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Does really the turned-over concrete pump became a rack?!

Does really the turned-over concrete pump became a rack?!
During unexpected movement of a mobile concrete pump, the whole vehicle turned-over. As a result, the driver cabin had crashed and the main arm was expected to be damaged. According to concrete pump manufacturer experts – the pump became dangerous for use and was defined as total-loss, therefore the certificate of operation was cancelled.
A group of our engineers executed reverse engineering methodology on main arm in order to determine damage extent and to perform risk assessment of the system.
Work consisted of overhaul measurements,(since no drawings were available), establishment of computerized model of the arm by Ansys ™ software and then construction a dynamic model of the system by ADAMS™ software.
Geometry measurements and original geometry were compared (with Ansys ™) in order to simulate reconstruction of existing deformation. Fartheremore, original dynamics could be compared (with ADAMS™) with the "deformed" system dynamics. The results were - 1% change in lateral movement!
Based on the detailed analysis, the basic certificate of operation was re-issued, and no extreme repairs were needed, beyond some extra painting...
Indeed, the manufacturer build fantastic machines...


The location of main deformation

The location of main deformation
While lifting a 0.5 ton load of ceramic plates, in Northern Israel, a crane suddenly collapsed on a 12-story building.
Visual inspection at-site detected two unexpected fractured components- one wheel boogie and a boom element parallel to the 10 story level.
It was suspected that the failure of these items was caused by the presence of a preliminary crack within these components.
Laboratory geometric measurements of the components fracture zone did indicate local necking that implies of overload mechanism. Microscopic inspection using SEM validated the failure mechanism of these components to be a sudden overloading event.
In order to evaluate possible cause, using computerized models several scenarios were simulated. The following was the result of that analysis:

A. In the morning of the event, rough wind existed and drove the crane
on its rail until it reached the rail-end stoppers.
B. When reaching the stoppers the crane sprung backwards and one of
the wheels didn't return to its place on the rail.
C. Standing on three wheels only enabled a limited safe working zone for
the crane to work.
D. When exceeding that zone, the crane collapsed.

Corrosion in heat exchanger- improper inhibitor selection

Corrosion in heat exchanger- improper inhibitor selection
An overhaul procedure had been applied to a screw compressor system of 350 ton-cooling capacity. During that process all 76 elements of ½ “ tubes had been replaced within the system heat-exchanger. Three years later, leakage was detected at some of these tubes.
Operation procedure of the system included the use of anti-bacteria inhibition.
Damage to the tubes was characterized as pitting corrosion intermixed with large flakes and rust scale within the tubes. No abnormalities were obvious on tube outer surfaces. Inner surface damage was typical of active corrosion process resulted from corrosion aeration of surface due to the absence of any passive layer to protect the metal. Furthermore, review of inhibitor used within the system indicated that it is suitable for water hardness< 220 ppm and Alkalinity <30 ppm. Since in Israel water hardness is mush higher then 200 ppm; it is obvious that inhibition was improper and may, then, even harm the system.
As an action step the inhibitor was replaced and the leaking tubes were dismantled, only then the problem was so solved.

Longer arms of bulldozer – resulted in obvious cracks…

Longer arms of bulldozer – resulted in obvious cracks…
During regular earthmoving works within a strong noise of fracture was suddenly heard. The front arm of a large wheeled bulldozer fractured near the weld seam of the arm sleeve at the end counter to blade connection.
Examination of the second arm indicated immediately another crack at the exact same location, but yet still closed. Technical data concerning the system indicated that the specific bulldozer is long used without any abnormalities. Yet, the manufacturer developed, due to the customer requests, a set of arms longer then the original set in 1.5m’. No other construction changes were applied beyond that improvement. 6 such units had been sold in Israel. Except the one that fractured, all other 5 units suffered severe cracking phenomena at the same exact location – weld seam root. SEM inspection determined the failure mechanism to be Low Cycle Fatigue that originated from multipleorigins along arm counter walls. No metallurgical irregularities were detected within material including weld seam.
Final conclusion focused on mechanical issue to be the direct cause for failure. To be precise, we concluded that since the arms were longer then the originals, they should have been strengthened, what have not been done.
A month afterwards the bulldozer manufacturer replaced the main arms of all six machines without any extra-charge. Inspection of these arms verified local strengthening at the prior cracked zone.


More then 300 tractors sold- 25 are already defective...

More then 300 tractors sold- 25 are already defective...
During regular digging procedure a tractor has turn aside. Preliminary inspection on-situ detected one of the main arms broken. That tractor was considered a popular machine due to its cheap price and cheap maintenance costs. Yet, the scenario of “sudden” failure occurred more then once (to be precise we gathered 25 incidents…).
Laboratory inspection mapped the fracture and found that 30% of its path follows local welding seam of the arm.
Furthermore, microscopic survey of fracture indicated a multiple origin sector to be the initiation zone. Metallography did not detect any abnormalities, neither on metal base nor on welding seam. SEM inspection of fracture revealed fatigue striations to propagate from origin area of fracture up to 60% of wall width. While reaching that point, the crack achieved the critical size, and then fractures under abrupt overload.
These findings exclude any metallurgical irregularity to be the cause of failure and consider improper design of arm system to be the direct cause.


Extra sealant material beneath screw within bore

Extra sealant material beneath screw within bore
During a regular digging work an excavator hit an underground high voltage line. Short time after that collision the operator felt difficulties in machine steering. As a result the system was transferred to the garage for check-up. During dismantling a defect was detected at the main oil pump. Found also some chips within hydraulic oil filter, and a broken spacer of the pump.Some of the spacer screws were partly unscrewed, thus not fastening the spacer. Stereoscopic survey of the spacer fastening screws at the broken spacer sector revealed irregular fracture pattern, which was verified by SEM analysis to be high cycle fatigue fracture. While carefully cutting through the broken screw seat, unexpected view was exposed underneath (see photo)- extra ammount of sealant material fills the screw bore, undermines the compete fastening of the screw. That fiilup is associated with assembly stage of the pump.
These findings clearly implied of the following misup scenario - improper installation of the pump screws due to extra ammount of sealant material; partial fastening of screws; free to move spacer; disintegration of components upto complete failure.
It is claer, though, that neither the operator nor the high voltage line are responsible for that failure...

The thin (6 mm)reinforcment steel is exposed

The thin (6 mm)reinforcment steel is exposed
During a project acceptance phase, at a construction site, cracked concrete plates were discovered. The cracking phenomenon was detected at the bottom face of the plates on 90 units out of 150 units.
Nondestructive testing by radiography method was preformed in order to expose both setting and size of the reinforcing steel, inside the concrete plates. The inspection indicated a difference of 50% in the reinforcing steel diameter compared with the designed diameter. In simple words, the steel was half the diameter of what it should have been. Furthermore, the actual steel setting was different from the designed.
In order to verify the unexpected radiography results, a single plate was mechanically disintegrated - thus the diameter of the reinforcing steel was, indeed, 6 mm while the designed diameter was 12 mm.
As a result, all the plates in that site were replaced. Repair costs came to a value of $100,000.


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