VISUAL TESTING
V. EVALUATION AND REPORTING OF TEST RESULTS
Evaluating and reporting of visual test results is dependent on the applicable codes, stan- dards, specifications, contract requirements, and customer needs. Some general criteria apply to all examinations. The first requirement to be established is to determine the scope of the inspection. The second requirement is to decide “how” to inspect an object.
The third requirement is to evaluate the results in accordance with a known standard. The fourth requirement is to accurately and legibly report the results.
Visual examination has long been an integral part of construction, fabrication, and manufacturing. As mentioned in Chapter 1, the Book of Genesisin the Bible mentions the first nondestructive test, and in particular, the first visual examination. This belief can be documented in the quote, “. . . and Godsaw that is was good.” Apparently the acceptance criterion was in the eye of the beholder, in this case, the Creator. Industrial applications can be categorized into various groups, such as energy, petrochemical, aerospace, trans- portation, and construction.
The American Welding Society’s Structural Welding Code for steel requires that welds meet certain workmanship standards. Welded structures such as buildings, tubu- lar structures, and bridges must be welded in accordance with specific requirements re- garding the material, welding processes, and joint designs. Once the application is es- tablished, welding parameters are specified in the workmanship requirements. The weld quality requirements are described in the workmanship section. The section on Inspec- tion spells out the qualifications of Certified Weld Inspectors (CWIs). The tasks of the CWI include assuring that the materials, weld procedures, welder qualification and records of inspection all meet code requirements. The inspector keeps a record of qual- ifications of all welders, welding operators, and tackers; all procedure qualifications or other tests that are made; and other information that may be required. Generally, the CWI performs weld inspections in accordance with a procedure that contains the AWS Code requirements.
The American Society for Mechanical Engineers (ASME), Boiler and Pressure Vessel Code, Section V, Nondestructive Examination, Article 9, Visual Examination lists the following elements to be included in a visual examination procedure:
1. How visual examination is to be performed 2. Type of surface conditions available
3. Method or tools for surface preparation, if any 4. Whether direct or remote viewing is used
5. Special illumination, instruments, or equipment to be used, if any 6. Sequence of performing examination, as applicable
7. Data to be tabulated, if any 8. Report forms to be completed
The procedure should also contain or reference a report of the approach used to demon- strate that the examination procedure was adequate (procedure qualification).
In general, a fine line, 1/32 in. (0.8 mm) or less in width, or some other artificial flaw located on the surface to be examined or a similar surface is considered satisfactory evi- dence that the procedure is adequate. To prove the procedure, the line or artificial flaw should be located in the most unfavorable location on the area being examined. It is com- mon to list acceptance criteria for various product forms in the procedure. The product forms should be specified in order to reduce the number of different visual procedures needed. In any case, substituting equipment with that of a different manufacturer or changing the details of the test parameters may require procedure requalification.
Reports
Depending on specific code requirements, a written report may be necessary. The report may contain the following for general applications:
1. Date of test
2. Examination procedure used
3. Illuminators and illumination requirements 4. Instruments, equipment, and tools
5. Test results
6. Inspector’s signature and certification level
When specific product forms are expected to be examined repeatedly, it may be appropri- ate to design a report with attributes specific to the examination.
A report of the results of a weld examination may include the following items:
1. Surface finish 2. Discontinuities 3. Undercut 4. Overlap 5. Concavity 6. Convexity 7. Weld dimensions 8. Alignment
9. Evidence of mishandling 10. Arc strikes
11. Other appropriate observations
A report of the results of bolting examinations may include the following items:
1. Discontinuities 2. Necking down 3. Erosion
4. Crevice corrosion
A report of the results of valve examinations may include the following items:
1. Surface markings 2. Stem conditions
3. Seating surface cracks, scratches, galling, etc.
4. Guide surface clearances, wear, galling, corrosion, misalignment 5. Internal body surface erosion, wear, steam cutting
6. Stem-to-wedge connection for wear and corrosion
7. Diaphragms (if applicable) checked for aging, damage, cracking
8. Ball joints (if applicable) should be checked at bearing surfaces and position stops for wear
9. Hinge pins (if applicable) should be checked for wear, clearances, and misalignment 10. Stuffing boxes (if applicable) should be checked for steam cutting, corrosion,
and mishandling.
A report of the results of pump exams may include the following items:
1. Erosion 2. Corrosion 3. Pitting 4. Leaching
5. Broken or lose parts 6. Debris
7. Shaft alignment
A report of the results of hanger, support, snubber, and restraint examinations may in- clude the following items:
1. Galled or scraped areas of pipe surface (wear) 2. Loose nuts, pins, bolts, and locking pins
3. Oversized and undersized gaps and clearances 4. Distortion of the restraint
5. No freedom of movement or locked-up conditions 6. Extensive or deep corrosion
7. Cracked welds or broken parts 8. Stripped threads
9. Elongated bolt holes 10. Necked-down bolts or rods 11. Sheared rods
12. Debris 13. Loose parts 14. Erosion
Note: Snubbers have special performance requirements unique for each application.
These functional requirements exceed the normal visual examiner’s scope of inspec- tion.
A report of the results of vessel exams may include the following items:
1. Loose parts 2. Debris
3. Abnormal corrosion products 4. Wear
5. Erosion 6. Corrosion
7. Loss of integrity (broken or cracked)
Reports of visual examination results may be supplemented by special recording me- dia or other permanent electronic record forms. Whenever questionable conditions or in- dications are encountered, some form of a permanent record should be considered. Stan- dard or digital cameras with sufficient resolution to discern and record the attribute or condition of interest are excellent means of accomplishing this. Digital cameras usually include special computer programs that allow the image to be imported directly into the electronic report. Videotape recordings are useful for large areas that are being examined.
This approach is especially helpful in providing evidence of coverage and the examina- tion technique applied. Video camera recordings may also permit a picture frame to be
“captured” and recorded directly on the electronic media report. Historically, sketches are simple and can be very helpful in recording examinations and providing location data re- garding various discontinuities. Sketches have the disadvantage of incorporating the in- spector’s perception and subsequent misinformation that would not be in a photograph.
Sketches made manually also may not be legible. Photographs and electronic images should include, where possible, a scale in order to permit the comparison of size and dis- tance. Any disorientation of angle between the scale and the line of sight (sometimes re- ferred to as “parallax”), could distort the true dimensions of an attribute, discontinuity, or condition. The use of a scale will usually provide a better perspective and result in better accuracy.
Acceptance Criteria
Acceptance criteria for welds will be as designated by the applicable code or specification and will usually include the following discontinuities:
1. Cracks
2. Incomplete penetration 3. Crater pits and cracks 4. Arc strikes
5. Undercut (dimension will be specified)
6. Surface porosity (usually defined by a maximum single size or some formula of ag- gregate amount in a total length of weld)
7. Slag (surface) 8. Spatter
9. Burn-through or melt-through 10. Overlap and rollover
11. Lack of fill
12. Excessive reinforcement
Specific acceptance criteria can be found in various codes, specifications, and standards.
In many cases, they will be specified as part of the contract requirements.
Records of inspections or examinations should also include statements indicating part acceptance (if applicable), and include appropriate documentation to support findings. In- spection report forms should be complete, legible, concise, and signed and dated. If cor- rections are necessary, they should be made with a single line through the entry error, ini- tialed, and dated. All reports, results, and/or drawings, sketches, photos, electronic files, digital video discs (DVD), or videotapes should be listed and retained in accordance with contractual requirements or codes and included with the data sheet.