456A Blueprint Reading, Weld Symbols & Joint Preparation 3 — Questions and Answers
Question 1: What does a 'section view' on a fabrication drawing show compared to a 'plan view'?
- A section view shows the internal geometry of a part as if it were cut along a specified plane; a plan view shows the external top-down view (Correct answer)
- A section view shows the weld symbol details; a plan view shows the overall layout
- A section view is a detailed enlargement; a plan view shows full scale
- A section view shows dimensions in the Z-axis only; plan view shows X and Y dimensions
Correct answer: A section view shows the internal geometry of a part as if it were cut along a specified plane; a plan view shows the external top-down view
A section view (cross-section) shows what a part looks like if it were sliced along a cutting plane indicated by a section line on the plan view. It reveals internal features, groove geometries, and dimensions that would be hidden in an external view. Section views are essential for understanding joint preparation requirements and weld access in complex structures.
Question 2: What does 'NTS' mean on a drawing and why does it matter for welders?
- Not To Scale — dimensions must be taken from the written dimensions, not scaled from the drawing (Correct answer)
- No Tensile Stress — the weld is compression-loaded only
- Non-Tested Specification — the weld does not require NDT
- Neutral To Shear — weld orientation relative to loading
Correct answer: Not To Scale — dimensions must be taken from the written dimensions, not scaled from the drawing
NTS (Not To Scale) means the drawing has been intentionally or unintentionally reproduced at a different scale. Welders and fabricators must use the written dimension values and never measure from the drawing paper. Scaling a drawing can introduce errors from printing, copying, or digital scaling processes that can lead to incorrect joint preparation or weld sizes.
Question 3: On a structural steel drawing for a connection, what does 'PL 25 × 200 × 600 A36' describe?
- A plate, 25 mm thick × 200 mm wide × 600 mm long, made from ASTM A36 steel (Correct answer)
- A pipe with 25 mm wall, 200 mm OD, 600 mm length, A36 grade
- Plate with 25 kN load rating, 200 mm from centreline, 600 mm span
- Profile length 25, section modulus 200, yield 600 MPa, A36 standard
Correct answer: A plate, 25 mm thick × 200 mm wide × 600 mm long, made from ASTM A36 steel
PL is the abbreviation for plate. The three dimensions are thickness × width × length in millimetres. A36 identifies the material specification (ASTM A36 carbon structural steel, 250 MPa yield strength). This type of notation is standard in Canadian structural steel drawings and tells the fabricator exactly what material to order and cut.
Question 4: What is a 'bill of materials' (BOM) on a fabrication drawing?
- A table listing all components, their material specifications, sizes, quantities, and identifying marks for the fabricated assembly (Correct answer)
- A cost estimate for the welding labour on the project
- A list of required welding consumables and shielding gases
- A schedule of required NDT inspections for the weldment
Correct answer: A table listing all components, their material specifications, sizes, quantities, and identifying marks for the fabricated assembly
The bill of materials (BOM) or parts list is a tabulated schedule on the drawing that identifies every component of the assembly with: item number (matching callout bubbles on the drawing), quantity, description, material specification (e.g., A36, A500 Gr C), and dimensions. It allows the fabrication shop to order materials accurately and track all components during assembly.
Question 5: What does the welding symbol 'melt-through' indicate on a drawing?
- Complete penetration of the root from one side is required, producing a visible bead on the back side (Correct answer)
- The weld has penetrated through the base metal unintentionally (burn-through)
- The weld is to be applied with high heat to ensure deep penetration into the base metal
- The weld must be visually inspected for melt-through depth measurement
Correct answer: Complete penetration of the root from one side is required, producing a visible bead on the back side
The melt-through symbol (a filled semi-circle below the reference line, on the back side of a single-sided weld) indicates that complete penetration from one side is required and that a visible root bead is expected on the back surface. It is used for joints where welding access from only one side is possible but full penetration is required.
Question 6: In a drawing, a weld symbol indicates '3/8 in. fillet weld — 6 in. @ 12 in. staggered'. What does this describe?
- 3/8 in. leg fillet welds, 6 inches long, spaced 12 inches apart on centre, with welds on opposite sides offset (staggered) from each other (Correct answer)
- 3/8 in. welds in groups of 6, spaced 12 inches from the edge
- Three eighths of the joint length to be welded, 6 inches from the start, 12 inches from the end
- 3/8 in. throat, 6 in. wide bead, at 12 in. depth
Correct answer: 3/8 in. leg fillet welds, 6 inches long, spaced 12 inches apart on centre, with welds on opposite sides offset (staggered) from each other
This specifies an intermittent staggered fillet weld: 3/8 in. (about 10 mm) leg size, weld segments 6 inches long at 12-inch pitch (centre-to-centre), with welds on opposite sides of the joint offset by half the pitch (staggered). Staggered intermittent welds reduce heat input and distortion while maintaining structural adequacy for shear flow applications.
456A Blueprint Reading, Weld Symbols & Joint Preparation 3
What does a 'section view' on a fabrication drawing show compared to a 'plan view'?