the Institute of Failure Analysis

Typical crack at the bending area (X70)

Typical crack at the bending area (X70)

Customers that complained of an inner defect within the Electro-mechanic system returned a critical failed component. The system has been operating for 15 years, at various customers' premises without any problems, up to the last 2 years where problems arose. Checking back records, the manufacturer found that the only significant change done within the manufacturing process was changing the subcontractor that was conducting the gold plating of the part. The manufacturer naturally suspected that corrosion developed due to poor gold plating. Furthermore, he assumed that the corrosion was the reason for electrical disconnection.
20 part were dismantled, cut, chemically identified and examined metallurgically but corrosion products presence that were depicted could not explain the electrical disconnection.
SEM inspection revealed cracking and fracture phenomenon in the electrical wires.
It was detected that the manufacturer did not take into consideration sharp angles and bending of the electrical wires while stamping the wire plate. As a result prior to gold plating of the wires microcracks were already induced and later-on they developed into fractures.
The manufacturer checked both manufacturing procedure and tools and found that the stamping equipment used to create wire plate was damaged and created sharp angles and cracks.
The manufacturer then adjusted the equipment and redesigned the board's layout.

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.

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.

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...

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...

A view of a defective spring

A view of a defective spring
The last stage of house construction of Holmes family was the creation of very nice garden. The gardener work consisted of fertilizing the soil, establishing computerized irrigation system and planting trees & flowers. Several months later Holmes family intended to travel a broad and therefore, Mr. Holmes, programmed the irrigation system accordingly. When the family returned back from the vacation they were puzzled to discover that the garden was flooded and that all plants were damaged due to a defect at one of the irrigation units.
The Institute engineers, who found a small broken spring inside, inspected that unit. The spring dimensions included wire diameter of 1.4 mm, O.D –6mm and length – 50mm. Microscopic inspection revealed pits all over the spring wire, in addition to fracture zone. SEM/EDX analysis identified the material to conform to AISI 304, and on fracture surface residues containing Cl and Br were detected. The outcome of these tests is that the spring fractured due to pitting corrosion mechanism as a result of its exposure to aggressive materials. These materials brittled the spring and caused a fracture under regular operation conditions.
It is obvious, though, that the manufacture of the irrigation unit did not limit the use of it only for regular (tap) water (not containing any fertilizers) and, therefore, while using the units with fertilizers it initiated an accelerated corrosion attack.
Further to laboratory results the manufacturer called back the defective line of products.

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.

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