RADIOGRAPHIC TESTING OPERATING PROCEDURE
RADIOGRAPHIC TESTING OPERATING PROCEDURE
Table of Contents
- Scope 3
- Objectives 3
3 References 3
- Personnel 3
- Surface Condition 3
- Radiographic Parameters 4
- Identification of Radiographs 7
- Radiographic Techniques (Weldments) 8
9 Processing Radiographs 12
- Viewing of Radiographs 13
- Interpretation of Radiographs 13
- Acceptance Criteria 14
- Reporting 14
- Appendix 15
1. SCOPE:
This General Procedure describes the technique and parameters for radiographic testing.
This Procedure covers the material thickness range upto 200 mm in all carbon steel material or equivalent thickness in other materials.
- OBJECTIVES:
- To ensure that radiographic testing techniques employed are conducted in accordance with governing code.
- To ensure that all NDE personnel adhere to a basic standard of workmanship and report presentation.
- REFERENCES:
- ASME Sec. V: Non-Destructive Examination (1998 edition with addenda)
- BS 2600 Part 1 & 2 (1983)
- AWS D1.1: Structural Welding Code (2000 edition)
- ASNT SNT-TC-1A (1992 edition)
- In case of conflicting requirements among the referenced codes and this procedure, the requirements of ASME Sec. V – 1998 shall govern.
- PERSONNEL:
- All NDE Personnel carrying out Radiographic testing shall be qualified and certified to SNT-TC-1A (1984 & 1992 edition) and EIL Written Practice as a minimum ASNT Level I or equivalent.
- All NDE Personnel carrying out Radiographic Interpretation shall be qualified to ASNT Level II or equivalent.
- SURFACE CONDITION:
The surface of the work-piece shall be reasonably smooth and shall be free from any visible irregularities, which could mask or be confused with defects during interpretation of radiographs.
6. RADIOGRAPHIC PARAMETERS:
- Radiography shall be carried out by means of X-Rays or Gamma Ray.
The maximum source size for Iridium 192 isotope shall be 3.5 mm x 3.5 mm.
The maximum source size for Co-60 isotope shall be 3.18 x 3.1 x 3.76 mm.
The maximum focal spot size for X-Ray machines shall not exceed 5 mm square.
- SELECTION OF RADIATION SOURCES:
Any of the above radiation energy sources shall be used as long as the required radiographic sensitivity is achieved.
The recommended minimum thickness (Steel equivalent) for use of radioactive isotopes may be as follows:
Ir. 192 19.0 mm (maximum 75.0 mm)
Co-60 38.0 mm (maximum 200.0 mm)
In general and where practical X-Ray sources may be used for thickness lower than mentioned above.
The minimum recommended thickness might be reduced when radiographic techniques used demonstrate that the required sensitivity is achieved by proper selection of
- Film
- Film Density
- Geometric Unsharpness
- Selection of intensifying screens etc.,
- RADIOGRAPHIC FILM:
The film selected shall be capable of demonstrating the required penetrameter IQI sensitivity.
- Film selection shall be based on the geometric exposure parameters and shall be selected such that the requirements of radiograph sensitivity and contrast are achieved. Typical films used include the following:
ASTM Class 1: Agfa Gaevert D4 or equivalent (Ultra fine grain very high contrast).
ASTM Class 2: Agfa Gaevert D7 or equivalent (Fine grain high contrast).
- INTENSIFYING SCREENS:
Clean, smooth lead intensifying screens of minimum thickness 0.125 mm (0.005 inch) shall be used in both the front and back of the radiographic film.
- IMAGE QUALITY INDICATORS (IQI):
- Wire type IQI or strip type IQI in accordance with the Referencing Code or Specification shall be used.
- The IQI shall be placed as follows:
- With the wires across the weld in the area of most interest for wire type IQI.
- The IQI shall be placed as follows:
With the holes parallel to the length of the weld for strip type IQI.
