Once more about hydrotest pressure

[VladIv]

I thank all the colleges who replied to my question concerned the lowest stress ratio for calculation of the test pressure value (fizza453, mk3223, prex). But to my mind, the HIGHEST ratio should be used. I think, the material which has the lowest stresses ratio is affected by the temperature rise at the least extent and is, consequently, the strongest among the others in the vessel structure. On the contrary, the material with the highest ratio is the weakest one. So, when using the lowest stresses ratio for the calculation of the test pressure value we obtain its lowest value. Moreover, the LOWEST ratio value does not take account of the presence of the weaker materials in the vessel structure at all. As I see, we all think that the stress ratio is introduced into the test pressure value calculation formula with the aim to expose during the test the vessel structure weakest material to the pressure adequate of its operating condition. But, in my opinion, the ratio must be HIGHEST. Please, tell me if my considerations are wrong.

 

[TGS4]

You are incorrect.

However, if you are overwhelmingly convinced that you are correct (and hence that I am wrong), then you are more than welcome to come to the ASME Code Committee meetings and explain to the Code writers that they're wrong and you're right. The contact information for the Code Committees are in the front matter of each book.

See - that's how the community works. Someone comes up with a better idea, convinces the appropriate people of a better way to do things, and gets the changes implemented.

 

[DSB123]

VladIv,
Think about it. If you based the test pressure on the highest stress ratio of a part then by using that pressure the parts with the lower stress ratios would be overstressed would they not???

 

[VladIv]

Mr. TGS4, thank you for the reply. To my regret, I don`t know English well enough to exclude the idea that you are making fun of me. I am simply looking for the reason of the Code such a requirement.

 

[VladIv]

Mr DSB123, if I used the highest stress ratio the parts with lower ratio would not be overstressed because they are stronger than the others. As I have understood it seems wrong to admit that stronger materials have lower stress ratio (stronger here = less affected by the temperature influence, i.e. don`t decrease their properties). Thank you.

 

[TGS4]

VladIV - I am not making fun of you and am not being sarcastic. What I have described is exactly how the Code operates. It's been successfully accomplished before.

What I suggest is that you create some examples, using a wide variety of materials (room-temperature S varies between 6ksi and 30ksi) with a wide variety of stress ratios (from 1 to 6). For each example, calculate design pressure at the design temperature. Then, calculate the test pressure (using either the lowest stress ratio or the highest stress ratio). Then, calculate the stress in each material due to the test pressure at room temperature. Assume that there are only cylinders to simplify the stress calculation process. Finally, report the results.

 

[DSB123]

VladIv,
It's obviously a language problem so it's not worth the effort on my part to try and educate you

 

[VladIv]

Dear Mr. TGS4 and Mr. DSB123, thank you very much for the attention to my question and the time spent for me.
Dear Mr. TGS4, I shall probably follow your advice if I can’t find any convincing explanations of that requirement. As I can see you are a versatile specialist in many fields of mechanics and other sciences and are ready to share your knowledge with other people. I’m sure you know the answer to the question which troubles me for a long time. Please, answer if it is correct to say “strength check of the vessel FROM action of internal pressure”. I mean the use of the preposition FROM. I don’t like it, but I don’t know the correct version. Last year I had to translate some calculations from Russian and asked a similar question here on the language forum, but received no clear answer. Thank you in advance!