Cleanouts are mandatory according to api 650? 2

[jrafael95]

Hello, that's my doubt:

Just a hypothetical scenario...

If i have a small Diesel tank built according to API 650 (like 6m dia and 6m height),and a 500mm manhole on the shell, can I use the manhole to clean the tank?

Do I really need a cleanout door to clean the tank or can i use the manhole for cleaning purposes?

I just read this post (

https://www.ast-forum.com/ast_forum_tree.asp?master=7763)

and got curious

Where to look for the answer to such a question?

 

[IFRs]

API 650 does not require you to have any penetrations in the tank shell but if you do put some in, it gives you the minimum requirements for them. In that spirit, cleanouts or manways are not required but if you choose to put one or the other or both in, API 650 shows you how. How you use your manway(s) is up to you. Flush cleanouts are typically installed when you expect a lot of BS&W or when the stored product is hard to get out, ie asphalt, wax, heavy waxy sandy crude, etc or when for some reason sweeping the residue out a flush cleanout is your best option. Diesel is pretty easy to suck dry, wash and clean. A flush cleanout might make that job easier but most diesel tanks don't have them that I know of. The downside to a flush cleanout is you should have a concrete or otherwise leak proof basin outside the tank at the cleanout to accept the material swept into it and be safely and cleanly collected and disposed of. Other downsides are high initial cost and additional cost and complexity when replacing the bottom or installing a secondary bottom in the future.

Incidentally, I don't think that conversation on AST Forum ever properly answered the question. I think the correct answer is that flush cleanout doors are not required to be part of the PWHT assembly. Only the parts specified in 5.7.4.1 need be assembled and PWHT.

 

[HTURKAK]

SOME ADDITIONAL INFO to IFR 's post;

1- You may choose 500mm manhole and that dia. confroms API 650 req.s however, some companies having jurisdiction specify min.600 mm for manhole size.. You are free to use for cleaning purposes ..

2- You DO NOT NEED cleanout door .. Moreover , some companies does not allow the use of clean outdoor for ( gasoline, diesel ..etc). . Rgarding the bottom slope, the typical bottom arrangement is, cone down to facilitate complete emptying of the storage tanks.

 

[jrafael95]

Dear @IFRs and @HTURKAK, thank you both for answering my question.

I'm kinda new in this industry and learn so much with you and this forum.

Greetings

 

[IFRs]

Notes (mostly just my opinions, and therefore suspect):

Per API 650 5.4.4 bottom slope is cone up unless otherwise specified by the owner.

Cone up has the advantage of not stressing the shell when the interior of the tank settles relative to the area under the shell (not that uncommon), but water (and therefore corrosion) settles at the corner weld.

Cone down has the advantage of a single point where liquid wants to drain, but it is harder to pump out BS&W because it is further away, stresses the shell if the interior foundation settles, interferes with a center column and corrosion from water is in a less visible and detectable area.

Shovel bottom drains better than cone up, some foundation and tank contractors are unfamiliar with this configuration, it is better for drain-dry type, can result in less dead inventory and tank cleaning by washing and sweeping to a flush cleanout is easier.

Drain-dry bottoms can be better for emissions.

In my opinion, a 20" [500mm] shell manway should be outlawed - it is too small for easily working through and is quite poor for safe egress, 24" [600mm] is passable but still tight for a worker with SCBA, 30" [900mm] is much better, and 36" [1050mm] is a pleasant luxury for those who have to work inside.

 

[MJCronin]

Just my two cents ....

FIRST: Agreed that diesel fuel is very clean and that extensive cleaning of the tank internals should be rare .....

A cleanout door on a DIESEL FUEL tank is way overkill ..... however, I have frequently seen tanks become "repurposed" by the plant staff and the cleaning requirements of a repurposed tank should be kept in mind. See if you can get the client to make up his mind on this issue..

SECOND: Consider a low cost Ventilation Roof hatch in addition to a shell manway.... Talk with the contractors who perform internal tank inspections and find out what they prefer. A roof hatch to clear the internal atmosphere quickly can save money, time and make the operation safer..... Of course, having a roof hatch means that your new tank must have access to the roof...

THIRD: I certainly agree with the experience and knowledge of IFRs as noted above regarding larger manways. In my opinion, the 30 an 36 inch manway coverplates can become difficult to handle and tank davits (or similar means) should be considered for safety reasons ...

Please keep us in the loop and let us know what are your final design decisions..

Best Regards

-MJC

MJCronin
Sr. Process Engineer

 

[HTURKAK]

Cone down bottoms typically preferred for refined products which are lighter than water (in this case diesel ). They have some advantages such as;
- the tank can be drained completely, so better for the tanks with frequent product changes .
- the contact with water minimized..

I also agree that , it has some disadvantages.


The subject tank has 6m dia and 6m height . The roof for that dia. should be self supported cone roof. Nowadays, alu. dome roofs widely preferred for product tanks without any interior column.

These are my personnel opinions.

Kind regards..

 

[dik]

out of ignorance, by cone up or down, do you refer to the bottom being slightly concave? or convex? inquisitive mimes want to know. Thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

Yes ..but the terms convex and concave are used for curved lines or surface. In this case the bottom plate is in the form of cone.
The following picture shows the cone down concept..

Kind Regards