- With the thinnest wire towards the outside of the film.
With the smallest hole towards the outside of the film.
- One IQI per film at one end of the film.
- At least three IQI’s approx 120 degree apart and evenly spaced around circumference shall be used for panoramic exposures, where the source is placed on the axis of a cylindrical object and one or more film holders are used in a single exposure.
- If IQI is fixed on the film side, a letter ‘F’ must be placed on the object to indicate that the IQI is at the film side.
- The thinnest wire distinguishable, which is required to be seen in the area of interest on the radiograph, shall be determined according to the sensitivity specified. If not specified, 2% equivalent penetrameter sensitivity shall be achieved. This means that the diameter of the essential wire to be seen as a radiographic image shall be at least 2% of the thickness of the job. For the purpose of calculation of penetrameter sensitivity, for radiographs made by the DWSI technique, only the single wall thickness shall be used in the calculation. For radiographs taken by the DWDI technique, the thickness of the job for purpose of calculation shall be twice the single wall thickness.
- BACK – SCATTER INDICATOR:
A lead letter ‘B” of thickness at least 1/16” (1.6 mm) and height at least 3/8” (9.8 mm) shall be placed on the film side of the film holder (outside surface of the cassette) to detect the presence of backscatter. Presence of backscatter shall be indicated by a light image of B on a darker background. In such cases, the radiograph will be required to be re-shoot after taking sufficient precautions that the causes for backscatter have been eliminated or countered. The presence of a dark image of the letter shall not be cause of rejection.
- SOURCE TO FILM DISTANCE:
Any source to film distance may be used provided that geometric unsharpness and other factors of radiographic film quality are maintained.
Geometric unsharpness shall be calculated by using the formula:
Ug = F x t / D
Where
Ug = Geometric Unsharpness
F = Source Size: the maximum projected dimension of the radiating source (or focal spot) in the plane perpendicular to the distance D from the weld or object being radiographed.
D = distance from source of radiation to weld or object being radiographed, in
t = distance from source side of weld being radiographed to the film. In most cases, where the film is kept in intimate contact with the weld, t is equal to the radiographed thickness.
Whilst calculating the geometric unsharpness, care should be exercised to
ensure that the units are matching.
In any case, the geometric unsharpness shall not exceed the following.
For job thickness less than or equal to 2” (51 mm): 0.02” (0.51 mm)
For job thickness greater than 2” upto 4” (102 mm): 0.03” (0.75 mm)
For job thickness in excess of 4” (102 mm): 0.04” (1.02 mm)
7. IDENTIFICATION OF RADIOGRAPHS:
- MINIMUM REQUIREMENT:
The minimum identification required to appear on the radiographs include the following:
Job Identification
Date of other chronological Identification
Company Identification
Gauge Marking showing area of interest (matching identification placed on the job).
- Indisputable cross-references between radiographs and item under examination.
7.1.2 The item or section under, examination shall be clearly identified. The datum point and direction of the number tape shall be clearly marked to ensure that accurate location of defected areas on the item or sections are revealed on the radiograph.
- ADDITIONAL REQUIREMENTS:
These may be implemented based on specific instruction of the Client and may include the following:
Client Name or Project No.
Weld Number and Repair status if any RR etc.,
Part or Item No.
Date.
- RADIOGRAPHIC TECHNIQUES (Weldments):
All the techniques shall be proven, by test shots to ensure that sensitivity, density, contrast requirements are met prior to any production work being carried out.
- DOUBLE WALL SINGLE IMAGE (APPENDIX 1 FIGURE 1)
This technique is employed for pipes of 88.9 mm OD and above, where direct access to the inside of the pipe is not possible.
- The lead number tape shall be placed adjacent to the weld, care must be
taken to ensure that the number tape does not lie on any area of the weld.
The number tape shall encompass the circumference of the weld.
- The datum part (zero position) and direction of the number tape shall be clearly marked on the pipe surface.
