Calculation of p in 3.9.7.1 1

[jaydees]

In 3.9.7.1 a. there is a formula for calculating the velocity pressure p to then be compared to 36 psf as noted in d. This is then to be used to determine H1. If the V is 115 mph, should the value of V used to calculate p be 115 or 120? In d it says that you do this when other factors are specified by the purchaser that are greater than the factors in items a-c. It seems to me you would use the factors specified by the purchaser and if this exceeds 36 psf then you apply the reduction factor.

 

[Bobfromoh]

I think you are referencing an old version of API. The wording is different in the latest edition (11th, June 2007)

 

[jaydees]

The 11th edition is 5.9.7.1 but the wording is essentially the same. Note d stills says the same thing and so my question still remains. Do you only use values that are higher than what was in paragraph a? So if the velocity is 115 mph do you use 120 or 115 mph? Likewise, Kz was used as 1.04. If you have a shorter tank and Kz is less than 1.04 which do you use? It would seem to me that if you have any values that are greater than shown in a that you would use all of the values for the design you are doing and divide it by 36 psf. If this is less than 1 you use 1. Otherwise you use the factor determined.

 

[LeonEarle]

We have asked this question of API 650. Below is the response.


From: Gordon Robertson [Robertsong@api.org]
Sent: Tuesday, November 14, 2006 12:13 PM
To: John Walters
Subject: RE: API 650, Tenth Edition, Addenda 4, Paragraph 3.9.7.1 Note d.
FW: API 650, Tenth Edition, Addenda 4, Paragraph 3.9.7.1 Note d. Page 1
11/6/2007

John,
36 psf is the minimum.

Best regards,
Gordon
API
Gordon Robertson
1220 L Street NW
Washington, DC 20005
P-202-682-8190
robertsong@api.org

From: John Walters [mailto:Jwalters@ptctanks.com]
Sent: Thursday, October 26, 2006 12:09 PM
To: Gordon Robertson
Subject: FW: API 650, Tenth Edition, Addenda 4, Paragraph 3.9.7.1 Note d.

Background Section; The purpose of this inquiry is to obtain an interpretation of the standard.

Main Section;
When other factors are specified by the purchaser that are less than the factors in items a-c, is the total load on the shell to be modified by increasing H1 by the ration of 36 psf to the modified total pressure, or is 36 psf the minimum load to be
applied?

Thank You,
John E. Walters
John E. Walters
Engineering Services Manager
Pasadena Tank Corporation
jwalters@PTCTanks.com
281-457-3996 ext. 145