Quiz – Section 11 Procedures for Nondestructive Testing (NDT)- CWI Part C- 10 Questions
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Section 11 Procedures for Nondestructive Testing (NDT)
Written procedures are required for all NDT procedures.
1 1 .1 Radiographic Test Methods
Paragraph 11 .1 .1 addresses requirements for radiographic examination of welds using flam or other media. It describes the flam characteristics (appropriate density, clarity, and contrast) necessary to produce the requisite images. Images produced by other systems shall have the necessary sensitivity to clearly define the essential wire diameter of the proper image quality indicator (IQI ), sometimes referred to as a “penetrometer.”
All image quality requirements apply equally to images produced by x-rays or gamma rays. Paragraph1 1.1.2 reiterates the fact that written procedures are required and refers the reader to paragraphs 11 .1 .2.2 for the details to be addressed in procedures for flam radiography and to paragraph 11 .1 .2.3 for the details to be addressed in procedures for techniques that use other imaging media.
Paragraph 1 1 .1 .3 addresses exposure geometry, which is the relationship between the radiation source, the part being inspected, and the flam or other medium. Three exposure geometries are defined. Single wall exposure/single wall viewing (SWE/SWV) is an exposure where the radiographic source is centered inside the pipe with the flam on the outside of the pipe so that, at all locations on the flam, the radiation goes through a single wall thickness before it reaches and exposes the flam and the flam only shows one wall thickness. When the radiographic source is outside the pipe, but no more than ½ inch from the weld surface and the flam is on the opposite side of the pipe, three exposures separated by 120 degrees are required to examine all 360 degrees of the weld. This is referred to as double wall exposure/ single wall viewing or DWE/SWV, in which radiation passes through two pipe wall thicknesses before it reaches and exposes the flam, but only the flam -side portion of the wall thickness is visible on the flam and can be read for evaluation of the weld. This is also sometimes referred to as a “contact shot.” When the radiographic source is outside the pipe and more than 1 /2 inch from the weld surface, at least four exposures 90 degrees apart are required to examine all 360 degrees of the weld. This is also referred to as DWE/SWV. However, for pipe having diameters of 3-1 /2 inches or less, a double wall exposure/ double wall viewing (DWE/DWV) technique may be used, in which the source is offset from the plane of the weld so that the weld appears as an ellipse on the flam. In this case, two exposures separated by 90 degrees are required, as a minimum, for the evaluation of the full 360 degrees of the weld.
Paragraph 1 1 .1 .4 introduces image quality indicators (IQIs) and gives basic information about their characteristics and use. IQ is shall be either the ASTM E747 wire type or the ISO 1 9232-1 wire type. The wires shall be “radiographically similar” to the pipe and weld material being examined, meaning that they must have the same or very nearly identical density to that of the materials being examined. The company will decide which IQI type is to be used.
The “essential” wire diameter is the smallest wire that must be seen clearly across the area of interest on the flam. Since the wires are placed across the weld, the area of interest is, obviously, the weld. The essential wire diameter is specified, based on weld thickness, in Table 8 on page 58 for ASTM E747 wire-type IQIs and in Table 9 on page 59 for ISO 1, 9232-1 wire-type IQ Is. Note that the essential wire diameter is based on weld thickness, not just nominal wall thickness, so this means that the thickness to be used in these tables is the nominal wall thickness plus weld reinforcement on both the outside and inside of the pipe weld. At the company’s option, smaller wire diameter IQIs may be used, as long as the minimum required sensitivity is obtained.
The details of IQIs to be used are addressed in paragraph 1 1 .1 .5. The ASTM E747 wire-type IQI has six wires while the ISO 1 9232-1 wire-type IQI has seven wires, both of which arrange the wires in order of increasing diameter. These tools are used to ensure the radiographic technique’s minimum sensitivity, which is usually the ability to resolve any indication whose maximum dimension is 2 % of the weld thickness or greater.
The placement of IQIs is described in paragraph 1 1 .1 .6. Wire-type IQIs are typically placed on top of the weld with the wires transverse to the weld. The location (source side vs. film side) is a function of the exposure geometry. When a weld is radiographed in a single exposure with the radiation source inside of the pipe (SWE/SWV), a minimum of four IQIs, equally spaced around the outside of the pipe, is required. For DWE/DWV procedures, a single IQI on the source side of the pipe is required. For DWE/ SWV and SWE/SWV procedures requiring multiple exposures or films to cover all 360 degrees of the weld and where the length of the film to be interpreted exceeds five inches, two IQIs located on the film side are required.
When placing IQIs across the weld is impractical due to weld reinforcement or profile, the IQI may be placed on a separate block of similar material, also called a “shim,” is used to elevate the IQI to a height level with the top of the weld reinforcement.
Paragraph 1 1 .1 .7 limits the interpretation of radiographic images of production welds to Level II or Level III radiographers. Radiographers are required to report all defects to the company unless the company specifically requires all imperfections to be reported. The radiographers shall state whether the welds meet the requirements of Section 9 of API 1104, but the company shall determine the final disposition of the welds.
Paragraph 1 1 .1 .8 requires that lead letters, numbers, or markers be placed on the weldment to identify the radiographic image relative to the weld. This will allow the defects identified on the film to be located on the weld so that repairs can be accurately located.
