Volume-II of IV - GAIL

MECON LIMITED
REGD. OFF : RANCHI (BIHAR)
PROCESS & PIPING
DESIGN SECTION
NEW DELHI
STANDARD SPECIFICATION
TITLE WELDING OF ONSHORE GAS
SPECIFICATION NO. PAGE 27 OF 48
PIPELINES
MEC/S/05/62/02 REVISION
15.6 Probes
the regulation control shall be accurate to within ±1 db and this accuracy
shall be certified by the instrument manufacturer.
may be powered by a battery or an electric generator. In the first case, the
autonomy of operation (endurance) of the instrument shall be sufficient to
carry on working without frequent interruptions, and the instruments shall
be equipped with an automatic switch which switches it off when the
battery runs down; in the second case, there must be a voltage stabilising
device with a tolerance of ±2 Volts.
The probes used shall have dimensions, frequencies, and a refraction angle
suited to the type of steel, the diameter, the thickness of the pipe and to the joint
design.
15.7 Reference Sample Pieces
The efficiency of the equipment used, the effective refraction angle of the probe,
and the beam output point, shall be checked using a V1 and V2 sample block, IIW
type or calibration block ASTM E-428.
For the calibration of runs and the regulation of detection sensitivity during the
test, a calibration piece shall be used. This piece shall be taken from the
production material, and will be at least 150mm long (measured in the direction of
the axis), and at least 50mm wide (measured in the direction of the
circumference) (see Fig. 5 of this specification).
In the middle of the inside and the outside surface of the calibration piece a
groove shall be made. The groove will have a rectangular cross-section, a flat
bottom and the following dimensions.
depth : 1 ± 0.1mm
breadth (measured parallel to the 150mm side) : 1 ± 01mm
Length (measured parallel to the 50mm side) not less than 30mm
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