- The identification of the weld shall be placed adjacent to the weld but on the opposite side of the number tape, if sufficient access is available. Standard practice dictates that the identification of the weld and number tape should read in the same direction.
- The placement of the IQI shall be as follows.
Two IQI shall be placed approximately 50 mm from the end of the film.
(See appendix 2 figure 1), for pipes with OD’s exceeding 219 mm.
For pipes with smaller diameters less than 219 mm, one IQI shall be placed in the middle of the film (10 cm x 20 cm). The IQI shall be identified with the letter ‘F’.
- The radiation source shall be placed against the pipe in the weld cap opposite the film, ensuring that the axis of the weld is lined up to the centre of the film and weld.
- The entire weld circumference shall be radiographed as described in 8.1.5.
- SINGLE WALL SINGLE IMAGE (PANORAMIC) APPENDIX 1 FIGURE 2.
This technique is employed where direct access to the inside of the pipe is possible, however, this technique is limited due to minimum SFD requirements.
- The lead number tape shall be placed adjacent to the weld, and shall encompass the circumference of the weld.
- The datum point (Zero position) and direction of the number tape shall be clearly marked on the pipe surface.
8.2.3 The identification of the weld shall be placed adjacent to the weld, but on the opposite side of the number tape, if sufficient access is available. Standard practice dictates that the weld and number tape should read in the same direction.
- The placement of the IQI’s shall be as follows:
Two IQI’s shall be placed approximately 50 mm from the end of the film (10 cm x 40 cm).
(See appendix 2 Figure 1) The IQI’s shall be placed on the source side access permitting.
- The radiation source is centered in the centre of the sample plane as the weld (See Figure 2 Appendix 1).
- The entire weld circumference shall be radiographed as described in 8.2.5 where the films overlap. The overlap and length of area visible shall not be less than 10 cm.
- SINGLE WALL SINGLE IMAGE (FIGURE 3 APPENDIX 1)
This technique is employed where direct access to the inside of the pipe is possible and where the minimum SFD permits.
- The lead number tape shall be placed adjacent to the weld, and shall encompass the circumference of the weld.
- The datum point (Zero position) and direction of the number tape shall be clearly marked on the pipe surface.
- The identification of the weld shall be placed adjacent to the weld, but on the opposite side of the number tape, if sufficient access is available. Standard practice dictates that the weld and number tape should read in the same direction.
- The placement of the IQI’s shall be as follows:
Two IQI’s shall be placed approximately 50 mm from the end of the film (10 cm x 40 cm).
(See appendix2 Figure 1) The IQI’s shall be placed on the source side access permitting.
8.3.5 The source is placed on the inside wall of the pipe in the weld plane. (See Figure 3 Appendix 1).
- Alternatively, for larger pipes or vessels the source may be positioned outside the centre of the weld, provided that the minimum SFD requirements are met and sufficient coverage is obtained.
- SINGLE WALL, SINGLE IMAGE (FIGURE 4 APPENDIX 1)
This technique is employed where direct access to the inside of the pipe is not possible.
- The lead number shall be placed adjacent to the weld, and shall encompass the circumference of the weld.
- The datum point (Zero position) and direction of the number tape shall be clearly marked on the pipe surface.
- The identification of the weld shall be placed adjacent to the weld, but on the opposite side of the number tape, if sufficient access is available. Standard datum point (Zero position) and direction of the number tape shall be practice dictates that the weld and number tape should read in the same direction.
- The placement of the IQI’s shall be as follows:
Two IQI’s shall be placed approximately 50 mm from the end of the film (10 cm x 40 cm).
(See Appendix 2 Figure 1) The IQI’s shall be placed on the source side access permitting.
- The source is placed in the weld plane above the external surface of the pipe or vessel. The film shall be placed inside the pipe against the wall directly opposite the source (See Figure 4 Appendix 1).
