StaticFiles/Pr...taway_high.jpg
http://www.rolls-royce.com/Images/br...cm92-11346.pdf
Several things strike me: If there is any scale at all between the artistic renditions, the thrust ball bearings in the GP7200 look larger than those in the Trent 900. In the turbine area of the GP7200, the emphasis on slowing a speeding turbine rotor can be seen on both rotors where there would be blade on vane contact, there is no spacing concerns. The stage two turbine rotor (similar to the IPT rotor of the Trent 900) sits close to the structural frame behind it and the blade would contact the struts if this turbine disc were to move back.
Both engines deliver the same thrust, both have the same fan diameter, both have 14 compressor stages, the GP7200 has 6 LPT stages verses 5 for the Trent 900. The GP7200 is slightly longer and weighs 956 lbs. more. It has been reported the GP7200 has a 1% better SFC than the Trent 900, but RR disputes this. Both engines appear to be capable of being mounted on a common designed pylon. The maximum HP spool speed of the GP7200 is slightly higher than the Trent 900, but the maximum fan speed is lower on the GP7200.
For those wondering why the Trent 800 couldn't be used, you can't just clip 5" off the fan without rebalancing the rest of the engine, especially if you are being pressed on SFC to meet aircraft range goals. So two things happened on both engines, incorporation of 3-D highly aerodynamic efficient swept fans, higher HP spool speeds, higher pressures and temperatures, all to generate thrust requirements and deliver good SFC.
I do wonder if the counter-rotational feature (new to a commercial high by-pass engine) had any effects on bearings, frequencies or vibration in the Trent 900.
Join Date: Jul 2005
Location: OZ
Posts: 580
Likes: 0
Received 0 Likes
on
0 Posts
I enjoy this thread as it is filled with useful info.
To add to Turbine D input
The GP7200 ball thrust bearing carries greater radial loads as well as thrust loads where the T900 has a large roller brg to carry the radial loads with the thrust loads transferred to location bearing adjacent the engine mount. Roller bearings typically have higher load capacity than ball bearings for a given size.
The GP7200 has had its fair share of problems, Fan balance issues that have cracked airframe structure and lowered engine mounted accesories life spans. This has generated huge manhour costs and extended ground times but to date has not exploded mid-air. GP7200 1 , RR nil
I see your point except the T800 was a known off the shelf product, now very reliable with the thrust avail to do whats asked plus more. So why the T900 when it requires greater SFC to offset its greater weight before it offers any greater efficiency to the aircraft. So at a glance it does not add up unless huge future promises (SFC) were attached to the T900 model that could not be acheived from current models ?
This is true but RR have been building a contra rotating core for the harrier since the 1960s so I would not call it new to RR and the location IP bearing that supports the fan location bearing turns in the same direction i.e. the ball race speeds have not been a marked increase. This bearing design has been a thorn in RR side since the conception of the RB211 but again is not new technology.
I suspect we will find out once the hype has died down and RR PR machine have massaged and cajoled its customers to accept a modified core engine at a lowered price with the guarantees of increased efficiency ?? (read reliability)
The money will have to come from somewhere and I suspect it will be shared across RR EADS and customers all of whom have committed so much can not afford this to fail. Time will tell.
To add to Turbine D input
Several things strike me: If there is any scale at all between the artistic renditions, the thrust ball bearings in the GP7200 look larger than those in the Trent 900
Both engines deliver the same thrust, both have the same fan diameter, both have 14 compressor stages, the GP7200 has 6 LPT stages verses 5 for the Trent 900. The GP7200 is slightly longer and weighs 956 lbs. more. It has been reported the GP7200 has a 1% better SFC than the Trent 900,
For those wondering why the Trent 800 couldn't be used, you can't just clip 5" off the fan without rebalancing the rest of the engine, especially if you are being pressed on SFC to meet aircraft range goals. So two things happened on both engines, incorporation of 3-D highly aerodynamic efficient swept fans, higher HP spool speeds, higher pressures and temperatures, all to generate thrust requirements and deliver good SFC.
