radiography of welds

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Radiography of welds
ALL CRITICAL WELDS REQUIRE ONE OR MORE METHODS
OF NDT TO ASSURE QUALITY , ENSURE SAFETY AND
PROVIDE OVERALL SYSTEM RELIABILITY.
RADIOGRAPHY IS ONE OF THE ESSENTIAL METHODS TO
CERTIFIY THE WELD FOR ITS SOUNDNESS, BECAUSE IT
PROVIDES
1. A PERMANENT RECORD
2. A BEST METHOD TO RECORD ALL VOLUME
DISCONTINUITIES,
3. THE RADIATION SOURCES ARE SUITABLE TO
OPERATE AT BOTH FIELD AND SHOP FLOORS
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TECHNIQUES; SWSI

SINGLE WALL SINGLE IMAGE TECHNIQUE,SWSI.

RADIATION PENETRATES ONE WALL AND ONE WALL
IMAGE IS OBTAINED FOR INTERPRETATION.

SHALL BE PRACTICED WHENEVER PRACTICABLE.

ALL THE DESIRED QUALITY OF A RADIOGRAPH SUCH AS
HIGHEST CONTRAST, ADEQUATE DENSITY, LEAST
DISTORTION, SHARPEST DEFINITION ARE EASILY
ACHIEVED BY THIS TECHNIQUE.
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DWSI-DOUBLE WALL SINGLE IMAGE

WHEN EITHER SOURCE OR THE FILM CAN NOT BE

PLACED INSIDE THE PIPE (NORMALLY LONG PIPE
LINES) DWDI IS THE ONLY CHOICE TO PRACTICE.

RADIATION PENETRATES TWO WALLS AND IMAGE IS
OBTAINED FOR ONE WALL –THE WALL CLOSEST TO
FILM AND FARTHEST FROM THE SOURCE.

THE ENTIRE CIRCUMFRENCE IS DIVIDED SUITABLY
TO ACCOMADATE EXPOSURE REQUIREMENTS AND
FILM SIZE SEE THE NOTES

LOCATION MARKERS, IQI, ARE ALL PLACED ON THE
FILM SIDE AS THERE IS NO OTHR CHOICE.
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DOUBLE WALL DOUBLE IMAGE –
DWDI.

PIPES WELD HAVING LESS THAN 3.5 INCH DIA., NEITHER SWSI,
NOR DWSI CAN BE PRACTICED.

DWDI IS THE ONLY CHOICE.

RADIATION PENETRATES TWO WALLS AND TWO IMAGES ARE
OBTAINED FOR INTERPRETATION BY OFF SETTING THE
SOURCE TO GET AN ELLIPTICAL SHOT. IN ORDER TO
PRODUCE A RADIOGRAPH WITH MINIMUM Ug LARGE SFD
SHALL BE GIVEN TAKING OD AS THE DISTANCE BETWEEN
THE OBJECT AND FILM.

AT THE EXTREEME CONE OF RADIATION THE WALL THICKNESS

CONSIDERABLY INCREASES FOR PENETRATING RADIATION
AND THIS AREA DO NOT PRODUCE SUITABLE IMAGE WITH
REQUIRED DENSITY.

HENCE TWO EXPOSURES ARE ESSENTIAL AT 90° APART.
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DOUBLE WALL DOUBLE IMAGE –
DWDI.

PIPES WELD HAVING LESS THAN 3.5 INCH DIA., NEITHER SWSI,
NOR DWSI CAN BE PRACTICED.

DWDI IS THE ONLY CHOICE.

RADIATION PENETRATES TWO WALLS AND TWO IMAGES ARE
OBTAINED FOR INTERPRETATION. IN ORDER TO PRODUCE A
RADIOGRAPH WITH MINIMUM Ug LARGE SFD SHALL BE GIVEN
TAKING OD AS THE DISTANCE BETWEEN THE OBJECT AND
FILM.

AT THE EXTREEME CONE OF RADIATION THE WALL THICKNESS
CONSIDERABLY INCREASES FOR PENETRATING RADIATION
AND THIS AREA DO NOT PRODUCE SUITABLE IMAGE WITH
REQUIRED DENSITY.

HENCE TWO EXPOSURES ARE ESSENTIAL AT 90 DEGREE ARE
ESSENTIAL.
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DOUBLE WALL SUPERIMPOSED
TECHNIQUE:


THICK WALL TUBES HAVING OD/ID RATIO >1.414 DWDI
TECHNIQUE WILL NOT COVER COMPLETE AREA FOR
INSPECTION.