Improper storage of unexposed film can render it unsuitable for use. Paragraph 1 1 .1 .9 recognizes this hazard and requires an unexposed film to be stored in a clean, dry place and it also explains the characteristics of the damaged film.
All flam must exhibit the same level of quantitative blackening, referred to as “transmitted density,” when exposed to the same intensity of radiation. This transmitted density can be limited by pre-ex postures fog on the unexposed flam. There is a limit to the amount of pre-exposure fog permitted on unexposed flam. For transparent-based flam, the pre-exposure fog cannot exceed 0.30 H & D transmitted density; for opaque-based flam, this pre-exposure fog can be no more than 0.50 H & D reflected density, where “H & D” is the Hurter-Dry Feld method of defining the quantitative blackening of flam.
Paragraph 1 1 .1 .1 0 gives the flam quality requirements for the areas of interest for developed flam. Except for small areas on the flam corresponding to irregular weld configurations, the transmitted H & D density of transparent-based flam shall be between 1 .8 and 4.0, inclusive; the reflected H & D density of opaque-based flam shall be between 0.5 and 1 .5, inclusive. Paragraph 1 1 .1 .1 0.4 states that, when requested by the company, the flam or other imaging media must be processed, handled, and stored so that the images are interpretable for at least three years after they are produced.
1 1 .2 Magnetic Particle Test Method
A procedure for magnetic particle testing (MT) must be written, qualified by demonstration, and accepted by the company prior to use. The MT procedure must comply with ASTM E709, Standard Guide for Magnetic Particle Testing.
1 .3 Liquid Penetrant Test Method
A procedure for liquid penetrant testing (PT) must be written, qualified by demonstration, and accepted by the company prior to use. The PT procedure must comply with ASTM E1 65, Standard Test Method for Liquid Penetrant Examination.
1 1 .4 Ultrasonic Test Methods
A detailed procedure must be developed, qualified by demonstration, and agreed upon by the contractor and company. The use of ultrasonic testing (UT) shall be at the option of the company. The pipe being inspected with UT must be uncoated and the inspector should be aware of surface conditions that can interfere with scanning. Pipe seams should be ground fuse.
Paragraph 1 1 .4.2 describes the elements required to be addressed in the written procedures for ultrasonic testing of welds. This includes calibration requirements.
Paragraph 1 1 .4.3 states that only NDT Level III UT personnel are permitted to develop application techniques and prepare and approve the procedures. However, both Level II and Level III UT personnel are permitted to calibrate equipment and interpret the test results. Similarly, both Level II and III UT personnel are permitted to perform the tests and evaluate the results per the acceptance criteria.
The company has the right to require personnel to demonstrate their ability to perform to the requirements of the procedure as described in paragraph 1 1 .4.4.
Paragraph 1 1 .4.4 requires that the UT procedure, as well as the system/equipment to be used, must be demonstrated and this demonstration must be accepted by the company. This demonstration must also be documented in a report which must address the following:
(a) Welds containing defects and acceptable discontinuities must be prepared from actual production material using a qualified welding procedure.
(b) Radiographs shall be made of the welds and the results documented.
(c) The UT procedure shall be applied to the welds and the results documented and compared with the radiographs.
(d) Differences in detection results shall be documented. Destructive testing will usually be necessary to confirm the results or document discrepancies. This, however, is at the option of the company.
(e) The use of the UT procedure on production welds is then based on the capability of the method/ systems to:
1 ) Circumferentially locate,
2) Size for length,
3) Determine the depth from the OD surface, and
4) Axially locate (across the weld cross-section) the discontinuities/defects in the test welds.
Paragraph 1 1 .4.5 requires the sensitivity of the UT process and equipment to meet minimum requirements. This is accomplished by applying the procedure to known reference standards and specifying the minimum magnitude (screen height) of return echoes produced by standard geometric conditions. The reference block used for this is shown in Figure 27 on page 64. The block must be made by introducing a standard N1 0 notch, as shown in the figure, into a sample of the pipe material to be inspected. The highest point of the distance-amplitude-corrected (DAC) or time-corrected gain (TCG) echo produced by this notch shall not be less than 80 % of the full-screen height on the UT display. Adjusting the equipment to meet this requirement will ensure proper calibration. Requirements for the
sensitivity of the automated UT procedure follows a similar approach, except that fat-bottomed holes must be machined into a sample of the pipe to be inspected, in addition to the N1 0 notches.
Paragraph 1 1 .4.6 requires that parent material be screened for flaws that may interfere with the weld inspection. Before ultrasonic testing of a completed pipe weld is begun, a compression wave test must be conducted on both sides of the weld to locate any refactors in the parent material that may interfere with the weld inspection. Once the parent material is determined to be sound or any refactors in the parent metal are located and documented, the weld may be inspected.
Paragraph 1 1 .4.7 identifies the reference scanning sensitivity and screen height requirements for manual compression wave and the automatic testing of the parent material and the scanning and evaluation sensitivities for the manual and automated testing of welds. Determination of the reference sensitivity for the parent material and inspection of the weld must be performed and documented independently.
Paragraph 1 1 .4.8 requires UT technicians to report only defects unless the company specifically requires that all indications (evaluation level and above) be reported.
Paragraph 1 1 .4.9 specifies that the UT report shall list the weld number, datum location, length, depth from the OD surface, and the defect classification (linear, transverse, or volumetric) for each reported indication.