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Systems Engineering / Pressure Equipment

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PED Professional 6

Cases of Damage

Below, various cases involving damage are illustrated, causes described and solutions suggested.

 

Delayed fracture in galvanized bolts 

Grade 10.9 galvanized bolts installed in a steel supply bridge failed relatively soon after installation. The individual bolts fractured spontaneously. Macroscopic analysis showed only slight deformation at the fracture sites. 

Delayed fracture in galvanized bolts 

 

Corrosion damage to copper pipes 

Damage caused by leaks in the copper piping supplying cold drinking water in a residential building was the reason for preparing a court opinion. The piping diameter was 18 and/or 22 mm.  

Corrosion damage to copper pipes 

 

Corrosion damage to a wash basin mixer tap 

The mixer tap of a wash basin in a hotel room failed and caused water damage. The tap, to which drinking water satisfying the quality requirements of the drinking water regulation was supplied, had been in service for approximately one year. The tap was cleaned with commercial cleaning agents. 

Corrosion damage to a wash basin mixer tap 

 

Erosion-corrosion damage to the heat exchanger tubes of a steam superheater 

In a refinery, boiler feedwater is heated in an exhaust-heat boiler and the steam thus generated returned to the process via a steam superheater. The heat-exchanger tubes of the steam superheater had been damaged during operation to such an extent as to even cause bursting. 

Erosion-corrosion damage to the heat exchanger tubes of a steam superheater 

 

Damage due to frost 

Leaks have occurred on the 180º bends of a heat exchanger provided with cooling gills and having coiled cooling pipes (Fig. 1). Water was conveyed within the pipes and a cooling fluid was acting upon the outer face of the pipes. In the damaged area, the outer surfaces have shown corrosion damage. 

Damage due to frost 

 

Material damage through thermal shock stress 

Leakage was detected at the welding seam of a main-steam collector outlet. Metallographic analysis of the fracture surface identified thermal cycling as the cause of failure. However, neither manufacturer nor operator could provide an explanation.  

Material damage through thermal shock stress 

 

Natural-frequency piping vibrations 

In an austenitic control line for a main-steam valve of a power plant, a poorly executed welding seam began to leak after approx. three operating years. The plant had to be shut down as a result.  

Natural-frequency piping vibrations 

 

Weld seam optimization 

After some years of operation, cracks formed in the perpendicular longitudinal weld on the vertical column guides of a roller-guided rack feeder. 

Weld seam optimization 

 

Vibration reduction 

On a pleasure steamer, strong vibrations which passengers perceived as unpleasant occurred under certain conditions on the rear sun-deck benches. 

Vibration reduction 

 

Pitting corrosion 

Approximately two months after fitting, a gutter made of aluminum plate surrounding the foyer of a building was leaking at various locations (cf. Fig. 1), resulting in water intrusion into the entrance hall of the building. The foyer was provided with a grass cover on its roof structure.  

Pitting corrosion 

 

Damage caused by start/stop operation 

Large parts broke from the die-cast bearing rollers of a large, drum-type rotating drying stove for wood shavings. Operation had to be stopped and, at the same time, there was the risk of the cylinder-shaped stove falling onto the operating premises. 

Damage caused by start/stop operation 

 

Remaining lifetime assessment based on creep strain 

After two years of operation, cracks were detected on the circumferential welds of a combustion chamber for powdered coal. An even surface was restored by grinding and operation was resumed. As creep cracking could not be ruled out as the failure cause, creep strain measurements were performed. 

Remaining lifetime assessment based on creep strain 

 

Defects in material 

Rectangular copper profile sections are welded together and formed to rings having various different radii. In these processing steps, brittle fractures will occur within the heat affected zone of the weld seams (Fig. 1).  

Defects in material 

 

Defects in welding 

Rectangular copper profile sections are welded together and formed to rings having various different radii. In these processing steps, brittle fractures will occur within the heat affected zone of the weld seams (Fig. 1).  

Defects in welding 

 

Vibration fatigue failures on a compressed gas bottle  

Premature cracks have occurred in alternating load tests on a compressed natural gas bottle used as fuel tank for a motor vehicle, in the area of the cylindrical shell.  

Vibration fatigue failures on a compressed gas bottle  

 

Stress/strain reduction 

Stress/strain reduction by modifying design or mode of operation 

Stress/strain reduction 

 

Tank vehicle with strain gauge measuring points 

To reduce dead weight and/or increase payload, strain gauge measurements were to provide experimental evidence of sufficient and safe tank-vehicle dimensions. 

Tank vehicle with strain gauge measuring points 

 

Fatigue failure at the welds of nested tubes 

An already existing municipal heating and power station was supplemented by a water-tube boiler fueled with natural gas and light oil. After only 28 hours of operation, fatigue failure occurred at 2 welds of the nested tubes of a new cylindrical boiler shell.  

Fatigue failure at the welds of nested tubes 

 

Laugeninduzierte Spannungsrisskorrosion 

In einer mit Dampf beaufschlagten Rohrleitung aus dem Werkstoff St 35.8 III sind während des Betriebes Risse quer zu Rundschweißnähten aufgetreten (Abb. 1). Die Überprüfung der chemischen Zusammensetzung der Rohrleitungswerkstoffe und des Schweißgutes ergab keine Hinweise auf die Schadensursache. 

Laugeninduzierte Spannungsrisskorrosion 

 

Zahnriemenscheibe eines Kraftfahrzeuges 

Die Zahnriemenscheibe eines Kraftfahrzeuges versagte, wobei ein Segment der Riemenscheiben aus dem Bauteil ausgebrochen ist. 

Zahnriemenscheibe eines Kraftfahrzeuges 

 

Autositzbefestigung: Schaden an einem Bauteil 

Im Versuch (Crash Test) versagte ein aus ferritischem Werkstoff kaltgebogenes Bauteil, das zur Befestigung von Autositzen eingesetzt wird. Das Bauteil hat bei vorangegangenen gleichen Versuchen den jeweils dabei aufgetretenen Beanspruchungen standgehalten. 

Autositzbefestigung: Schaden an einem Bauteil