Bottom Dished Heads

The design of the straight flange section of the dished head is of vital importance for ensuring the safe operation of pressure vessels, so Dingjin suggests you to pay more attention to its value. The main functions of the straight flange section of the dished head are listed as below :

Avoid stress concentration: The setting of straight sections can prevent the circumferential weld seam connecting the head and the cylindrical body from overlapping with the stress concentration area at the edge, thereby reducing welding residual stress and various welding defects.

Improving the stress condition: The straight sections can prevent the sudden change in the radial curvature radius at the connection weld between the head and the cylinder, thereby improving the stress condition of the weld.

Improving structural stability: After the standard elliptical head is connected to the cylinder, the presence of the straight edge section can alleviate the circumferential compressive film stress, enhance the circumferential stability of the head, reduce the stress intensity value of the film, and increase the strength of the head.

Convenient for processing and inspection: The setting of the straight edge section makes the processing of the head, the assembly with the cylinder body, and the non-destructive testing of the weld seam much more convenient.

Production capacity of Dingjin for straight flange is not more than 60mm based on different wall thickness.

Generally, Dingjin has to perform stress-relief heat treatment for bottom dished heads based on below reference information:

When the maximum deformation rate of a cold-formed head exceeds the specified limit (e.g., >5% for carbon steel or low-alloy steel), or when the thickness is ≥13 mm and the carbon steel/low-alloy steel head has not undergone subsequent heat treatment after cold working, such bottom dished heads should be performed stress-relief heat treatment.

After processing, such as hot forming of heads (e.g., heating to 900–950°C for heads with thickness > 50 mm) or after spinning of thick-section low-alloy steel, stress-relief annealing or softening treatment is required to eliminate work hardening.

For pressure vessel heads that may be subject to stress corrosion cracking (e.g., those containing liquefied petroleum gas, anhydrous liquid ammonia, alkaline solutions, etc.), stress-relief heat treatment must be performed after welding regardless of wall thickness.

Carbon steel vessel heads requiring hot-dip galvanizing or aluminizing must undergo stress-relief heat treatment prior to these processes.

When Dingjin manufactures dished heads for pressure vessels, welding quality and standards are crucial to ensure safety and performance. We follow industry-recognized codes such as ASME (American Society of Mechanical Engineers) and GB (Guobiao, China National Standards) to meet diverse requirements.

**ASME Welding Standard**

ASME Section VIII outlines detailed procedures for welding pressure vessel components, emphasizing strict material specifications, welder qualifications, and rigorous inspection methods. This standard is globally recognized for ensuring high reliability in pressure equipment.

**GB Welding Standard**

GB standards provide comprehensive guidelines tailored to Chinese market needs, focusing on material compatibility, welding techniques, and testing methods. GB standards ensure product quality and compliance within China and many international markets.

Dingjin can offer welding solutions according to ASME or GB standards based on your project's origin, regulatory demands, and application needs. Both standards maintain high quality and safety, ensuring excellent performance of welded heads.