The medium in this pressure vessel is chlorine; a DN133 pipe is welded into an opening on the flat cover. According to the safety regulations for fixed-pressure vessels, is a fully penetrated structure required?

Chlorine is a toxic substance, and generally, pressure-containing structures for such substances require high standards regarding welding quality. According to conventional understanding, when welding nozzles are installed in flat covers, if the medium is highly hazardous or highly toxic, regulations generally require a fully penetrated structure to ensure a secure seal and avoid the risk of leaks. However, regarding the welding of this specific DN133 fitting to the DN400 flat cover, it is necessary to refer to the specific provisions in the codes concerning hole reinforcement and weld joint design, as well as the design conditions (such as design pressure, temperature, fatigue conditions, etc.). It is recommended that you refer directly to the relevant articles in the \"Safety Technical Inspection Regulations for Fixed Pressure Vessels,\" or consult a qualified design firm. After all, since this involves safety standards, it’s better not to draw conclusions lightly if you’re not sure about them

The DN133 connection on the flat cover of this pressure vessel and its weld joint to the shell must adopt a fully penetrated structure. Chlorine is a highly hazardous substance. According to the \"Regulations on Safety Inspection of Fixed Pressure Vessels\" (TSG 21-2016), for pressure vessels that contain substances with extremely high or high toxicity, the weld joints between the nozzles and the vessel body must be of a fully penetrated design.

The second floor is the correct answer, namely as stipulated in Clause 3.2.2.2 of the Fixed Capacity Regulations

Full penetration is required; it’s explicitly stipulated.

This post was last edited by Zhang Junli on 2026-7-3 at 15:22. Everything posted must be reviewed; the original post has been modified to require a fully welded structure, but structures that are not fully welded are also permitted. This is a misconception that many people have. A fully penetrated structure refers to the design form of the welded joint, while incomplete penetration is a type of defect; the two refer to different things.

Under-welding is allowed to exist, but isn’t it immediately deemed defective? It’s just that small fittings are not currently required to undergo radiographic or ultrasonic testing

The fully penetrated structure mentioned by the original poster and the underpenetrated condition you mentioned are two different things.

The wording above is incorrect; one should use the terms \"fully penetrated structure\" and \"partially penetrated structure,\" which refer to the structural forms of welding joints. What you mentioned as \"incomplete penetration\" refers to a type of defect.