To determine the appropriate processing allowance for seamless pipes, it's crucial first to understand the product's dimensional tolerance range. Dimensional tolerance refers to the allowable deviation from the actual size of a product, ensuring variations remain within acceptable limits for interchangeability and coordination between products.
The tolerances of seamless pipes vary significantly depending on their use, production methods, and equipment. Professional skill levels of technicians also impact tolerances. When determining machining allowances, fully understanding the product's production performance and guaranteed tolerance range is essential. Specific problems should be analyzed in detail.
Reserved Dimensions for Seamless Steel Pipe Processing
Precision Seamless Steel Pipes:
General inner and outer diameter tolerances are ±0.1mm, with special requirements down to ±0.025mm. A machining allowance of more than 0.2mm for grinding is recommended. Confirm with the manufacturer based on actual tolerance data.
Ordinary Hot-Rolled Seamless Pipes:
The national standard GB/T 8162-2018 for structural seamless steel pipes allows for an outer diameter tolerance up to ±0.5mm. A single-sided machining allowance of 0.7mm or more is recommended for turning.
Manufacturer Communication:
Communicate and coordinate with the manufacturer to determine the most appropriate processing allowance, considering all factors to ensure quality and accuracy.
Ovality in Seamless Pipes
Definition and Measurement: Ovality refers to the difference between the maximum and minimum diameters of a seamless pipe section, expressed as D/d. It is typically measured using the three-point method or the auxiliary circle method.
Factors Affecting Ovality:
Rolling Process and Equipment:
Insufficient or excessive rolling passes can lead to increased ovality.
Material Quality:
Defects such as pores or inclusions can cause surface irregularities, impacting ovality.
Pressure Roller Wear:
Wear of pressure rollers used to adjust ovality during rolling affects the pipe's geometry and ovality.
Ovality Standards:
International Standards (ISO):
Ovality should be within 10% of the sum of the pipe diameter and wall thickness.
American Standards (ASTM):
Ovality is 1% of the difference between the outer diameter and the inner diameter.
Japanese Standards (JIS):
Ovality should not exceed 0.5% of the diameter.
Chinese National Standards:
The maximum ellipticity error allowed is ±8% of the sum of the pipe diameter and wall thickness.
Summary:
Ovality is a critical factor affecting the quality of seamless pipes. Adhering to relevant standards and eliminating factors that cause ovality can ensure the production of high-quality seamless pipes.
United Steel Industry As the most important steel pipe manufacturer and exporter in China, in the past 20 years, we have completed more than 100 projects, with partners in more than 100 countries, and established relationships with oil and gas and EPC companies in many countries business relationship.
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