radiography of welds

radiography of welds

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

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

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

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.

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.

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

PRACTICAL APPLICATIONS OF

THE VARIOUS TECHNIQUES.

 SWSI:

 PLATE WELDS, CIRCUMFRENTIAL AND

LONGITUDINAL JOINTS IN LARGE VESSELS,

CASTINGS,

 STORAGE TANKS, HORTONSPHERES,

 ASSEMBLIES

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-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

*

DWDI PIPE OD < 3.5 “

 * OFF SET

 SFD=OD{f/Ug+1}

 IQI SS SIDE

 FILM OUTSIDE, DOUBLE WALL VIEWING

*

*

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

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

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

2

2T 2

SUBJECT FILM Ug Uf Ui Um

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

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