...--------...Thust...Weight .Thrust to weight...Length.. Fan Dia..Serv Enrty
Trent 892 - 92,000...13,100....---....7.0 ......... 172 .... 110...... 1997
Trent 972 - 76,752...13,842....---....5.5 ......... 179 .... 116...... 2006
Trent 892 - 92,000...13,100....---....7.0 ......... 172 .... 110...... 1997
Trent 972 - 76,752...13,842....---....5.5 ......... 179 .... 116...... 2006
I do wonder if the counter-rotational feature (new to a commercial high by-pass engine) had any effects on bearings, frequencies or vibration in the Trent 900.
I suspect we will find out once the hype has died down and RR PR machine have massaged and cajoled its customers to accept a modified core engine at a lowered price with the guarantees of increased efficiency ?? (read reliability)
The money will have to come from somewhere and I suspect it will be shared across RR EADS and customers all of whom have committed so much can not afford this to fail. Time will tell.
Join Date: Dec 2010
Location: S 51 N
Age: 84
Posts: 196
Likes: 0
Received 0 Likes
on
0 Posts
Turbine D - Bolty McBolt
Once again a very helpful explanation to a layman in jet engine technology.
Especially I like the comparison of GP 7200 and Trent 900. Within a glance it is clear that the construction of those elements that carry the dynamic loads are much lesser concentrated on one small area in the GP 7200 than in the Trent 900. Wether that has a real influence on the problems we have seen on the QF - Trent I only can imagine / assume. But if this problem exists for so many years - Bolty McBolt says since the beginning of the RB 211 - and the production of that type engines goes on with now and than a "big bang" one must ask the question wether there has been ever an in depth investigation towards possible harmonics???
I remember that there have been aircraft desighns that used a long driving shaft for the propeller. Few of these even had counterrotating props. Some of the types ran into kind of severe shaft failures - as far as I remember - caused by kind of harmonics or resonant frequencies ?? I may be corrected at this, too long ago. Doesnīt know if this is applicable in now a days desighn technologies. But what if, . . . . . the counterrotating HP component generates a harmonics that is transferred via bearings the different shafts to other parts of the engine ?? Is that thinkable ?? I must admit, my confidence in RR - engineers abilities exclude such a scenario.
Again I have to cry for help by the engineers !!
DERG
Is that yellow marking just a gag or is it true ??. I have seen some Harriers - must admit on fly by - but havnīt seen something like that. But I can imagine that it might have been indeed a measure of caution.
Jo
Once again a very helpful explanation to a layman in jet engine technology.
Especially I like the comparison of GP 7200 and Trent 900. Within a glance it is clear that the construction of those elements that carry the dynamic loads are much lesser concentrated on one small area in the GP 7200 than in the Trent 900. Wether that has a real influence on the problems we have seen on the QF - Trent I only can imagine / assume. But if this problem exists for so many years - Bolty McBolt says since the beginning of the RB 211 - and the production of that type engines goes on with now and than a "big bang" one must ask the question wether there has been ever an in depth investigation towards possible harmonics???
I remember that there have been aircraft desighns that used a long driving shaft for the propeller. Few of these even had counterrotating props. Some of the types ran into kind of severe shaft failures - as far as I remember - caused by kind of harmonics or resonant frequencies ?? I may be corrected at this, too long ago. Doesnīt know if this is applicable in now a days desighn technologies. But what if, . . . . . the counterrotating HP component generates a harmonics that is transferred via bearings the different shafts to other parts of the engine ?? Is that thinkable ?? I must admit, my confidence in RR - engineers abilities exclude such a scenario.
Again I have to cry for help by the engineers !!
DERG
Is that yellow marking just a gag or is it true ??. I have seen some Harriers - must admit on fly by - but havnīt seen something like that. But I can imagine that it might have been indeed a measure of caution.
Jo
Join Date: Jul 2009
Location: EPWA
Age: 65
Posts: 86
Likes: 0
Received 0 Likes
on
0 Posts
there is also another difference concerning spline location
in GP the spline is located directly 'inside' bearing and in T900 the IP spline is 'outside' of the bearing plane. The difference becomes significant under dynamic load when any radial forces and radial play comes into account.
in GP the spline is located directly 'inside' bearing and in T900 the IP spline is 'outside' of the bearing plane. The difference becomes significant under dynamic load when any radial forces and radial play comes into account.
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes
on
0 Posts
Loving the discussion (despite a lot of it going over my head), shame about the RR-bashing though.
