Quality inspection of large diameter SSAW steel pipe

Based on quality inspection results, large-diameter spiral steel pipes are typically classified into three categories: qualified products, repaired products, and waste products. Here’s how these inspections are conducted.

1. Physical Methods Inspection

Physical inspection involves using certain physical phenomena to measure or test the pipes. This can include various non-destructive testing techniques such as ultrasonic testing, radiographic testing, and magnetic particle testing.

2. Pressure Vessel Strength Test

For pressure vessels, both strength and tightness tests are essential. There are two common types of strength tests:

- Hydraulic Test: This involves filling the vessel with water and applying pressure to check for leaks. It ensures the structural integrity of the vessel and its ability to withstand operating pressures.

- Air Pressure Test: This method is more sensitive and faster than the hydraulic test and does not require draining the vessel afterward. It is particularly suitable for products where drainage is challenging. However, it carries a higher risk compared to the hydraulic test, so appropriate safety measures must be taken to prevent accidents during the test.

3. Hydrostatic Test

Each large-diameter spiral steel pipe undergoes a hydrostatic test to ensure there are no leaks. The test pressure is calculated using the formula P = 2ST/D, where:

P is the test pressure

S is the allowable stress

T is the wall thickness

D is the outer diameter

The test stress is chosen to be 60% of the yield value specified in the corresponding steel strip standard.

4. Surface Inspection

Surface inspection, also known as appearance inspection, is a simple yet widely used method. It is a crucial part of the final product inspection, primarily aimed at detecting surface defects and dimensional deviations of the weld. This inspection is generally carried out visually, using standard templates, gauges, and magnifying glasses. Surface defects often indicate potential internal weld defects.

By following these inspection methods, the quality of large-diameter spiral steel pipes can be accurately assessed, ensuring only qualified products are delivered for use in various applications.