2.3 Material Condition, Sampling & Visual Examination

2.3 Material Condition, Sampling & Visual Examination

Quick Answer: Beyond reviewing paperwork, inspectors must physically examine steel upon delivery. This involves checking for excessive rust (SSPC Grade D pitting), surface defects (scabs, slivers, seams), and internal flaws like laminations. Dimensional checks must verify that camber, sweep, and warpage fall within ASTM A6 tolerances. If steel loses its traceability or is rejected, formal sampling and physical testing of coupons may be required to qualify the material for use.

Paperwork verification is only half the battle. A structural steel special inspector must also perform a rigorous visual and physical examination of the material as it arrives at the fabrication shop or the erection site. Steel is an industrial product subjected to intense heat and massive mechanical forces during rolling, and physical defects or dimensional variations can occur.

Visual Examination for Surface and Internal Defects

When inspecting newly delivered steel, the inspector should walk the length of the members looking for anomalies that could compromise structural integrity or interfere with welding and bolting operations.

Mill Scale and Rust Grades

Hot-rolled steel leaves the mill coated in a thin, brittle layer of oxidized iron known as mill scale. Over time, exposure to moisture causes the steel to rust. The Society for Protective Coatings (SSPC) and NACE International classify the initial condition of steel into four rust grades:

• Grade A: Steel surface completely covered with adherent mill scale; little to no rust.
• Grade B: Steel surface covered with both mill scale and rust.
• Grade C: Mill scale has rusted away or can be easily scraped off; some slight pitting may be visible.
• Grade D: Mill scale has completely rusted away, and significant, widespread pitting is visible to the naked eye.

Light rust (Grades B and C) is generally acceptable for structural steel and is often preferred before painting, as it provides a rougher surface profile. However, Grade D pitting can reduce the actual cross-sectional thickness of the member. If severe pitting is observed, the inspector must use a micrometer or ultrasonic thickness gauge to verify that the remaining steel thickness still meets the minimum tolerances specified in ASTM A6.

Surface Defects: Scabs, Slivers, and Seams

During the rolling process, impurities or cooling anomalies can create surface defects:

• Scabs: Splashes of molten steel that cool and stick to the surface during casting, then get rolled into the final shape. They often appear as irregular, crusty patches.
• Slivers: Loose, thin pieces of steel rolled into the surface that can peel back like a splinter.
• Seams: Longitudinal crevices or lines on the surface caused by the folding over of metal during rolling that did not completely weld together.

Minor surface defects can often be repaired by the fabricator through light grinding. However, if grinding reduces the cross-section below minimum tolerances, the defect must be completely excavated by grinding and repaired via welding, following strict procedures outlined in ASTM A6.

Laminations and Lamellar Tearing

Laminations are internal, planar defects caused by impurities, slag inclusions, or gas pockets that get flattened out parallel to the surface of the steel plate or flange during rolling. They act as internal delaminations.

Laminations become a critical hazard in highly restrained welded joints, particularly thick tee-joints (e.g., a thick plate welded perpendicularly to the face of another thick plate). As the massive weld cools, it shrinks and exerts tremendous tension perpendicular to the rolled surface of the base metal (the through-thickness direction). If a lamination is present, this shrinkage stress can rip the steel apart internally. This specific type of failure is called lamellar tearing. When inspecting heavy, highly restrained welded connections, ultrasonic testing (UT) is often required prior to welding to ensure the base metal is free of laminations in the weld zone.

Dimensional Checks and Tolerances (ASTM A6)

Steel is rarely perfectly straight. The dimensional tolerances for hot-rolled structural steel are governed by ASTM A6, Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes, and Sheet Piling. The AISC Code of Standard Practice (AISC 303) also references these tolerances.

During visual examination, the inspector should verify the following dimensional parameters:

• Sweep: Curvature of a structural member along its weak axis (bending side-to-side).
• Camber: Curvature of a structural member along its strong axis (bending up or down). Note that beams are often intentionally cambered upward at the fabrication shop to compensate for the dead load deflection of the concrete floor slab.
• Flange Tilt and Warpage: The flanges of a W-shape must remain relatively perpendicular to the web. Excessive tilt or warping can make it impossible to properly seat bolted connections or weld stiffener plates.
• Depth and Width: The overall dimensions must be within a fraction of an inch of the nominal published dimensions.

If a member exceeds ASTM A6 tolerances, it may require heat straightening by the fabricator or outright rejection if the deformation is too severe.

Material Sampling Protocols

In situations where steel arrives without CMTRs, loses its heat traceability markings, or exhibits severe, unexplainable defects, the material is considered "unidentified" or "non-conforming." To qualify this steel for structural use, physical testing must be performed by an independent, accredited metallurgical laboratory.

The inspector plays a vital role in this process by establishing a strict chain of custody. The sampling protocol typically involves:

1. Location Selection: Working with the Engineer of Record to determine where coupons (sample pieces) can be extracted without compromising the member's final structural capacity (e.g., taking samples from the web near the neutral axis, or from excess length that will be trimmed).
2. Witnessing the Cut: The inspector must physically witness the fabricator cutting the coupon from the questionable member.
3. Marking and Custody: The inspector immediately applies a unique identifying mark or tamper-evident seal to both the coupon and the parent member.
4. Laboratory Transport: The coupon is transported to the testing lab along with chain-of-custody documentation.
5. Testing: The lab performs tensile tests (for yield, ultimate strength, and elongation) and spectrographic analysis (for chemical composition).

Only if the laboratory results meet all the requirements of the intended ASTM specification, and the EOR reviews and approves the data, can the previously unidentified steel be incorporated into the project.

Fastener Documentation and Sampling

Material sampling on an S1 project also covers fastener assemblies. RCSC Section 2.1 requires the manufacturer certifications documenting conformance of all fastener components to be available to the engineer of record and the inspector before assembly or erection of structural steel, and AISC 360 Table N5.6-1 makes confirming those certifications a Perform task for quality assurance.

When the project specifications call for independent laboratory testing of bolts, nuts or washers, the inspector's sampling duties mirror those for steel coupons:

1. Select at random from each production lot in the quantity the specification requires, keeping the components of each assembly together.
2. Keep lot identity. Record the bolt, nut and washer lot numbers from the containers and certifications, and never mix lots in one sample.
3. Tag and seal each sample with project, location, lot and date, and start a chain-of-custody record.
4. Arrange transport to the testing laboratory named in the statement of special inspections or the specifications.
5. Check the report against the tests that were specified (for example, proof load, tensile and hardness tests on bolts, proof load on nuts, hardness on washers, coating thickness, and rotational-capacity testing of galvanized assemblies).

Galvanized A325 assemblies are a special case. The RCSC commentary explains that ASTM requires the supplier to assemble a galvanized bolt with its lubricated galvanized nut and washer and test it for rotational capacity before shipment. Galvanized bolts and nuts are therefore treated as a manufactured assembly that must be supplied, tested and shipped together; galvanized bolts and nuts bought from separate suppliers do not meet that intent.

Field pre-installation verification (Chapter 4) is a separate requirement. It checks the assembled components and the installation method in a tension calibrator at the site, and it does not replace laboratory testing that the specifications require.