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Characteristics of cold-formed heads
Cold-formed heads have accurate dimensions and constant quality, with no surface roughness or oxidation caused by heating, and an aesthetically pleasing appearance. Furthermore, concerns about material degradation due to heating are addressed.
Characteristics of cold-formed heads:
Cold-formed heads have accurate dimensions and constant quality, with no surface roughness or oxidation caused by heating, and an aesthetically pleasing appearance. Furthermore, concerns about material degradation due to heating are addressed.
To assure customers of the reliability of our head products, the materials used are sourced directly from steel mills that smelt and roll steel plates in accordance with the specific specifications for cold-formed heads.
Based on the characteristics of cold-formed heads, some issues require attention. Here, we present some representative examples for your understanding.
About Stress Corrosion Cracking (SCC)
Residual stress and cold work hardening are inherent in cold-formed products, including heads. In the presence of installation stress, welding residual stress, or thermal stress in the container, stress superposition will occur. When utilized in environments prone to stress corrosion, stress corrosion cracking may occur within a short time.
If the material is carbon steel, cracking will occur in the environment of nitrate, ammonia, alkaline sodium, etc.; if it is austenitic stainless steel, cracking will occur in a specific environment with chloride ions, and such cracking is called stress corrosion cracking.
As we are not aware of the design and operating conditions of various boiler pressure vessels for our customers, if the heads you order are intended for use under the aforementioned conditions, please consider methods to eliminate residual stress, select appropriate materials during the design phase, and specify these in the “Contract for Custom Head Manufacturing” to facilitate the adoption of necessary processes to eliminate residual stress and meet design requirements.
About HDG Coating Crackin
When containers made of carbon steel and low-alloy steel are submerged in hot-dip galvanizing or aluminizing solutions, cracks may occur on the straight edge section of the head, a phenomenon termed “galvanizing (aluminizing) brittle crack”. This occurs due to the diffusion of zinc or aluminum, both of which are low-melting metals, towards the crystal boundaries amidst the presence of welding and processing residual stresses. Therefore, prior to hot-dip galvanizing or aluminizing, the container must undergo heat treatment to eliminate residual stress.
About Plastic Working Marks on Carbon Steel Head
When carbon steel is subjected to tensile deformation, a slip line emerges at a 45-degree angle to the principal stress axis, causing the oxide film on the material’s surface to peel off or separate along it.
In the vicinity of the small r-section in the transition area of the cold stamped head, traces of oxide film peel-off form a grid-like pattern, representing surface marks due to plastic working. This is not a harmful defect in any way.
About Plastic Working Marks on Stainless Steel Weld Seam
When the head contains weld seams, prior to stamping and forming, it is imperative to remove all seams from the inner surface of the disk, as well as the weld reinforcement from the straight edge section and transition zone on the outer surface, before proceeding with further processing. Conversely, before spinning and forming, the weld reinforcement on both the inner and outer surfaces of the weld seams must be completely eliminated.
Due to the strength disparity between the weld seam and the base material, stainless steel heads exhibit a slight concavity centering on the weld seam. During plastic working, a slight linear concavity will be generated, which is a superficial trace attributable to the plastic working and not the harmful defects such as cracks.
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Tel: +86-0510-87849500
Fax: 0510-87849507
Address: 198 Wanyuan Road, Wanshi Town, Yixing City, Jiangsu Province
Zip Code: 214212
E-mail: jzftdz@jzftdz.cn
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