- The SFD shall be calculated as follows:
| Material Thickness | UG Maximum in mm | |
| Under 50 mm | 0.51 mm | |
| 50 mm to 76.2 mm | 0.76 mm | |
| Over 76.2 mm to 101.6 mm | 1.016 mm | |
| Greater than 101.6 mm | 1.1778 mm |
When it is impractical to obtain the required SFD due to geometrical restrictions than a separate technique is to be employed until results are obtained where the UG does not exceed 1.778 mm.
- DOUBLE WALL, DOUBLE IMAGE (ELLIPTICAL) WITH OFFSET
(FIGURE 5 APPENDIX 1)
This technique is employed for piping less than 88.9 mm and having wall
thickness of 7.62 mm and less.
- The identification of the weld shall be placed on the film, adjacent to the pipe, but opposite the source.
- One IQI shall be placed as a minimum for one film on the source side of the pipe.
- Two level markers, normally “A” and “B” shall be placed on the pipes adjacent to the weld but at 90° to each other.
- The source is positioned at a distance of 7 times the pipe diameter and shall be offset from the weld plane so that the radiographic image of the weld forms an ellipse with the source side weld and film side weld sufficiently spaced between each other for ease of viewing and evaluation.
- Two exposures at 90°to each other i.e. an “A” exposure and a “B” exposure shall be carried out to ensure adequate coverage for the entire weld circumference.
8.6 DOUBLE WALL, DOUBLE IMAGE (WITHOUT OFFSET)
(FIGURE 6 APPENDIX 1)
This technique is employed when pipe wall thickness exceeds the following parameters on pipes of 88.9 mm and less.
| ASA SCHEDULE DD in mm | Schedule 80 (mm) | |
| 21.3 mm | 3.73 mm | |
| 26.7 mm | 3.91 mm | |
| 33.4 mm | 4.55 mm | |
| 48.3 mm | 5.08 mm | |
| 60.3 mm | 5.54 mm | |
| 73.0 mm | 7.01 mm | |
| 88.9 mm | 7.62 mm |
- The identification of the weld shall be placed on the film, adjacent to the pipe, but opposite the source.
- One IQI shall be placed on the source side of the pipe.
- Three lead markers, normally “A”, “B” and “C” shall be placed on the pipe adjacent to the weld but at 120° to each other.
- The source is positioned at a distance of 7 times the pipe diameter in the weld plane but with no offset, so that the weld radiographic image is represented as a straight weld line on the film.
- Three exposures at 120° to each i.e. an “A” exposure, “B” exposure coverage for the entire weld circumference.
- PROCESSING OF RADIOGRAPHS
This processing of exposed radiographic films is carried out manually in a light proof room equipped with suitable safe lights. Special attention must be paid to:
- Continuous agitation for the first 30 seconds in the developer
- Regular agitation whilst developing to ensure that processing artifacts do not occur.
- Adequacy of developing may be confirmed by visual observation. In general, a minimum developing time between 5 and 8 minutes at 20° C is recommended.
- After completion of development, the radiograph is passed through a water bath, which in effect stops the action of the developer and prevents contamination of the next step in fixation.
- After stopping the developing, the radiograph is introduced into the fixing solution. The film is agitated in the fixer and then kept inside the fixer for a time period approximately twice that of the developing time. The maximum time of the radiograph in fresh fixer is limited to a maximum of 15 minutes.
- After completion of fixing, the radiograph is washed thoroughly for around 20 minutes in running water.
- After this washing, the radiograph is hung to try. Drying is achieved either in the darkroom or under controlled conditions in a drying cabinet which uses circulated warmed dry air.
- The temperature in the drying cabinet is not to exceed 40° C.
10. VIEWING OF RADIOGRAPHS
- Viewing of radiographs shall be performed in a room that has a low light level, which avoids reflections, glare of shadows on the radiographs. The viewing equipment used for the interpretation of the radiograph shall have a light source of sufficient intensity to provide light for the density of the film and the visibility of the required IQI.