I remember that there have been aircraft desighns that used a long driving shaft for the propeller. Few of these even had counterrotating props. Some of the types ran into kind of severe shaft failures - as far as I remember - caused by kind of harmonics or resonant frequencies ?? I may be corrected at this,
The problem comes in when operation is either abnormal (damaged parts creating unbalance or aerodynamic burbles) or parts which have lower than expected fatigue margin due to manufacturing flaws. And one of the largest corntributors have been misassembled parts which seriously affect the stiffness of joints between parts.
Nothing that RR doesn't already know and adresses
Join Date: Dec 2010
Location: S 51 N
Age: 84
Posts: 196
Likes: 0
Received 0 Likes
on
0 Posts
Thanks thats sure a brief but helpful explanation. As I expressed already, would be hard to understand if the RR engineers had not addressed that problem properly.
Yet, we are chewing on that cause (A) - the root cause.
Jo
Yet, we are chewing on that cause (A) - the root cause.
Jo
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes
on
0 Posts
Bolty McBolt
In my previous post, I erred on the clipped fan and re-balancing scenario. Actually, I should have been referring to the GE90, not the Trent 800. The core of the GP7200 engine comes via the GE90 core. So when the fan diameter was reduced to 116" from the normal ~123" diameter fan used on the GE90, some other things had to be adjusted. The GE90 core evolved out of the "Energy Efficient Engine". A scaled GE90 engine was built to test the concept from which the true GE90 emerged. So GE had good knowledge as to how to scale downward the core to match fan diameter. In fact, the GEnx engine basically uses the scaled GE90 core.
I just think the drive for both the Trent 900 and GP7200 engines was to improve specific fuel consumption (SFC). If you look at the CF6-80C2, the model used on the B-747-400, The sea level SFC is 0.316, at cruise it is 0.605.
If you look at the Trent 800 on the B-777, the sea level SFC is 0.35, at cruise it is 0.56.
If you look at the GE90 on the B-777, the sea level SFC is 0.324, at cruise it is 0.52.
It is estimated the GEnx on the B-747-8, the sea level SFC is 0.27, no figures yet for cruise.
Theere are no SFC published figures out yet for the Trent 900 or the GP7200 engines, except for the comments from the Emirates CEO.
So with the trend of less fuel usage (improved engine efficiency), IMO, the Trent 900 and GP7200 fits somewhere nearer to the GEnx.
In my previous post, I erred on the clipped fan and re-balancing scenario. Actually, I should have been referring to the GE90, not the Trent 800. The core of the GP7200 engine comes via the GE90 core. So when the fan diameter was reduced to 116" from the normal ~123" diameter fan used on the GE90, some other things had to be adjusted. The GE90 core evolved out of the "Energy Efficient Engine". A scaled GE90 engine was built to test the concept from which the true GE90 emerged. So GE had good knowledge as to how to scale downward the core to match fan diameter. In fact, the GEnx engine basically uses the scaled GE90 core.
I just think the drive for both the Trent 900 and GP7200 engines was to improve specific fuel consumption (SFC). If you look at the CF6-80C2, the model used on the B-747-400, The sea level SFC is 0.316, at cruise it is 0.605.
If you look at the Trent 800 on the B-777, the sea level SFC is 0.35, at cruise it is 0.56.
If you look at the GE90 on the B-777, the sea level SFC is 0.324, at cruise it is 0.52.
It is estimated the GEnx on the B-747-8, the sea level SFC is 0.27, no figures yet for cruise.
Theere are no SFC published figures out yet for the Trent 900 or the GP7200 engines, except for the comments from the Emirates CEO.
So with the trend of less fuel usage (improved engine efficiency), IMO, the Trent 900 and GP7200 fits somewhere nearer to the GEnx.
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes
on
0 Posts
Qantas A380 & B747 News
Join Date: Apr 2008
Location: WA
Age: 84
Posts: 23
Likes: 0
Received 0 Likes
on
0 Posts
Turbine D - DERG
I've been following with great interest the discussion in this thread relative to the several failure scenarios that have been set forth re: Qantas T900 uncontained IPT failure. Back in the conversation (#'s 221 and 223) you briefly brought up the topic of oil and possible coking problems during heat soaking. There was a brief suggestion that inclusion of an external oil circulator unit would have been a sensible part of the overall design for longevity.
