Page 119 - Ship Construction.DJ Eyres 6Ed

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Ch10-H8070.fm Page 108 Wednesday, October 18, 2006 7:37 AM
108 Ship Construction
fine cracks which are often missed by radiography, particularly where they
lie perpendicular to the emission source.
The principle of ultrasonic inspection depends on the fact that pulses of
ultrasonic energy are reflected from any surface which they encounter.
Ultrasonic waves travelling through a plate may be reflected from the surface
of the metal and also from the surfaces of any flaws which exist in the metal.
Virtually total reflection occurs at an air-metal interface, and therefore to
--- ใช้เพื่อการศึกษาเท่านั้น---
get the ultrasonic wave into the metal a liquid is placed between the source and
metal. The pattern of reflection is revealed on a cathode ray tube, which
may be calibrated using a standard reference block. An experienced operator
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
is able to recognize flaws from the cathode ray tube display, and to some extent
recognition of defect types is possible. Apart from weld inspection, ultra-
sonic techniques are valuable for assessing the thickness of structural members.

Classification Society Weld Tests
Classification societies specify a number of destructive tests which are
intended to be used for initial electrode and weld material approval. These
tests are carried out to ascertain whether the electrode or wire-flux combina-
ึ
tion submitted is suitable for shipbuilding purposes in the category specified
by the manufacturer.
Tests are made for conventional electrodes, deep penetration electrodes,
wire-gas and wire-flux combinations, consumables for electro-slag and electro-
gas welding, and consumables for one sided welding with temporary back-
ing. Tensile, bend and impact tests are carried out on the deposited weld
metal and welded plate specimens. Other tests are made for the composition
of the weld metal deposited and possible cracking.
All works where electrodes, wire-flux and wire-gas combinations, con-
sumables for electro-slag and electro-gas welding, and consumables for one
sided welding with temporary backing are produced, and have been initially
approved, are subject to annual inspection.