Spiral steel pipes must undergo mechanical property tests, flattening tests, and expansion tests prior to shipment, and must meet the requirements stipulated by the standards. The quality inspection methods for straight seam steel pipes are as follows:
1. Surface inspection, or visual examination, is a simple and widely-used inspection method, an important part of finished product inspection. It mainly detects surface defects and dimensional deviations in weld joints. Generally, it is conducted by the naked eye, with the aid of standard templates, gauges, and magnifying glasses. If defects appear on the weld surface, there is a possibility of defects within the weld itself.
2. Physical Method Inspection: Physical inspection methods involve using various physical phenomena to measure or examine. The examination of internal defects in materials or workpieces is generally conducted using non-destructive testing techniques. Non-destructive testing includes ultrasonic testing, radiographic testing, penetrant testing, and magnetic particle testing.
3. Strength Testing of Pressure Vessels: In addition to密封性试验for pressure vessels, a strength test is also required. The common tests include hydrostatic and pneumatic tests. Both can verify the tightness of welds in containers and pipes under pressure. The pneumatic test is more sensitive and quicker than the hydrostatic test, and the product does not need to be drained after the test, making it particularly suitable for products that are difficult to drain. However, the risk of the test is greater than that of the hydrostatic test. It is necessary to adhere to the corresponding safety technical measures during the test to prevent accidents.
4. Denseness Inspection: For welded containers storing liquids or gases, the non-denseness defects in the welds, such as penetrating cracks, blow holes, slag inclusions, incomplete fusion, and loose structures, can be detected through denseness tests. Methods of denseness inspection include kerosene test, water-filled test, water jet test, etc.
5. Hydrostatic Test - Each steel pipe should undergo a hydrostatic pressure test without any leakage, and the test pressure is calculated as P = 2ST/D. Here, S is the test stress in the hydrostatic test in MPa, and the test stress for the hydrostatic test is selected at 60% of the minimum yield strength specified by the corresponding steel strip standard (Q235 is 235 MPa). Stability Time: Spiral welds of steel pipes used for fluid transmission should be subject to random X-ray or ultrasonic inspection (20%).
Based on the quality inspection results of spiral steel pipes, they are typically categorized into three types: qualified products, repaired products, and scrap. Qualified products refer to spiral steel pipes that meet the relevant standards or delivery acceptance technical conditions in terms of both appearance and intrinsic quality; repaired products are those that do not fully meet the standards and acceptance criteria in terms of appearance and intrinsic quality but are allowed to be repaired, and can reach the standards and acceptance conditions after repair; scrap products are those that do not meet the standards in terms of appearance and intrinsic quality, and are not allowed to be repaired or still do not meet the standards and acceptance conditions after repair.
Scrap is categorized into two types: internal and external. Internal scrap refers to the waste spiral steel pipes found within the foundry or casting workshop; external scrap refers to the waste spiral steel pipes discovered after delivery, usually revealed during mechanical processing, heat treatment, or use, and the economic loss it causes is much greater than that of internal scrap. To minimize external scrap, spiral steel pipes produced in batches undergo trial heat treatment and rough processing as samples before shipment, in an effort to identify potential defects in the spiral steel pipes within the factory, so that necessary remedial measures can be taken early on.
