radiography of welds
03/12/14 1 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 03/12/14 2 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. 03/12/14 3 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. 03/12/14 4 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. 03/12/14 5 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. 03/12/14 6 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. 03/12/14 7 PRACTICAL APPLICATIONS OF THE VARIOUS TECHNIQUES. SWSI: PLATE WELDS, CIRCUMFRENTIAL AND LONGITUDINAL JOINTS IN LARGE VESSELS, CASTINGS, STORAGE TANKS, HORTONSPHERES, ASSEMBLIES 03/12/14 8 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 03/12/14 9 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 * 03/12/14 10 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 * * [...]... SUBJECT 03/12/14 I Q I FILM DEFN 2T Ug Uf Ui Um 13 REASONS FOR POOR QUALTIY RADIOGRAPHS 1 2 3 4 5 6 7 8 ARTIFACTS WRONG SELECTION OF SOURCE/ENERGY WRONG SELECTION OF TECHNIQUE SHORT SFD AND LONG OFD WRONG SELECTION OF FILM, SCREEN AND FILM SCREEN COMBINATION PREVENTION OF BACK SCATTER, SIDE SCTTER AND FORWARD SCATTER IMPROPER PROCESSING POOR ILLUMINATOR & ILLUMINATION 03/12/14 14 … 03/12/14 15... 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 3 03/12/14 2 4 11 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... 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 03/12/14 12 REQUIREMENT FOR A RADIOGRAPH 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