SO DOUBLE WALL SUPER IMPOSED TECHNIQUE IS
PRACTICED BY PLACING THE SOURCE VERTICALLY
ABOVE THE WELD AND BOTH THE IMAGES ARE
SUPERIMPOSED ONE ABOVE THE OTHER.

MINIMUM THREE EXPOSURES AT 120 DEGREE
APART ARE REQUIRED, BUT ACTUAL NUMBER OF
SHOTS REQUIRED = 1.7(OD/ID), CORRECT TO THE
NEXT HIGHEST INTEGER.
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PRACTICAL APPLICATIONS OF
THE VARIOUS TECHNIQUES.

SWSI:

PLATE WELDS, CIRCUMFRENTIAL AND
LONGITUDINAL JOINTS IN LARGE VESSELS,
CASTINGS,

STORAGE TANKS, HORTONSPHERES,

ASSEMBLIES
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SWSI PARAMETERS
WELD TYPE SFD IQI ENERGY

CONE
ANGLE
PLATE-BUTT T{f/ug+1} SS For single
wall
Half cone
angle 23°
CS –LARGE
DIA
SAME
AS
ABOVE
SS FOR
SINGLE
WALL
PANAROMA
IC Source at
the centre
CS- SAME
AS
ABOVE
SS SAME AS
ABOVE
SOURCE
INSIDE FILM
OUTSIDE-
PREFERED
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DWSI EXPOSURE PARAMETERS

* OUT SIDE BETWEEN A & B


FILM OUT SIDE

IQI F SIDE

ENERGY=

2 WALL THK

DE IS THE

PRESENT SEGMENT DE
A
C
D
E
F
B
*
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DWDI PIPE OD < 3.5 “

* OFF SET

SFD=OD{f/Ug+1}

IQI SS SIDE

FILM OUTSIDE, DOUBLE WALL VIEWING


ELLIPTICAL EXPOSURE –2 EXP. IF OD/ID < 1.414
*
*
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DW SUPER IMPOSED
PIPES OD < 3.5 “ BUT FOR HEAVY WALL THICKNESS
THAT IS OD/ID RATIO > 1.414
MINIMUM 3 EXP. ACTUAL NUMBER OF EXP= 1.7(OD/ID)
IMAGES OF SS AND FS ARE SUPERIMPOSED.
*
1
2
3
4
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HINTS FOR PRACTICE
AS THE RADIATION CONE IS DIVERGING THE FILM SHALL
BE PREFERABLY PLACED ON CONVEX SIDE –AVOID ON
CONCAVE SIDE AS FAR AS PRACTICABLE.
THE SELECTION OF SOURCE DEPENDS UPON THE HVT
THICKNESS OF THE JOB UNDER INVESTIGATION, TO GET
THE REQUIRED CONTRAST ON THE FILM THE JOB
THICKNESS SHALL BE AT LEAST 2HVTS OR MORE w.r.t TO
THE SOURCE.
CORRECT EXPOSURE GIVES A SATISFACTORY
RADIOGRAPH, IMPROPER EXP. SHALL NOT BE
COMPENSATED WITH TIME OF DEVELOPMENT.
HIGHEST CONTRAST, ADEQUATE DENSITY, SHARPEST
DEFN, & LEAST DISTORTION ARE THE BASIC
REQUIREMENT FOR A RADIOGRAPH.

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RADIOGRAPHIC IMAGE
QUALITY- SENSITIVITY
2-2T LEVEL OF INSPECTION:
THE FIRST 2 FOR CONTRAST AND 2T FOR DEFN.
IMAGE QUALITY DEPENDS BOTH ON CONTRAST AND
DFN.
SENSITIVITY
I Q I
CONTRAST
DEFN
2
2T
2
SUBJECT FILM
Ug
Uf Ui
Um
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REASONS FOR POOR QUALTIY
RADIOGRAPHS.
1. ARTIFACTS
2. WRONG SELECTION OF SOURCE/ENERGY
3. WRONG SELECTION OF TECHNIQUE
4. SHORT SFD AND LONG OFD
5. WRONG SELECTION OF FILM, SCREEN AND FILM
SCREEN COMBINATION
6. PREVENTION OF BACK SCATTER, SIDE SCTTER
AND FORWARD SCATTER
7. IMPROPER PROCESSING

8. POOR ILLUMINATOR & ILLUMINATION
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