API 570 EXAM STUDY GUIDE [MODULE 6 : PART 3] ASME SECTION V RADIOGRAPHIC EXAMINATION

ASME BPVC SECTION V
ARTICLE 2 RADIOGRPAHIC EXAMINATION

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T-261 : Source Size

Source Size verification

The equipment manufacturer’s or supplier’s publications, such as technical manuals, decay curves, or written statements documenting the actual or maximum source size or focal spot, shall be acceptable as source size verification.

Source Size refers to radioactive material sources and Focal spot refers to X-Ray machines.

 The code says that the source size /focal spot size can be taken from the above documents.

If it is not available in any of those documents, it is to be determined by the methods as defined in this document. 

For X-Ray Machine of  1000kV and less,  Focal Spot Size is determined by Pinhole Imaging in accordance with SE-1165.

For Iridium-192 Sources, Source size is determined in accordance with SE-1114

It is interesting to note that for X-Ray machine of >1000KV and sources other than Iridium the code is not specifying the method of determining the source size.

Remember: pinhole imaging is related to X-Ray source size determination.

  T-262 Densitometer and Step Wedge Film

The contents under this clause is a little bit confusing. Please read the clause completely from T-262.1 to T-262.4 . 

There are four terms

1. National Standard step tablet
2. Step wedge calibration film
3. Densitometer
4. Step wedge comparison film

We will start with National Standard step tablet.

1. National Standard step tablet: 

The master calibrator having at least five steps with neutral densities from atleast 1.0 through 4.0

We can have another national step tablet which is calibrated from the master calibrator (That is a national standard step tablet). This national step tablet calibrator is used to calibrate densitometer.

2. Step Wedge Calibration Film

Condition 1: A newly purchased step wedge calibration film without opening the original packing or purchased earlier but in the original packing.

Prior to first use, if the step wedge calibration film is maintained in the original light-tight and waterproof sealed package as supplied by the manufacturer, it can used directly.

 Condition 2: The original packing is already opened.

Step wedge calibration films may be used without verification for one year upon opening provided it is within the manufacturers stated shelf life.

Condition 3: The above two conditions are not met.

The step wedge calibration film shall have been verified within the last year by comparison with a national standard step tablet.

3. Densitometer:

Densitometer is calibrated atleast every 90 days using either with a National Standard Step Tablet or with a Step Wedge Calibration Film.

Procedure for calibration.

1. The densitometer manufacture's step-by-step instructions shall be followed for the calibration of densitometer.

2. The density steps closest to 1.0, 2.0, 3.0 and 4.0 on the national standard step tablet or step wedge calibration film shall be read.

3. The densitometer shall show densities with in 士0.05 density units from the actual density stated on the national standard step tablet or step wedge calibration film.
3. Step Wedge Comparison Film:
Step wedge comparison film is used for day-to-day density checking purpose.

1. Shall be verified prior to first use
2. Shall be verified by a calibrated densitometer
3. The step wedge comparison film is acceptable if the density readings do not vary by more than 士0.1 density units from the density stated on the step wedge comparison film

Periodic Verification
This refers to the verification's that are to be done on densitometer and step wedge comparison film on day-to-day basis.
Periodic Verification of Densitometer
Periodic calibration verification checks shall be performed on any of the conditions which comes first.

1. The begining of each shift
2. After 8hrs of continuous use
3. After change of apertures

Documentation of calibration and periodic verification records

The calibration of densitometer and step wedge calibration/comparison shall be documented as below , but the actual readings for each step do not have to be recorded.

1. Densitometer calibrations shall be documented
2. Periodic densitometer verification checks do not have to be documented
3. Step wedge calibration film verification shall be documented
4. Step wedge comparison film verification shall be documented.

T-270: EXAMINATION

RADIOGRAPHIC TECHNIQUE

Whenever practical - Single Wall exposure technique; if not practical double-wall technique to be used.

No of exposures required:  Exposures should provide proper coverage.

Single-wall technique: 

The radiation passes through one wall of weld/material

Double-Wall technique:

1. Single-Wall viewing

Weld/Material on the film side is viewed for acceptance.  When complete coverage is required for circumferential welds (materials), a minimum of three exposures taken 120 deg to each other shall be made.

 2. Double-Wall viewing

Materials and for welds in components 3 1/2 in. (89 mm) or less in nominal outside diameter can be radiographed by this technique.

a. Ellipse

For welds, the radiation beam may be offset from the plane of the weld at an angle sufficient to separate the images of the source-side and film-side portions of the weld so that there is no overlap of the areas to be interpreted. When complete coverage is required, a minimum of two exposures taken 90 deg to each other shall be made for each joint.

b. Superimpose

As an alternative, the weld may be radiographed with the radiation beam positioned so that the images of both walls are superimposed. When complete coverage is required, a minimum of three exposures taken at either 60 deg or 120 deg to each other shall be made for each joint.

T-272 Radiation Energy

Radiation energy is selected so that it shall achieve the density and IQI image requirements of Article 2 of ASME BPVC Sec V.

Note: The density and IQI requirements of Article 2 should be met in a radiograph and NOT of construction code.

T-273 Direction of Radiation

The direction of the central beam of radiation should be centered on the area of interest whenever practical.

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