Page 152 - CITS - Welder - Trade Theory

WELDER - CITS

Welding procedures qualification: The codes stipulate that all the details of the welding procedure should be
listed in the ‘Welding procedure specification’ (WPS).

Each of these welding procedure specifications shall be qualified by the welding of test coupons, and the
mechanical testing of the specimens cut from these coupons are required by this code. The welding date for
these coupons and the results of these tests shall be recorded in a document known as ‘procedure qualification
record (PQR)’.
A WPS may require the support of more than one PQR, while alternatively, one PQR may support a number of
WPSs. A WPS will be applicable equally for a plate, pipe and tube joints. The WPS should contain the following
nine points in detail.

1 Joints: details The groove design, the type of backing used etc. are to be specified in this. If a change in the
type of edge preparation (Single Vee, Single ‘U’ or double Vee etc.) is made or if the joint backing is removed,
a new WPS has to written but need not be qualified by a test.
2 Base metals: The base metal (P) number and the thickness ranges for which the procedure is applicable etc.
have to be mentioned here. If the range of thickness has to be increased or a change of base metal from one
‘P’ number to another ‘P’ number is required, a new WPS should be prepared and supported by a PQR after
due tests.
3 Filler metals: The details of the electrodes, and filler wires such as the ‘F’ number, ‘A’ number and the type of
the filler metals have to be specified here. The electrodes, flux compositions, (basic, rutile, etc.) are also to be
mentioned. A change in ‘F’ number or ‘A’ number shall require a new WPS and PQR. A change in the diameter
of the electrode also requires a new WPS but need not be qualified by a test. The addition or deletion of filler
metals requires a new WPS and PQR after re-tests.

4 Position: The positions in which the welding should be done shall be mentioned here. The qualification test
can be done in any position but still the same procedure is applicable to all positions.
5 Preheating: The preheating temperature, inter pass temperature etc. shall be clearly specified. If the preheat
is to be decreased by more than 550C, then a new WPS has to be prepared and qualified by a test.
6 Post: weld heat treatment The temperature and soaking time of the post-weld heat treatment shall be shown
here. Any change in this shall require a new procedure qualification.
7 Electrical characteristics: The type of current, (AC or DC) polarity, amps and voltage etc. have to indicated
here.

8 Gas: The shielding gases flow rate, details of gas purging etc. will be shown here. Change in gas composition
will call for re-qualification.
9 Technique: The details of the welding techniques string or weave bead, method of initial and inter pass
cleaning, back gouging, single or multiple passes, root grinding etc., shall be written here. The test welding can
be done either in a plate or pipe material and in any position. The maximum thickness for which the procedure
is applicable is generally twice the thickness of the test plate or pipe. The welder who welds the test joint is also
qualified for that procedure but only in that position in which he welds whereas the procedure is applicable to
all positions. The results of the tests shall be recorded in the PQR including welding, NDT and mechanical test
results.
Welder’s qualification: The purpose of the welder’s qualification is to determine the ability of the welder to make
sound welds.
The welder may be qualified, based on the results of the mechanical test (two face bends and two root bend tests
or four side bend tests) or by radiographic examination of a minimum length of 150 mm for a plate or the entire
weld for a pipe. The position of the weld joint has been classified as 1G, 2G, 3G, 4G, 5G and 6G. Table 4 shows
the positions qualifying for other positions.

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CITS : C G & M - Welder - Lesson 46 - 48 CITS : C G & M - Welder - Lesson 46 - 48