Could you discuss from your engineering standpoints, the possible or probable effects of short and long term coking on the actual performance of the hot section bearing(s) in this engine? I've been wondering if it's possible that bearing performance from coking could have degraded to the point where it may have overheated, chattered, and or vibrated itself to the extent that it either partially or even totally disintegrated, whilst also impacting the stub pipe. What I'm asking is, is it possible the bearing itself was causal in the sequence of events ending in the IPT overspeed? Maybe I missed someone discussing this very event in an earlier part of the thread?
Failures of this type are not unknown, of course, in automotive and aircraft turbochargers. The simple solution has always been to, one way or another, make sure the shaft bearings are bathed in circulating oil after shut down. Even old dirty mineral oil is ok to stop most coking, just so long as it keeps coming. If this solution is found necessary for T900 bearings I'd almost bet that it could be done for far less penalty than a 50kg bolt-on accessory.
Thanks everybody for all your great contributions to this thread. What a wonderful resource this forum is.
I've been following with great interest the discussion in this thread relative to the several failure scenarios that have been set forth re: Qantas T900 uncontained IPT failure. Back in the conversation (#'s 221 and 223) you briefly brought up the topic of oil and possible coking problems during heat soaking. There was a brief suggestion that inclusion of an external oil circulator unit would have been a sensible part of the overall design for longevity.
Could you discuss from your engineering standpoints, the possible or probable effects of short and long term coking on the actual performance of the hot section bearing(s) in this engine? I've been wondering if it's possible that bearing performance from coking could have degraded to the point where it may have overheated, chattered, and or vibrated itself to the extent that it either partially or even totally disintegrated, whilst also impacting the stub pipe. What I'm asking is, is it possible the bearing itself was causal in the sequence of events ending in the IPT overspeed? Maybe I missed someone discussing this very event in an earlier part of the thread?
Failures of this type are not unknown, of course, in automotive and aircraft turbochargers. The simple solution has always been to, one way or another, make sure the shaft bearings are bathed in circulating oil after shut down. Even old dirty mineral oil is ok to stop most coking, just so long as it keeps coming. If this solution is found necessary for T900 bearings I'd almost bet that it could be done for far less penalty than a 50kg bolt-on accessory.
Thanks everybody for all your great contributions to this thread. What a wonderful resource this forum is.
Join Date: Dec 2010
Location: S 51 N
Age: 84
Posts: 196
Likes: 0
Received 0 Likes
on
0 Posts
Turbine D
Oh NO !!! Not another Trent engine smashed to pieces. Lucky enough this is a contained failure and it happened on the ground.
Guess, finally someone might have to start thinking !!!
Guess, finally someone might have to start thinking !!!
Join Date: Dec 2010
Location: S 51 N
Age: 84
Posts: 196
Likes: 0
Received 0 Likes
on
0 Posts
The oil coking problem in pipes was detected and explained on some earlier incidents with other type Trent engines. The pipes involved where bearing chamber vent pipes. It was anticipated in investigation that the coking blocked these pipes leading to heating and failure of the bearings.
It was also in the first segment of this thread once mentioned in conection with the QF 32 engine failure. I didnīt even know that oil coking could become a cause of problems in bearings. But I can see your point.
It was also in the first segment of this thread once mentioned in conection with the QF 32 engine failure. I didnīt even know that oil coking could become a cause of problems in bearings. But I can see your point.
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
The coking problem is genuine, and may be influenced by operational techniques.
Tactical aircraft oft perform rapid turnarounds, reloading/refueling as fast as possible. If the engine is shut down soon after high-power ops, and if the engine has an oil-fuel heat exchanger in the high-pressure fuel manifold, the hot oil works on the static fuel mass and may boil the fuel, inducing fuel vapor into the hot combustor, and causing a brief post-shutdown fire. Probably not harmful, because of brief duration, but likely exciting.
In the commercial world, a proper cooldown period is important to prevent coking, especially when T900 "normal" oil temps are as high as 180C. In thinking about A380 ops, since only inboards are equipped with reversers, they are likely to see hotter oil at shutdown than the outboards.
And so it is possible that something in QF shutdown timing technique is aggravating the coking problem. I suspect QF and R-R are already examining this issue.
Tactical aircraft oft perform rapid turnarounds, reloading/refueling as fast as possible. If the engine is shut down soon after high-power ops, and if the engine has an oil-fuel heat exchanger in the high-pressure fuel manifold, the hot oil works on the static fuel mass and may boil the fuel, inducing fuel vapor into the hot combustor, and causing a brief post-shutdown fire. Probably not harmful, because of brief duration, but likely exciting.
