Ensuring quality and reliability when purchasing steel structure materials is critical for the safety and integrity of any construction project. Here are several steps you can take to ensure that you're getting materials that meet the necessary standards:

1. Specify Quality Standards: Before purchasing, define the quality standards that the steel must meet. This could be based on international standards such as ASTM (American Society for Testing and Materials), EN (European Norm), Chinese Standard or national standards specific to your country.

2. Choose Reputable Suppliers: Work with established and reputable suppliers or manufacturers who have a history of providing high-quality steel. Look for those who are certified by recognized industry organizations.

3. Certification and Compliance: Ensure that the steel you are purchasing has the necessary certifications. For example, in many countries, steel products need to be CE marked, which indicates compliance with European health, safety, and environmental protection standards.

4. Material Testing: Ask for material test certificates (MTCs) for the steel you are purchasing. These certificates should include results from tests such as chemical composition, mechanical properties, and dimensions, which confirm that the steel meets the specified standards.

5. Visual Inspection: Perform a visual inspection of the steel to check for any visible defects such as cracks, corrosion, or distortion. This is a preliminary step to assess the material's condition.

6. Third-Party Inspection: Consider hiring a third-party inspection agency to verify the quality of the materials. These agencies are independent and provide objective assessments of the materials' compliance with standards.

7. Batch Traceability: Ensure that each batch of steel has traceability information. This allows you to trace the steel back to its origin and production details, which can be crucial in the event of a quality issue.

8. Check for Consistency: Consistency in the quality of the steel is essential. Request samples or small batches to test the consistency of the material before making a large purchase.

9. Evaluate supplier’s production process: Understanding the supplier's production processes, such as the source of raw materials, manufacturing techniques, and quality control measures, can give you confidence in the quality of their steel.

10. Consider the Source of Raw Materials: The quality of the raw materials used to produce steel can significantly impact the final product. Make sure the steel is made from high-quality iron ore and other alloys.

11. Warranty and After-Sales Service: A reliable supplier should offer a warranty on their products and provide after-sales service in case of any issues.

12. References and Testimonials: Ask for references or testimonials from previous customers to gauge the reliability of the supplier.

By following these steps, you can significantly reduce the risk of purchasing substandard steel structure materials, ensuring that your construction project will have a solid foundation in terms of quality and reliability.