API 653 Emergency Venting Requirements

Tankarator · Sep 16, 2024

Hey all,

I am a relatively new API 653 inspector (originally certified in 2021) and have recently been delving into the requirements for emergency venting for tanks that are inspected under API 653. Many of the tanks I have inspected are old (circa 1960) and lack original design or fabrication records. Additionally, many of these tanks are less than 50' in diameter and either do not possess any emergency relief devices or have something small such as a 10" Morrison Brother Figure 244. As such, it is difficult to determine whether these designs were "code compliant" at the time of construction.

Regardless, under the current edition of API 653 (2020), section 9.12.1.1 states that, "Roof repairs involving tank venting shall be made such that normal and emergency venting meet the requirements of API 650, Section 5.8.5".

Following through with API 650 section 5.8.5 involves significant work including determining tank roof frangibility, field verifying tank design, estimating material weights, calculating allowable pressures in accordance with Appendix F, calculating appropriate venting capacities in accordance with API 2000, etc.

Is it the intent of API 653 that all existing tanks inspected under the standard comply with the current emergency venting requirements of API 650 and API 2000?
I cannot imagine that that is the intended interpretation, but I also cannot find a caveat that would allow you to interpret it differently, especially for tanks that do not possess dedicated emergency relief devices and whose frangibility is dubious.

These tanks have been in service for 80+ years without issue, so I don't want to be the guy that makes them add a stuff for no reason. But, if they are non-compliant then they are non-compliant.
Am I incorrect or missing something in my interpretation?

Any input would be appreciated.
Thanks,

IFRs · Sep 16, 2024

I think you read API 653 correctly and there is no "out" for old equipment that has not failed yet. If you have found a potentially dangerous situation or weakness in a design feature it is your responsibility to let the owner know. The conditions that the tank is exposed to may have changed in 80 years, there may be more people nearby, there may be waterways not there before, there may be other tanks not there before, the local rules may have changed, there is now an EPA, clean air and clean water rules, etc. Just because it has been OK for 80 years does not mean it will be OK for 80, 60, 20 or 1 more. If you are making repairs that involve the venting, it just makes sense to upgrade the vents to current code. If you are not repairing the venting, you 'could' leave it alone but I would run the numbers (not all that hard actually) or get someone to run the numbers so you know if the venting meets current code. Then inform the owner and let them decide if they want the risk. If you or they feel secure and comfortable standing in front of a judge saying "we did not check the tank for emergency venting" or "we checked the tank for emergency venting and if failed but we did nothing" and we are very sorry for the injury, loss of life or environmental damage our tank caused but we really want you to find in our favor. If you are a registered PE your first duty (at least in the states I'm licensed in) is to the public safety. Delivering news that an owner may have to spend money to remain in compliance and continue to make money on their old equipment is just part of the job. My opinion only.

JStephen · Sep 16, 2024

To complicate the situation, the rules defining frangibility and the rules for calculating allowable pressure have been updated a number of times through the years. Anchor bolt embedment design has also changed through the years. So if you take a random old tank and apply current rules to it, there is a good chance it will no longer be adequate for the original design pressure. Or may have been built as "frangible" but no longer is.
I believe API-12F, API-12D, and UIL have their own definitions of "frangible" which of course conflict with API-650.

IFRs · Sep 16, 2024

For API 12C tanks circa 1960, API 12C 15th edition 1958 includes this language regarding frangibility in the roof design section of the standard.

API_12C_15th_1958_Column_Suppored_Cone_Roof_Note_re_Frangibility_df46ty.jpg

It would appear that you are on the right track, although the current standard has more details, requirements and restrictions. If you are inspecting to API 653 at the direction of the owner, you really have no choice but to run the numbers and report the results.

Frangibility can be totally ignored (or dealt with if it fails the review) if you replace a cone roof manway with a cover that blows off under the light pressure needed to protect the tank, if a suitably sized one exists). Among others is this one:

https://www.protectoseal.com/product/vapor-and-flame-solutions/emergency-pressure-vents/series53300/

(I have no connection to this company just did a google search).

Is the exising vent suitable to protect for vacuum if it is clean and maintained?

API 650 1st edition took over in 1961, you can get copies of these historical editions from API for a nominal cost.

Tankarator · Sep 16, 2024

Thanks for the replies. Out of an abundance of caution, I have been recommending that they install emergency vents in these tanks. Per my state's regulations and as guided by API 653, these tanks must undergo in in-service inspections every 5 years and an out-of-service inspection every 10-20 years (depending on condition). It just seems odd to me that no previous inspectors ever made mention of emergency venting in their reports. Perhaps it was just an oversight on their part unless maybe they deemed that since no specific roof repairs were being performed, the requirement was not applicable?

The normal pressure and vacuum venting capacities are sufficient per API 2000 calcs, so I do not have any concerns there. There are roof manways, and they would be adequately sized to have blow-off lids. However, many of these tanks have nozzles that were welded into the bolt-on cover plates (such as nozzles for pressure/vacuum vents, mechanical level gauges, etc). All these appurtenances obviously inhibit using the manway for emergency relief.

JStephen · Sep 17, 2024

"Is it the intent of API 653 that all existing tanks inspected under the standard comply with the current emergency venting requirements of API 650 and API 2000?"

In 4.1.1, "When the results of a tank inspection show that a change has occurred from the original physical condition of the tank, an evaluation shall be made to determine its suitability for continued use".
Or, in 4.2.4.5, "Effects of change in operating condition (including product service and pumping rates) on normal and emergency venting shall be considered."
Absent either of those conditions, then in 4.2.4.5.2, "Vents shall be inspected for proper operation and screens shall be verified to be clear of obstruction."

So I would say that normally, it is not the intent to re-evaluate every tank for flow rates, pressure, frangibility, etc.
An owner could re-evaluate for these and other conditions as much as they desired to do.
Fire and building codes could potentially require retroactive work on tanks.

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