System Engineering / Pressure Equipment
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Systems Engineering / Pressure Equipment

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Remaining lifetime assessment based on creep strain

   

Fig. 1
Permissible service life as per TRD 508 in cases involving single-axis component stress (cf. Siempelkamp, Melzer).

 

Description:
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.  

Failure cause:
Die über einen Zeitraum von 3 Jahren durchgeführten Kriechdehnungsmessungen bestätigten jedoch keine Kriechdehnung. Mittels Oberflächenprüfung wurden auch keine weiteren Anrisse gefunden. Man vermutete ein Problem der Rissdetektion und der Fertigung, nachdem die Nähte ursprünglich nicht sachgemäß beschliffen waren.

Remedy:
At each annual inspection, randomly selected weld seams are tested for incipient cracks.

Our services – your benefits:
Proof that the cracks were not caused by excessive creep stress confirmed the suitability of the design (prototype) and reduced subsequent testing and inspection expenditure. Longer test and inspection intervals are also envisaged.

Consulting services from:
TÜV SÜD Industrie Service GmbH