Accident caused by too long stud

The stud can’t be screwed

Workshop workers call:
“Can you come here for a moment? The length of the flange stud of one reactor is too long to screw the nut.”
Designer: “if it’s ugly, it’s hard to see. What’s impossible to twist?”
Worker: “just come and have a look.”

As soon as the designer looked at the workshop, he understood:

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The flange of the equipment is equipped with B-type stud of Nb/T 47027-2012.

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When the designer calculates the stud length of equipment flange, the margin is relatively large.
In the process of equipment flange design, the thickness of flange is optimized, but the corresponding stud length is forgotten.
B-type stud is too long, and the consequence is more serious than that of full thread stud. There is a section of bare rod without thread in the middle, which can’t screw the nut.
Due to the delivery in a few days, it was found that the stud was too long by the hydrostatic test!
Re purchase, the delivery date is very certain.
Contact the owner and try to add a thick washer so that the nut can be screwed.

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The scheme was ruthlessly rejected by the owner.
Finally, this stud can only be scrapped and re purchased, resulting in heavy losses.

Error analysis

The reason for this error is very simple, but it is very common – one content has been changed, but the associated content has not been completely changed.
Most of the time, the stud is just a simplified drawing of the center line on the drawing, which is difficult to show intuitively. The ABC type stud of the equipment flange is shown in the figure below.

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Some designers do not draw according to scale, and have no concept of size coordination, so this kind of problem is often encountered.
Is there a better way to reduce this problem?

Drawing stud nut assembly with program

If the stud style can be drawn automatically, there may be a certain probability to avoid this problem.
Is it possible to program the components of stud bolts?
After thinking, the following program is designed:

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By selecting two points, the 1:1 drawing of the assembly of stud nut washer is completed.
The results are as follows
Type A stud:
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Type B stud:

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C type and full thread stud:

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Using the simplest method to draw the stud nut assembly and express the stud vividly can remind the designer that the length of the stud must be paid attention to for type B stud.
Because, type B thread.

Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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