Page 143 - Failure Analysis Case Studies II

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k

Fig. 14. Starboard bilge keel

8 Brittle fracture
9 Brittle fracture [l in. (25mm) in centre ductile]
10 Brittle fracture [into drainhole 1 in. (25 mm) ductile, then brittle]
11 Brittle fracture
12 Brittle fracture
13 Ductile
Generally, even where full 45" shear fracture was evident, the reduction of area accompanying
the fracture was small. An inspection of the port bilge keel remaining on the aft section of the ship
revealed cracks in two weld details similar to the bilge keel initiation site on the port side. Extraction
of these samples was requested. The heating coils used to keep the oil in the tanks at 140 OF (60 "C),
are evident in many of the figures. It must be pointed out, however, that the initiation site in the
port bilge keel would have been surrounded by sea-water, and, as such, could be considered to be
at the water temperature of -0.7 "C.
Two meetings were held between the interested parties on 16 and 17 April 1979, respectively. At
the first it was agreed by all concerned that TWI should carry out any tests required to ascertain
the reasons behind the failure. At the second meeting, the five test samples required for this
investigation selected by the DOT and TWI representatives during their inspections were described
to the interested parties, who agreed to the extraction of these samples and their shipment to the
TWI. Details of the samples required were left with the ship owners, and a Lloyds' representative
was appointed to supervise the extraction of the samples. The positions of the required test samples
were then marked on the vessel by the DOT and TWI representatives.

3. DISCUSSION OF THE RESULTS OF THE FAILURE INVESTIGATION
3.1. Introduction
Three of the samples identified during the dry dock inspection of the vessel described above
contained initiation sites. At the start of the mechanical and metallurgical test programme described
in [l], each of these samples were treated with equal importance. However, as the test programme
developed, various aspects became clearer, and the port bilge keel sample was identified as the
primary sample. To keep this section of the paper reasonably concise, rather than outline the gradual
progression of the failure investigation, the sequence of events leading to the failure of the MV