Stainless Steel Pipe Fittings

Knowledges of dished heads

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1 types of dished heads

The dished head consists of a convex dished head, a conical shell, a reducing section, a flat cover and a contracting mouth. Convex dished head includes a hemispherical dished head, elliptical dished head, dished and spherical dished head. From the point of view of force, the convex dished head from the hemispherical dished head is not good, but from the point of view of manufacturing difficulties, gradually manufacturing.

2 manufacturing methods of dished heads

A) small dished head: integral molding;

B) large and medium-sized dished heads: first splicing, forming – the most used, the standard requirements mainly for it;

C) oversize dished head: as a result of transportation and open gear wait for a factor to ask, first be divided into valve formation, the latter group is welded together.

Splice position of 3 dished heads

The splice distance shall be required to be greater than 3 Delta, and not less than 100mm (the weld heat affected zone is a high stress zone, and the chemical composition in the zone will be burnt. Therefore, to avoid high stress zone, the area is related to thickness. According to practical experience, the stress attenuation length is greater than 3 and not less than 100mm. But it is difficult for refrigeration equipment to meet this requirement and has its particularity.

The R at the end of the dished dished head avoids splicing and can reduce the thinness and high stress.

When stitching, only the radial direction and circumferential direction are allowed. Later, large dished heads may cancel this requirement.

Welding joint coefficient of 4 splice dished heads

The dished head shall be spliced and then formed, and the welding seam shall be checked by 100% rays or ultrasonic, and the qualification level will go with the shell of the equipment. Finally, the molding weld detection level, the proportion and the equipment shell same, high waste. Give an example

If the equipment shell is 20% tested, the III is qualified. The dished head joint welding seam and final weld line are also III qualified, and the welding joint coefficient is 0.85;

If the equipment shell is 100% tested, the II is qualified. The dished head joint welding seam and final weld line are also II qualified, and the welding joint coefficient is 1.

Therefore, although the dished head joint inspection of 100%, but the level of conformity is not the same, with the equipment shell go.

But pay attention to the manufacturing process:

The correct approach is: material (crossed) – plate – molding – plate into nondestructive testing

If the test is not done before molding, it is not guaranteed to be qualified after molding. That is to say, nondestructive testing means final nondestructive testing.

Source: China Dished Head Manufacturer – Yaang Pipe Industry Co., Limited (

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Pipe Fittings

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