Methods of sampling of steel for prestressed and reinforced concrete, Part 1: Prestressing steel
1984 Edition

IS 10790 Part 1 (1984) mandates standardized sampling approaches to ensure representative quality testing of prestressing steel. Commonly employed methods include random sampling—where samples are drawn unpredictably from various batches to eliminate bias; composite sampling—combining multiple samples from a batch into one for testing; and incremental sampling—collecting samples at regular stages during production or shipment. The sample quantity and frequency depend on batch size, with typical numbers ranging from one sample for batches up to 50 tons, two for 50 to 200 tons, and three or more for larger batches. Samples should ideally be taken from the midpoint of wires or strands to avoid end effects.

Within IS 10790 Part 1, Acceptable Quality Level (AQL) is defined as the highest percentage of defective items that can be tolerated as an average during sampling inspection (Clause 2.11). The code typically uses an AQL of 2.5% for larger batch sizes, particularly noted in Clause 2.5. Sampling plans specify visual, dimensional, and weight inspection criteria with defined sample sizes and acceptance numbers based on lot size (Table 2). If the number of defective samples identified is equal to or less than the acceptance number, the lot is accepted; otherwise, it is rejected. This systematic approach ensures consistent quality adherence.

While IS 10790 Part 1 focuses mainly on sampling and quality control, standard industry practices and related Indian Standards (such as IS 1786) provide guidance on inspection criteria. For visual inspection, steel should be free from surface defects such as rust, mill scale, cracks, laps, seams, and any irregularities that could compromise performance. Coatings, if applied, must be even and well adhered. Dimensional inspection includes verifying diameter within typical tolerances of ±0.5 mm, confirming length according to specifications, ensuring straightness with minimal bends (generally within 1% of length), and checking strand pitch per manufacturer’s data. These criteria help maintain material integrity and conformity.

Testing physical characteristics under IS 10790 Part 1 involves preparing representative specimens (Clause 4.3.2.1) from items cleared by visual and dimensional inspections. The number of specimens depends on lot size as per Table 3 (not included here). Statistical evaluation (Clause 3.2.2.1) uses methods like means and ranges aligned with IS 7200 and IS 6200 series procedures. For two specimens, both must meet test criteria; for three or more, the lot passes if the mean minus 0.4 times the range equals or exceeds the minimum specification limit. This ensures a statistically valid appraisal of tensile strength, proof stress, elongation, and related mechanical properties.

If a batch does not conform to the requirements specified in IS 10790 Part 1, immediate corrective actions include addressing manufacturing process issues (Clause 3.2.1) and segregating non-compliant materials. Upon purchaser request or in the absence of valid test certificates, detailed lot inspection should be conducted (Clause 4). This involves visual inspection followed by random sampling for dimensional and weight properties based on Table 2 acceptance criteria. Mechanical testing of tensile and related parameters is performed according to Clause 4.3.2.4, with acceptance depending on passing results of 2 or more samples evaluated statistically. Only batches meeting all criteria are accepted, ensuring quality control and compliance.