- The viewing condition shall be such that no light around the film is visible. The low-density portion of the film visible light shall also not interfere with interpretation. Where such areas interfere, they shall be masked to avoid interference.
- INTERPRETATION OF RADIOGRAPHS
- The density range in the area of interest shall be between but not including 1.8 and 4.0 provided that the film illuminator is adequate to be able to read high densities. If the illuminator is unable to read high densities, the test will be done again, or the illuminator changed until the film can be viewed.
- Density is measured by using a calibrated densitometer.
- Density is measured through the penetrameter near the essential wire on the radiograph.
- The maximum allowable variation of density on the radiograph in the area of interest shall be within –10% and +15% of the measured through the penetrameter.
- ACCEPTANCE CRITERIA
Acceptance criteria shall be in accordance with the referencing code or client’s specifications. The client shall specify this.
When none of the codes or client’s specification is mentioned in the contractual documents, following codes and specification shall be used as acceptance criteria.
Structural Welds, Ship’s Hull etc., – AWS D1.1 – 2000
Chilled Water Piping, Pressure Piping, Refinery Piping etc. ASME B31.1 – 1998
Welder, Weld Procedure Qualification Test ASME Sec. IX – 1998
Any other item not mentioned above ASME Sec. VIII – 1998
- REPORTING
- Reporting shall be carried out on a standard radiographic report. The following minimum information shall be recorded.
- Identification e.g. Job No., Weld No.
- Material Type and Thickness Range
- Type of equipment used i.e. Isotope or X-Ray machine
- Maximum Source Size
- SFD / FFD
- Film Brand and Designation
- Type of technique employed
- Density, Sensitivity etc.,
APPENDIX – I
| Pipe OD | Exposure Technique | Radiograph Viewing | Source Weld Film Arrangement | IQI Penetrameter | Location Marker Placement | ||
| End View | Side View | Selection | Placement | ||||
| Any | Double Wall: T-271.2 (a) Atleast 3 Exposures 120 Deg. To Each other for complete coverage | Single Wall | T – 276 and Table T – 276 | Source Side T – 277–1(a) Film Side T – 277-1(b) | Film Side T – 275.1 (b) (1) | ||
| Pipe OD | Exposure Technique | Radiograph Viewing | Source Weld Film Arrangement | IQI Penetrameter | Location Marker Placement | ||
| End View | Side View | Selection | Placement | ||||
| Any | Single Wall: T-271.1 | Single Wall | T – 276 and Table T – 276 | Source Side T – 277–1(a) Film Side T – 277-1(b) | Either Side T – 275.3 T – 275.1 (c) | ||
| Any | Single Wall T-271.1 | Single Wall | T-276 and Table T-276 | Source Side T-277.1 (a) Film Side T-277.1 (b) | Film Side T-275.1 (b) (1) |
Appendix-I, Figure 3A
| Any | Single Wall T-271.1 | Single Wall | T-276 and Table T-276 | Source Side T-277.1 (a) Film Side T-277.1 (b) | Film Side T-275.1 (b) (1) |
| 3 ½ in. or Less | Double Wall T-271.2 (b) (1) at Least 2 Exposures at 90 Deg. To Each other for complete coverage | Double Wall (Ellipse) Read Offset Source Side And Film Side Images | T-276 and Table T-276 | Source Side T-277.1 (a) | Either Side T-275.2 |
| Pipe OD | Exposure Technique | Radiograph Viewing | Source Weld Film Arrangement | IQI Penetrameter | Location Marker Placement | |
| End View | Side View | Selection | Placement | |||
| 3 ½ in. or Less | Double Wall: T-271.2 (b) (2) Atleast 3 Exposures 60 Deg. or 120 Deg. to Each other for complete coverage | Double Wall Read Super Imposed Source Side and Film Side Images | T – 276 and Table T – 276 | Source Side T – 277–1(a) | Either Side T – 275.2 |