456A Weld Quality Inspection, Testing & Occupational Safety 3 — Questions and Answers
Question 1: What is the '10% RT' inspection requirement for pipeline girth welds under CAN/CSA Z662 and how are the welds selected?
- 10% of all girth welds by a specific welder must be radiographically tested; if defects exceed limits, additional welds by that welder are tested (100% if rejection rate is high) (Correct answer)
- The first 10 welds of every day must be radiographed
- 10% of each type of fitting connection must be tested by RT
- 10% of the linear weld length must be tested; the selection is random
Correct answer: 10% of all girth welds by a specific welder must be radiographically tested; if defects exceed limits, additional welds by that welder are tested (100% if rejection rate is high)
CAN/CSA Z662 requires a minimum of 10% of each welder's girth welds to be RT-inspected. Selection includes welds at highest-consequence locations (road crossings, water crossings, etc.) plus random selection. If defect rates are high, the inspection percentage escalates toward 100%. This per-welder tracking ensures that welder performance is monitored and poor-quality welding is caught early.
Question 2: What is 'time-of-flight diffraction' (TOFD) ultrasonic testing and what is its primary advantage?
- Uses the diffracted signals from defect tips (rather than reflection) to accurately measure defect height/depth; provides more accurate sizing of planar defects than conventional UT reflection techniques (Correct answer)
- A time-based ultrasonic method that measures crack growth rate during service
- A phased array technique that uses time gating to filter out surface echoes
- A contact UT method that measures wall thickness reduction from corrosion
Correct answer: Uses the diffracted signals from defect tips (rather than reflection) to accurately measure defect height/depth; provides more accurate sizing of planar defects than conventional UT reflection techniques
TOFD uses two probes (transmitter and receiver) placed on either side of the weld. Instead of measuring reflected amplitude, it measures the time of flight of diffracted signals from defect tips. This provides very accurate defect height sizing (important for fracture mechanics fitness-for-service assessments). TOFD is accepted by CSA Z662 and offshore codes for pipeline girth weld inspection in combination with PAUT.
Question 3: What is a 'fitness-for-service' (FFS) assessment under API 579 / CSA Z662 Annex K and when is it applied to welded structures?
- An engineering analysis that evaluates whether a component with known defects or damage can continue in safe service, possibly with reduced pressure rating or operating limits, rather than requiring immediate repair (Correct answer)
- A pre-weld assessment to determine whether a particular filler metal is suitable for the service conditions
- A post-weld heat treatment evaluation confirming residual stress levels meet service requirements
- An annual regulatory inspection to verify a pressure vessel remains certified for its rated pressure
Correct answer: An engineering analysis that evaluates whether a component with known defects or damage can continue in safe service, possibly with reduced pressure rating or operating limits, rather than requiring immediate repair
Fitness-for-service (FFS) assessment is applied when inspection reveals defects exceeding the original code acceptance criteria. Instead of automatic rejection, a fracture mechanics-based analysis (using defect dimensions, material toughness, stress levels, and service conditions) determines whether the component can continue in service, possibly with operational restrictions. This avoids costly repairs when remaining life is demonstrably adequate.
Question 4: What is the purpose of 'impact testing' (Charpy V-notch) of weld procedure qualification coupons per CSA W47.1?
- Verifies that the weld metal and HAZ have adequate toughness (notch ductility) at the specified minimum service temperature to prevent brittle fracture (Correct answer)
- Measures the fatigue resistance of the weld under dynamic loading
- Evaluates the tensile strength of the weld metal at low temperature
- Determines the maximum allowable operating pressure for the welded component
Correct answer: Verifies that the weld metal and HAZ have adequate toughness (notch ductility) at the specified minimum service temperature to prevent brittle fracture
Impact testing per CSA W47.1 (and ASME Section IX supplementary essential variables) measures the energy absorbed by the weld metal and HAZ specimens at the specified minimum service temperature. Minimum energy values (e.g., 27 J at -20°C) confirm the procedure produces weld joints with adequate toughness for the design service conditions. Impact qualification is required for most Canadian structural and pressure vessel work.
Question 5: What does the term 'linear indication' mean in dye penetrant or magnetic particle testing?
- An indication (flaw signal) with a length greater than three times its width; typically indicates a planar defect such as a crack and is generally rejectable (Correct answer)
- Any indication that runs parallel to the longitudinal axis of the weld
- A continuous porosity chain aligned along the weld centreline
- An indication caused by the testing equipment itself (false positive)
Correct answer: An indication (flaw signal) with a length greater than three times its width; typically indicates a planar defect such as a crack and is generally rejectable
A linear indication in PT or MT is defined as one where the length is at least three times the width (length ≥ 3W). Linear indications are associated with planar defects (cracks, lack of fusion) and are considered inherently more damaging than rounded indications (pores, inclusions). Most codes treat any linear indication in weld metal as rejectable regardless of size due to the fracture mechanics implications of crack-like defects.
Question 6: What is a 'certified welding inspector' (CWI) certification and what body grants it in Canada?
- The Canadian Welding Bureau (CWB) certifies CWIs; a CWI is qualified to inspect welds, evaluate conformance to codes, and sign off on weld inspection records (Correct answer)
- The Canadian Standards Association (CSA) directly certifies all welding inspectors
- The provincial safety authorities (TSSA, ABSA) certify welding inspectors for pressure vessel work only
- Individual companies certify their own inspectors under ISO 9001 QMS systems
Correct answer: The Canadian Welding Bureau (CWB) certifies CWIs; a CWI is qualified to inspect welds, evaluate conformance to codes, and sign off on weld inspection records
In Canada, the Canadian Welding Bureau (CWB) certifies welding inspectors under the CWB Level 1, Level 2, and Level 3 (Senior) inspector designations. CWB certification is recognized by provincial authorities (ABSA, TSSA, BC Safety Authority) for pressure vessel and structural steel inspection. The AWS CWI (American Welding Society Certified Welding Inspector) is also widely recognized in Canadian industrial work.
456A Weld Quality Inspection, Testing & Occupational Safety 3
What is the '10% RT' inspection requirement for pipeline girth welds under CAN/CSA Z662 and how are the welds selected?