How to identify the quality of large diameter spiral welded pipe?

Spiral welded pipes are produced by rolling low-carbon or low-alloy structural steel strips into a tubular form at a specific helical angle, also known as a forming angle. These pipes are referred to as spiral tubes or spiral bodies. The outer diameter of these spiral tubes is approximately 30 nanometers, with an inner diameter of about 10 nanometers, and the pitch between adjacent spirals is around 11 nanometers.

To ensure the quality of large-diameter spiral welded pipes, several inspection methods can be employed:

Physical Inspection Method:

This involves using physical phenomena to measure or inspect the pipes. Techniques like ultrasonic testing, radiographic testing, and magnetic particle inspection fall under this category.

Pressure Vessel Strength Test:

In addition to leak tests, pressure vessels need to undergo strength tests. Common methods include the hydrostatic test and the air pressure test. These tests examine the weld tightness of vessels and pipes operating under pressure.

The air pressure test is more sensitive and faster than the hydraulic test. It also eliminates the need for draining the pipes after testing, making it ideal for products where drainage is difficult. However, it carries a higher risk compared to the hydrostatic test, necessitating strict adherence to safety protocols to prevent accidents.

Hydrostatic Test:

Every large-diameter spiral welded pipe must pass a hydrostatic pressure test without any leakage. The test pressure (P) is calculated using the formula: P=2STDP = \frac{2ST}{D}P=D2ST.

In this formula:

SSS represents the test stress (Mpa) for the hydrostatic test, typically chosen as 60% of the yield value specified in the relevant steel strip standard.

TTT is the wall thickness.

DDD is the outer diameter of the pipe.

Surface Inspection:

Visual inspection is a simple and widely used method for assessing the pipe's quality. It is an important part of the finished product inspection and aims to detect surface defects and dimensional deviations.

Inspections are generally carried out with the naked eye, often with the aid of standard templates, gauges, and magnifying glasses. Surface defects may indicate potential internal weld defects, necessitating further investigation.

By applying these methods, the quality of large-diameter spiral welded pipes can be effectively assessed and ensured, guaranteeing their performance and reliability in various applications.

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