How To Test The Quality of Low-pressure Boiler Tubes?

Low-pressure boiler tube refers to seamless steel tube used to manufacture low-pressure boilers (pressure less than or equal to 2.5MPa). This type of steel tube is usually made of steel ingots or solid tube billets through perforation, hot rolling, cold rolling or cold drawing. Low-pressure boiler tubes are mainly used to manufacture superheated steam tubes, boiling water tubes, water-cooled wall tubes, smoke tubes and arch brick tubes of various structures of low- and medium-pressure boilers.

The material of low-pressure boiler tubes is usually high-quality carbon structural steel, and the common materials are No. 10 and No. 20 steel. These steel pipes are used to transport low and medium-pressure fluids in industrial boilers and domestic boilers. They have high strength and good plasticity and can meet the use requirements of boilers under different working conditions. So what are the quality standards of these low-pressure boiler tubes? How to conduct quality inspection?

The quality standards of low-pressure boiler tubes mainly include the following aspects:

1. Size and shape

The outer diameter and wall thickness of low-pressure boiler tubes have a clear allowable deviation range. For example, the allowable deviation of the outer diameter D1 is ±1.5%, with a minimum of ±0.75 mm; the allowable deviation of the outer diameter D2 is ±1.0%, with a minimum of ±0.50 mm; the allowable deviation of the outer diameter D3 is ±0.75%, with a minimum of ±0.30 mm; the allowable deviation of the outer diameter D4 is ±0.50%, with a minimum of ±0.10 mm.

‌2. Chemical composition‌

The chemical composition of low-pressure boiler tubes is specified in detail to ensure their mechanical properties and corrosion resistance. For example, the common material is No. 20 steel, which is a high-quality carbon structural steel with a carbon content of no more than 0.17%.

‌3. Mechanical properties

The mechanical properties include tensile strength, yield strength, elongation, etc., to ensure the stability and reliability of the steel pipe under complex working conditions.

4. Metallographic structure‌

The metallographic structure affects the strength and toughness of the steel pipe, and the standard has clear requirements for it.

‌5. Nondestructive testing

Nondestructive testing is used to detect defects inside and on the surface of steel pipes to ensure the quality and reliability of steel pipes.

The methods for testing the quality of low-pressure boiler tubes mainly include the following aspects:

1. Appearance inspection

First, the appearance of the low-pressure boiler tube should be inspected, including the gloss of the outer surface, the flatness of the surface, and the presence of scratches, cracks and other defects. Attention should be paid to checking whether there are problems such as desoldering and corner bending at both ends of the tube, and whether there are abnormal conditions such as depressions and bulges on the tube wall.

2. Dimension detection

Measure the diameter, wall thickness, length and other dimensions of the low-pressure boiler tube. Use measuring tools such as calipers and micrometers to measure and compare with manufacturing standards to check whether they meet the specified size range.

3. Internal inspection

Evaluate the internal quality of the low-pressure boiler tube through fluid or optical detection methods. Fluid detection usually includes testing the flow performance of the liquid or gas in the pipeline to detect leaks, blockages and other problems. Optical detection can use equipment such as endoscopes to observe the welds, edges and corners inside the tube.

4. Chemical composition analysis

By analyzing the physical and chemical composition of low-pressure boiler tubes, it is possible to detect whether the material meets the standard requirements. Commonly used chemical analysis methods include spectral analysis, electron probe analysis, etc.

5. Stress test

By applying a certain stress on the low-pressure boiler tube, it is possible to detect whether the pipe can withstand pressure and maintain the stability of its shape. Commonly used methods include pressure test and tensile test, etc.

Summary

Through the comprehensive testing of the above aspects, the quality of low-pressure boiler tubes can be effectively evaluated. When conducting the test, the relevant standards should be strictly followed, and accurate and reliable testing equipment and methods should be used to ensure the accuracy and reliability of the test results.