29 replies to this topic

[kkala]

A locally applied rule of thump suggests valve closing in 5*d s, d=pipe diameter in inches (e.g. for d=10", valve to close in 50 s). This rough preliminary indication is for pipelines within a plant or refinery, needing more detailed examination in "suspected" cases. But what about long distribution pipelines?
Suppose closing a valve at main line, 60 km far from pump discharge; pressure wave velocity (celerity) is estimated at 1200 m/s. Time for pressure wave to travel to the pump and return is 60*2/1.2=100 s. Any closing time shorter than 100 s has same result as a sudden closure. To "smooth" surge, valve closing time should be "preferably several times 100 s" (*). But most probably the valve should not close too late ("after the fiesta"), so a compromise has to be made between closing time and surge pressure through the aid of suitable software. The latter can also help in specifying required protection against developed overpressure...

(there are intermediate posts)

....As far as betting on rule of thumb being found as a practice of some imaginary reputable engineering company, the forum does not encourage gambling. Constantly mentioning local practices and local rules of thumb also indicate half-baked knowledge and the propensity to bluff.
And as you mentioned "nobody has the right to doubt" cannot be accepted. Anyone has the right to question and ask for justification and if the person is honest he or she will accept his ignorance or lack of knowledge and say so.
Since valve closure time has a major impact on the surge analysis let us get the fact right in terms of practices followed by internationally recognized companies instead of saying local rules of thumb. Here is what Shell standards have to say regarding valve closure time.......

- Recommended time of valve closure was not of interest in the specific case. Surge protection would require time longer than what any mentioned practice suggested, if additional antisurge means were not installed. This is indicated in the first post.
- Nevertheless a found recommendation by Mobil suggests an operator actuating speed of 12 in /min for motor operated valves, that is 1 in / 5 sec. This is judged to comply with first post. 1" valve shall close in 5 sec, 2" valve in 10 sec, etc.
- The statement "nobody has the right to doubt" attributed to kkala is false. The opposite is true, as posts No 13 and 15 by kkala say.

Edited by kkala, 16 January 2012 - 06:21 PM.

[kkala]

A locally applied rule of thump suggests valve closing in 5*d s, d=pipe diameter in inches (e.g. for d=10", valve to close in 50 s). This rough preliminary indication is for pipelines within a plant or refinery, needing more detailed examination in "suspected" cases. But what about long distribution pipelines?
Suppose closing a valve at main line, 60 km far from pump discharge; pressure wave velocity (celerity) is estimated at 1200 m/s. Time for pressure wave to travel to the pump and return is 60*2/1.2=100 s. Any closing time shorter than 100 s has same result as a sudden closure. To "smooth" surge, valve closing time should be "preferably several times 100 s" (*). But most probably the valve should not close too late ("after the fiesta"), so a compromise has to be made between closing time and surge pressure through the aid of suitable software. The latter can also help in specifying required protection against developed overpressure...

(there are intermediate posts)

....As far as betting on rule of thumb being found as a practice of some imaginary reputable engineering company, the forum does not encourage gambling. Constantly mentioning local practices and local rules of thumb also indicate half-baked knowledge and the propensity to bluff.
And as you mentioned "nobody has the right to doubt" cannot be accepted. Anyone has the right to question and ask for justification and if the person is honest he or she will accept his ignorance or lack of knowledge and say so.
Since valve closure time has a major impact on the surge analysis let us get the fact right in terms of practices followed by internationally recognized companies instead of saying local rules of thumb. Here is what Shell standards have to say regarding valve closure time.......

- Recommended time of valve closure was not of interest in the specific case. Surge protection would require time longer than what any mentioned practice suggested, if additional antisurge means were not installed. This is indicated in the first post.
- Nevertheless a found recommendation by Mobil suggests an operator actuating speed of 12 in /min for motor operated valves, that is 1 in / 5 sec. This is judged to comply with first post. 1" valve shall close in 5 sec, 2" valve in 10 sec, etc.
- The statement "nobody has the right to doubt" attributed to kkala is false. The opposite is true, as posts No 13 and 15 by kkala say.

Ankur2061 has placed a negative feedback on the above post ~ 3 hours ago. Why? He is kindly requested to explain.
Argumentation is developed there to support kkala's framed post of 17th Dec 2011, versus framed post by ankur2061 of 18 Dec 2011(there were intermediate posts too). The issue has emerged because Mobil's recommendation was found and unnecessary noise on recommended valve closure time should be rightly attenuated. I think kkala' s post objectively deserves no feedback, and this may be more clear by looking into whole thread.

Edited by kkala, 19 January 2012 - 05:09 AM.

[ankur2061]

Please provide the document name, number and revision of the said Mobil Standard and the exact wording mentioned in the Mobil Standard. The valve closure time mentioned according to Shell DEP has been quoted verbatim in my post.

[kkala]

Please provide the document name, number and revision of the said Mobil Standard and the exact wording mentioned in the Mobil Standard. The valve closure time mentioned according to Shell DEP has been quoted verbatim in my post.

OK, Shell practice wording may be exact, but I do not see practice identification in post No 14, and I understand this.
I cannot disclose more on Mobil's practice, probably being proprietary. "Photographic" wording is not judged permissible in the specific case. Given information could be verified by somebody having access to relevant documents. But it has been already noted that recommended valve closing time has no significance on this topic.
Nevertheless "gambling", "half baked knowledge", "propensity to bluff" are significant, even in case of no further evidence. Some further evidence has been searched and found.

Edited by kkala, 19 January 2012 - 07:17 AM.

[sachincheresources]

Can anyone explain the exact basis for not carrying out surge analysis for lines with length less than 100 m length and valve closure time greater than 5 seconds? It is mentioned in older Shell DEP but any theoratical evidence for the same?