In the commercial world, a proper cooldown period is important to prevent coking, especially when T900 "normal" oil temps are as high as 180C. In thinking about A380 ops, since only inboards are equipped with reversers, they are likely to see hotter oil at shutdown than the outboards.
And so it is possible that something in QF shutdown timing technique is aggravating the coking problem. I suspect QF and R-R are already examining this issue.
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
DERG:
The two universal, perennial complaints of the engineering profession:
"To solve the problem, we need more data" - and:
"There's so much data, we need more time to analyze it all"
Of course it is also recorded for analysis later if needed. After this accident one senior mechanical engineer said: "we have an enormous amount of data, and it is going to take some time to plough through it"
"To solve the problem, we need more data" - and:
"There's so much data, we need more time to analyze it all"
Guest
Posts: n/a
DERG
Howdy. Rather than dredge up my old posts, I'll rephrase and update. The "Pipe" is NOT the victim of some inattentive Bench Monkey.
First, notice the "Land", or "Ledge" that supposedly resulted from a "counterbore" gone awry. Look closely at the "corner" enunciated at the transition from ledge to Wall.
It is COVED. It shows no sharp delineation twixt the bore and the "Shoulder". This is 100 per cent the result of wear, and given its locale, almost certainly caused by vibration.
Next, note the Striae on the wall of the inner surface of the "normal" pipe. My opinion is a pulled extrusion process assuredly excluding any secondary operation, or Blunder. Gently Helical signatures from a normal process of machining. Now, look at the area of the Pipe proxima; to the "ledge". There are circumferential grooves, the result of metal/metal wear, as this is undoubtedly the joint locus of two fittings. Look closely and see that the grooves are at bias to the ledge, and irregular, random even, and certainly not the result of any machining process.
There is a great deal more. Suffice that ATSB allowed for a wide open gate for later correction: "....MAY have initiated a sequence of failures that led to burst...."
Howdy. Rather than dredge up my old posts, I'll rephrase and update. The "Pipe" is NOT the victim of some inattentive Bench Monkey.
First, notice the "Land", or "Ledge" that supposedly resulted from a "counterbore" gone awry. Look closely at the "corner" enunciated at the transition from ledge to Wall.
It is COVED. It shows no sharp delineation twixt the bore and the "Shoulder". This is 100 per cent the result of wear, and given its locale, almost certainly caused by vibration.
Next, note the Striae on the wall of the inner surface of the "normal" pipe. My opinion is a pulled extrusion process assuredly excluding any secondary operation, or Blunder. Gently Helical signatures from a normal process of machining. Now, look at the area of the Pipe proxima; to the "ledge". There are circumferential grooves, the result of metal/metal wear, as this is undoubtedly the joint locus of two fittings. Look closely and see that the grooves are at bias to the ledge, and irregular, random even, and certainly not the result of any machining process.
There is a great deal more. Suffice that ATSB allowed for a wide open gate for later correction: "....MAY have initiated a sequence of failures that led to burst...."
Join Date: Jul 2007
Location: West Sussex
Age: 82
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
bear
I think you are incorrect in your suppositions, which do not seem to be shared by anyone else.
The 'cove' at the bottom of the incorrect counterbore is the runout radius of the counterbore tool. Radius at this position is essential to avoid a stress concentration factor. Careful design would never tolerate a sharp corner .
The 'bias' in the tooling marks is caused by the feeding in of the tool. It is a shallow angle helix determined by the feed rate of the cutter.
We are all ignorant as to the design surrounding this failed part, but it is probably the female element of an O ring seal. As such, gross frettage of the nature which you assume is unlikely.
Time to move on.
I think you are incorrect in your suppositions, which do not seem to be shared by anyone else.
The 'cove' at the bottom of the incorrect counterbore is the runout radius of the counterbore tool. Radius at this position is essential to avoid a stress concentration factor. Careful design would never tolerate a sharp corner .
The 'bias' in the tooling marks is caused by the feeding in of the tool. It is a shallow angle helix determined by the feed rate of the cutter.
We are all ignorant as to the design surrounding this failed part, but it is probably the female element of an O ring seal. As such, gross frettage of the nature which you assume is unlikely.
Time to move on.
