Fig. 1
Gilled radiator heat exchanger leaking in the area of the 180°-bend
Fig. 2 Magnification = 400
The fracture surface shows a honeycomb structure, character-istic feature of a ductile forced fracture
Fig. 3 Magnification = 100
The micro-section shows the typical structure of a ductile fracture

Description:
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.  

Failure cause:
Die fraktographischen und metallographischen Untersuchungen haben ergeben, dass zähe Gewaltbrüche Ursache der Undichtigkeiten sind (Abb. 2, 3). Die metallurgischen Eigenschaften des Bogenmaterials sind nicht zu beanstanden. Wegen einer System-Druckbegrenzung auf max. 3 bar Betriebsdruck können Steigerungen des Innendruckes nur mit einem Eingefrieren des Mediums (Wasser) erklärt werden.

Remedy:
Monitoring the temperature of the fluid and regular check-ups for corrosion attack on the outer surfaces of the pipe bends were recommended as remedial measures for avoiding damage of this nature.

Our services – your benefits:
An analysis of the damage has made the customer aware of weak spots in the operation of his cooling system that can be eliminated by suitable measures so as to ensure an un-disturbed operation of the equipment.

Consulting services from:
TÜV SÜD Industrie Service GmbH