8 replies to this topic

[abhilashpkurian]

Dear All,

We are fabricating few rectangular atmospheric tanks for a client. The design is as per Roark's and Young Formula, and also Pressure Vessel Handbook by Eugene F Megysey. The client requires a manhole of 24" (basically 600mm OD) for all the tanks. The tank capacities and their dimensions are mentioned below.

1. Tank 1
Working capacity: 0.5 cu. m
Outside Dimensions: 0.9m x 1.0 m x 0.9 m

2.Tank 2
Working capacity: 7.6 cu. m
Outside Dimensions: 2.1m x 3.9m x 1.1m

3.Tank 3
Working capacity: 4.05 cu. m
Outside Dimensions: 1.8m x 2.7m x 1.0m

4.Tank 4
Working capacity: 2.8 cu. m
Outside Dimensions: 1.6m x 2.0m x 1.1m

5.Tank 5
Working capacity: 1.0 cu. m
Outside Dimensions: 1.0m x 1.6m x 0.9m


My queries are as mentioned below.

1. For tank 1, the manhole diameter as requested is quite large. We propose to go for OD 500mm. This is because of space restriction on the top of the tank. There are other nozzles coming on the top of the tank. Is there any thumb rule for deciding on the size of the manhole. Is there any reference that we can provide to the client to have this deviation (to change the size of the manhole size from OD 600mm to 500mm)?

2. Are there any other design standards for the design of rectangular atmospheric tanks?

All replies are welcome.


Regards,
Abhilash Kurian

[astro]

Sounds like your client might have their head stuck in a corporate standards book and it sounds like you are trying to offer a workable compromise. I think many of us have come across this sort of narrowmindedness in our travels.

I am aware that pressure vessel standards offer guidance on the size of manways & observation nozzles. There the balance is between the need for internal inspection and the mechanical integrity issues of removing too much of the vessel thereby weakening it.

Couple of questions / points to run through with vessel entry points:

1. What will the entry be used for?
Does the client expect to put a person inside Tank 1? The safest way to inspect a vessel or tank is to do so without entering it. Given the size of the tank, entry is impractical anyway.
I would have thought 500mm would be sufficient for cleaning or internal inspection from the opening.

2. What is the risk associated (risk to tank integrity, risk of blockages and risk to personnel) with the tank contents?
You need to assess those 3 points (amongst others) when weighing up the practicalities. If the risks turn out to be low all round then you would start to have a valid basis to argue for very small or no openings in the equipment.

3. What needs to pass into the tank during internal inspection?
If internal inspection is a requirement then practically you need to provide sufficient space to allow for entry of a person, equipment and services (e.g. lighting) during that activity. You also need to consider emergency egress in the event of the need for personnel recovery. The larger the opening the easier it will be.

All the best with the debate.

[JoeWong]

On top of questions raised by Astro,

How many nozzles and what are the purpose of those nozzles ?

[Jiten_process]

one more thing further to what astro has already asked...the manhole size criteria should also get compliant with factory act 1948. Depending on the hazard and risk with regard to chemical used you have to comply factory act rule too.

We for our project supplied vessel with 450-500mm size manhole.

[abhilashpkurian]

On top of questions raised by Astro,

How many nozzles and what are the purpose of those nozzles ?

Sir,

Please note that there are seven nos of 2" NB nozzles on the top. Considering the flanges (150#) of the 2" nozzle, it is nearly impossible to accomodate a 600 NB hole. Any sugggestions?

Regards,
Abhilash Kurian

[JoeWong]

Abhilash,

You have not mentioned the function of the nozzle. Anyway...

Per previous experience, not all nozzles need to come in from the tank top; they may come in from side wall. Please evaluate the function of the nozzle and advise your client to move them to the side wall.

[djack77494]

If you truly want a manway, meaning you want a man to be able to enter the vessel, then I'd want at least a 24 inch or 600 mm opening. Anything less is too small in my opinion and in the standards of many companies. This is notwithstanding the fact that there are people who can enter smaller openings - you don't really want a opening just large enough for entry and egress; it needs to be bigger for a variety of reasons. With a small vessel where a properly sized manway would be a significant part of the vessel's diameter, you may get to the point where it is more practical to install vessel flanges; essentially cut the vessel in half and connect the two halves with a set of flanges. This could well be your best choice if the vessel diameter is not too large (say to 1 m), but at large size will become unattractive. But a large vessel will be able to accomodate a 24" manway, so I think there should be no problem.

[Qalander (Chem)]

If you truly want a manway, meaning you want a man to be able to enter the vessel, then I'd want at least a 24 inch or 600 mm opening. Anything less is too small in my opinion and in the standards of many companies. This is notwithstanding the fact that there are people who can enter smaller openings - you don't really want a opening just large enough for entry and egress; it needs to be bigger for a variety of reasons. With a small vessel where a properly sized manway would be a significant part of the vessel's diameter, you may get to the point where it is more practical to install vessel flanges; essentially cut the vessel in half and connect the two halves with a set of flanges. This could well be your best choice if the vessel diameter is not too large (say to 1 m), but at large size will become unattractive. But a large vessel will be able to accomodate a 24" manway, so I think there should be no problem.

This 24"or 600mm is exactly in line with most recent OSHA recommendations on the issue,I believe.

Additionally for safe and secure postures without hurting/iternally injurring one's muscele's and/or ligaments etc. it is better indeed.

[abhilashpkurian]

The client (Shell) agreed for 500 mm opening for the Man hole.
Thanks everybody for their views.