Page 115 - Ship Construction.DJ Eyres 6Ed

Ch10-H8070.fm Page 104 Wednesday, October 18, 2006 7:37 AM
104 Ship Construction
The inserted plate panel is then welded to within 300 to 375 mm of the free
edges, the butts are completed, and then the seams after welding any longi-
tudinal stiffening across the butts. Finally the vertical framing is welded in
way of the seams (Figure 10.4).

Testing Welds
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For economic reasons much of the weld testing carried out in shipbuilding
is done visually by trained inspectors. Spot checks at convenient intervals
Dye penetrantห้องสมุด ศูนย์ฝกพาณิชย์นาวี
are made on the more important welds in merchant ship construction
generally using radiographic or ultrasonic equipment. Welding materials
are subjected to comprehensive tests before they are approved by Lloyds
Register or the other classification societies for use in ship work. Opera-
tives are required to undergo periodical welder approval tests to ascertain
their standard of workmanship.

WELD FAULTS Various faults may be observed in butt and fillet welds.
These may be due to a number of factors, bad design, incorrect welding
procedure, use of wrong materials, and bad workmanship. Different faults
ึ
are illustrated in Figure 10.5. The judgment of the seriousness of the fault
rests with the weld inspector and surveyor, and where the weld is considered
to be unacceptable it will be cut out and rewelded.

Non-destructive Testing

For obvious reasons some form of non-destructive test is required to enable
the soundness of ship welds to be assessed. The various available non-
destructive testing methods may be summarized as follows:

งาน
Visual examination
Magnetic particle
Radiographic
Ultrasonic

Of these five methods, the dye penetrant and magnetic particle tests have
a small application in ship hull construction, being used for examining for sur-
face cracks in stern frames and other castings. Visual, radiographic, and ultra-
sonic examinations are considered in more detail, as they are in common use.
Magnetic particle testing is carried out by magnetizing the casting, and
spreading a fluid of magnetic particles (e.g. iron fillings suspended in paraf-
fin) on the surface. Any discontinuity such as a surface crack will show up as