API650 - Unstiffened Shell height & Wind Girders
API650 - Unstiffened Shell height & Wind Girders
(OP)
Does API650 allow for taking credit in the Design of Wind girders, when Wind speeds are less than 120 mph? Add-4 has introduced the Velocity consideration in the calculations in 3.9.6, 3.9.7. Wind velocity in my region is 87 mph. The resultant would be comparatively less no. of wind girders and smaller sections, since the ratio (V/120) would be reduced at lower speeds.





RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
Just a reminder about wind speeds. The previous edition of API-650 used a maximum sustained wind speed of 100 mph. The current version uses 120 mph which is the "maximum three-second gust". You should be using the maximum three-second gust wind velocity in the newest version. Roughly, the three-second gust is a bout 20% larger than the max sustaned wind speed.
Joe Tank
RE: API650 - Unstiffened Shell height & Wind Girders
We asked about the pressure resulting from wind and I have attached the answer below. When we received this response from API, we immediately followed up with a clarification request addressing minimum wind velocities as the velocity is used other places. We have not received a response from API on this question yet.
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
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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?
RE: API650 - Unstiffened Shell height & Wind Girders
"
If an API standard is silent on an issue, sound engineering takes precedent.
Best regards,
Gordon
API
Gordon Robertson
1220 L Street NW
Washington , DC 20005
P-202-682-8190
robertsong@api.org
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From: Balu K V
Sent: Saturday, February 10, 2007 1:37 AM
To: Gordon Robertson
Subject: Technical Inquiry to API650 Sec 3.9.7.1
Dear Mr. Gordon,
Background
The Basic Design Wind speed (3 sec gust, 50 year return period) in the region being considered for Tank construction is 87 miles per hour.
Question
Can credit be taken for lesser Wind velocities in the design of Intermediate Wind Girders and calculation of H1 in section 3.9.7.1 of API650 ? Can the Velocity pressure be recalculated for the changed Wind speed ?
If the answer to both above is "NO", the clause could be modified to include the following - "Minimum Wind Pressure for Design of Shells and Wind Girders shall be 36 lbf/sq.ft. No credit shall be allowed for regions where Wind Speeds are less than 120 mph".
I hope API will issue the clarification. "
RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
As I read the current edition and addenda, the adjustsments for differeng wind velocities are now built into each equation. These adjustments are applicable for all wind velocities, not just when it exceeds 120mph (3 sec gust). If you are disappointed with API's maintenance of the inquiries on the website, I suggest that you let them know about that. It would be useful for all of us for them to maintain it in a timely manner.
Joe Tank
RE: API650 - Unstiffened Shell height & Wind Girders
I have done exactly that and have copied Mr. Gordon directly on this thread requesting that a clear statement be made regarding this issue.
RE: API650 - Unstiffened Shell height & Wind Girders
Joe Tank
RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
It looks to me like API has indeed stated that the wind velocity for design is now a valiable to be determined by the purchaser. The purchaser now has the privilaege of specifying a design wind speed may be higher or lower than 120mph. If the purchaser is silent, then the manufacturer simply reports what speed was selected for design. The second approach again gives the purchaser a chance to accept the reported design wind speed or change the contract accordingly. Does anyone know if APi is relooking at the wind speed again?
Joe Tank
RE: API650 - Unstiffened Shell height & Wind Girders
RE: API650 - Unstiffened Shell height & Wind Girders
No, I'm looking at Add 4. The last sentence of 3.2.1 f requires that the manufacturer report the wind speed used for design to the purchaser.
Joe Tank