1.1 Sampling of steel for testing

Sampling of steel for testing is the process of selecting and cutting representative pieces from a batch of steel delivered to site or a fabrication yard so that they can be tested in the laboratory to confirm that the whole batch meets the specified grade and properties. Because only a few pieces are tested, the samples must be chosen at random from the right batch, cut without damaging or heating the test zone, clearly labelled and traceable to the delivery and mill certificate. Proper sampling protects the structure from substandard steel and protects the contractor and supplier from wrongful rejection. Example: on a new referral hospital wing, the resident engineer selects reinforcement bars at random from each delivery of Y12 and Y16 bars, has them cut and tagged, and sends them to the materials laboratory before the steel is fixed.

Purpose of sampling steel

• Confirming grade and strength: Tests on samples show whether the steel has the yield strength, tensile strength and elongation stated for its grade.
• Checking compliance with standards: Results are compared with the product standard and project specification.
• Verifying mill certificates: Independent tests confirm the supplier's certificates are genuine and correct.
• Detecting substandard or counterfeit steel: Sampling helps reject undersized, brittle or wrongly marked bars before use.
• Providing records: Test results form part of the quality records for the project.

Types of steel commonly sampled

• Reinforcement bars: High yield deformed bars (Y8 to Y32) and mild steel round bars (R6 to R12) for concrete.
• Welded mesh (BRC): Fabric reinforcement for slabs and walls.
• Structural sections: Beams, columns, angles and channels for steel frames.
• Plates and flats: Used for base plates, gusset plates and connections.
• Wire and strand: Binding wire and prestressing strand.

Sampling tools and equipment

Sampling frequency and sample size

The number of samples is set by the product standard (such as BS 4449 for reinforcement) or the project specification. A common requirement is one set of samples for each batch, cast or given tonnage of each bar size from each supplier, with each set usually containing at least three test pieces so that both tensile and bend tests can be done. Sample lengths must suit the testing machine and test; for reinforcement bars, pieces of about 500 to 1,000 mm are commonly cut, depending on bar size and the tests required.

Steps in sampling steel for testing

1. Identify the batch: Record the delivery note, supplier, mill certificate number, grade and bar size.
2. Determine the number of samples: Apply the frequency in the specification to the quantity delivered.
3. Select pieces at random: Choose bars from different bundles and positions, not just the top or the best-looking pieces.
4. Avoid damaged ends: Do not take samples from bent, rusted, flame-cut or damaged lengths.
5. Cut the samples cold: Use a cut-off saw, bar cutter or hacksaw, never a cutting torch, so the steel is not heat-affected.
6. Measure and check: Cut to the required length and check the diameter and markings.
7. Label each sample: Fix a tag showing project, batch, bar size, grade, date and sample number.
8. Record the sampling: Complete the sampling form and have it signed by the engineer and supplier's representative.
9. Transport and store carefully: Bundle samples straight, protect them from bending and rust, and deliver promptly to the laboratory.

Precautions during sampling

• No heating: Heat from flame cutting changes the properties of the steel near the cut.
• No straightening or bending: Do not bend or hammer samples, as this alters test results.
• Representative selection: Samples must represent the whole batch, not specially selected bars.
• Witnessing: The engineer or an independent person should witness sampling.
• Traceability: Never mix samples from different batches or bar sizes.

Typical sample record

Worked example: number of samples required

Given: A delivery contains 45 t of Y12 bars and 30 t of Y16 bars. The specification requires one set of three test pieces for every 20 t, or part of 20 t, of each bar size.

Y12 sets = 45 ÷ 20 = 2.25, rounded up to 3 sets

Y12 test pieces = 3 × 3 = 9

Y16 sets = 30 ÷ 20 = 1.5, rounded up to 2 sets

Y16 test pieces = 2 × 3 = 6

Answer: 9 Y12 pieces and 6 Y16 pieces, 15 test pieces in total.

Chapter Summary

This chapter covered the essential procedures and considerations involved in carrying out structural steel tests. It began with the importance of proper sampling of steel to ensure representative and reliable test results. The discussion then moved to the variety of steel testing equipment required to perform different assessments accurately. Various steel tests were examined in detail, including tensile tests that measure strength, Brinell and Rockwell hardness tests that determine surface hardness, and bending tests which evaluate ductility. The chapter also explained how to analyze and report the test results effectively to inform engineering decisions. Finally, it emphasized the need for regular maintenance of steel testing equipment to preserve accuracy and prolong service life. Together, these topics provide a comprehensive understanding of how to conduct and manage structural steel testing in practice.