Atmospheric Storage Tank - Code Requirements for Access/Egress

[LSUengr2013]

Hi All,

I am a structural guy lurking to the mechanical side in search of some assistance. I have done a search but can't quite seem to find anything.

I am managing a design project for a industrial facility which include a few atmospheric storage vessels of Class IIIB fluids. The site safety personnel is asking for some type of code that specifies how many access/egress points (i.e. platform to adjacent tank/ladder to grade, etc.) we need on the top of these tanks. They are accessed regularly for checking levels etc. but they are not permanently occupied. A lot of the OSHA code seems like it may not quite apply for this or I havent found the correct subsection, I've also looked through API 650 and some PIP standards.

If anyone has any help on a direction to point me I would greatly appreciate it.

 

[MJCronin]

During my 25 years specifying petro/chemical plant equipment, I have only found assorted client preferences and very few client general guidelines regarding the manhole/manway number question.... there seems to be no official API/ASME/OSHA code requirements.

The question about the correct number of access points/manways must be addressed by a competent and registered "Storage Tank Professional Engineer". There must be buy-in by the client as well as the client's maintenance department. Realize that the location and orientation of the manways must consider the expected maintenance/inspection requirements for the tank's current AND FUTURE expected contents !!!... Storage tanks are repurposed throughout their lifetimes. Realize that some tanks require large and very expensive shell "Cleanout doors" which have specific API-650 fabrication and welding requirements.

https://www.youtube.com/watch?v=9o3J-a4X_Is

You should also realize that there are roof mounted devices called "thief hatches" or sample hatches that serve to provide access to the tank contents.

Additionally, you must realize that roof manways also serve as a preferred location for mounting vacuum/pressure relief devices. The client must make up his mind about venting and pressure relief before you can establish the total manway situation for the tank.

https://www.ljtechnologies.com/sj/emergency-vents/94200-emergency-vent-and-manhole-cover/

https://news.thomasnet.com/fullstory/emergency-vent-provides-pressure-and-vacuum-relief-612000

Long ago, CHEVRON had developed a superb storage tank design guideline that was very useful. However, this was vacuumed up (or stolen) by SCRIBD and all other internet copies disabled. Tremendous moneymaker, that thief SCRIBD .........................

https://www.scribd.com/doc/54680702/Storage-Tanks

(Amazing how SCRIBD wants to make money off of the STOLEN information developed by others, isn't it ???)

Some things (as I remember) that seem common among the various major Petrochemical guidelines:

1) Minimum number of tank manways - two - one on shell, one on roof - Roof manway may be hinged square or circular with locking device

2) Minimum shell bolted manway size, 24" NPS (but 30" best)- Centerline approx 48 inches above grade - Consider lifting davit for blank

3) Roof mounted manway is required for tank interior coating and cleaning activities - Contact a cleaning contractor for his requirements

4) Another discussion you may find helpful:

https://www.ast-forum.com/ast_forum_tree.asp?master=12827

Please keep us in the thread and share your final decision and your basis for doing so ...

--- Anybody else out there that can contribute to this important topic ????

(More Tank Fun: .....

https://www.eng-tips.com/viewthread.cfm?qid=450551)

Regards

MJC



MJCronin
Sr. Process Engineer

 

[LittleInch]

What do you mean by access/ egress points?

Into the tank or from the tank roof?

A drawing or sketch would help.

I doubt there is any code for this sort of thing as it's too specific to the fluid, the hazard and the location.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LSUengr2013]

A drawing or sketch would help.

I just tried uploading a model view, but it seems that my computer won't let me. Probably some IT block. But it is four 14 ft. diameter tanks all in a single row, approximately 40' tall.

Current configuration has platforms connecting each one, with a spiral staircase at the second and last tank for egress. The question arose as to whether or not that was enough egress from the top of the tanks to satisfy various codes. The site likes to try to have two points of access/egress for an individual when they can. So this is driving the conversation as to if we need to add a ladder on the first tank to give an extra means of egress.

 

[mk3223]

May refer to the NFPA(30?) standard and/or the Owner's design spec for the requirement of the access or egress for tanks.

 

[MJCronin]

Class IIIB liquid .... Four 14 foot diameter tanks approx 40 foot tall ?

I would require a flat roof with a 360 degree handrail

One shell manway (30" diameter) and one roof manway (24" diameter) required per tank ....

If you need access to the inside of the tank, consider an 8" sample/thief hatch

http://jayco.org/products-category/jayco-thief-hatch/

Develop a composite sketch for the tank roofs together when you calculate and establish venting requirements (API-2000)

Sounds like you already have two means of egress for all tank roofs .... a sketch would help

IMHO, any additional ladder is not required ....

MJCronin
Sr. Process Engineer