4 replies to this topic

[abhilashpkurian]

Need Urgent help

Hello Everyone,

Our company is supposed to design an atmospheric tank with capacity of 5000 Litres which would be used for storing chemicals and then these chemicals would be injected to pipelines. The design pressure of the tank given by the client is 2kPa (g). The design asks for cylindrical horizontal tank. My query are as mentioned below.

1. Which code to follow.
2. While designing tanks, the design pressure to be considered should be gauge pressure or absolute pressure.

I am pretty sure that ASME Sec VIII would not be applicable, neither API 650, 620 or 12F. There are certain BS Codes, but I am not sure which one.

An early reply by any designer would be appreciated.

Regards,
Abhilash Kurian

[Art Montemayor]

Abhilash:

By strict ASME interpretation, with a design pressure of 0.3 psig, you are not talking about a "pressure vessel". And for 5,000 liters (1,320 gallons) you are debating a vessel that will be approximately 5 feet diameter X 10 feet long (s/s) with saddle supports. This is a very simple, relatively small vessel that should be built locally according to local UAE codes. Your fabrication shops should be well aware of what those are, in case you don't.

Your problem (or the fab shop's) will be trying to stick to the very low design pressure. I would recommend that these type of small vessels be built with available carbon steel plates that can be welded manually (stick weld). For this, I would use 5/16" or 3/8" steel plate and corresponding 2:1 ellipsoidal (or dished) heads. Gauge pressure is employed in the design of a pressure vessel.

To understand what I am talking about, refer to Eugene Megyesy's classical book, "Pressure Vessel Handbook". You should have a copy on your desk constantly.

[abhilashpkurian]

Dear Sir,

I am a huge fan of yours.

I require a few guidelines from you. I am having the tenth edition of "Pressure vessel handbook" by Eugene F MEgysey. The book I feel is the best for Pressure Vessel Design. My queries are as mentioned below.

1. Can the vessel indicated by be considered as a Pressure Vessel based on the design pressure that has been indicated?
2. As per the book, the design pressure should be 30 psi more than the operating pressure or 10% additional to the operating pressure, whichever is higher. Should I be taking this into consideration.
3. I was initially planning to use flat ends, instead of 2:1 ellipsoidal head. But the design showed that I should use 42 mm plate if I went for flat ends. So I decided to use 2:1 ellipsoidal head.
4. I require the dimensions of 2:1 ellipsoidal head. The crown radius, knuckle radius, skirt length etc, which are not mentioned in the book.
5. Is there any thumb rule regarding the l/d ratio? In the l/d ratio, l refers to the length of the shell including the skirt length or without it?
6. Are there any other standards that we should use..like EN 13445? or whether design as per Eugene F MEgysey is fine.
7. All the equations mentioned in Pressure Vessel Hanbook are taken from ASME Sec VIII Div. 1. Am I correct?

I would request you to reply to my queries at the earliest.

Thanks and regards,
Abhilash Kurian

[Art Montemayor]

Abhilash:

Go to:
http://www.pveng.com...?content_id=138

and download all the free information on Pressure Vessel Design Charts. Also download all the information given on how to estimate a pressure vessel design. This information is very authoritative and helpful.
also go to:

http://www.cheresources.com/invision/index.php?showtopic=1557&st=25

on Post #50, and download my free Excel workbook, “Vessel Volume”. In this workbook you will find information on heads. My comments to your queries are:

1) The legal definition of pressure vessel varies from country to country, but it often involves the maximum safe pressure that the vessel is designed for and the pressure-volume product, particularly of the gaseous part. In the United States, the rules for pressure vessels are contained in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code and in the 2004 Edition of the ASME B&PV Code, Section VIII, Div 1 the operating pressure that defines a pressure vessel is 15 psi – regardless of volume.

2) Your design pressure (2 kPag) is so small that, as I stated previously, you will surely find yourself limited by the minimum thickness of the steel plate that you can safely and efficiently weld. I predict you will wind up with a practical vessel that can easily withstand 200 kpag as the practical vessel to build efficiently and economically. You have to be practical as an engineer. Only pure scientists can afford to be impractical.

3) Ellipsoidal 2:1 heads are very practical. However, they are expensive sometimes – depending on where you are located. That is why low-pressure (10 – 50 psig) dished heads are employed in the fabrication of many low pressure tanks such as yours. I would recommend you try to employ a dished head – but certainly not a flat head. Read and study my workbook.

4) for details on ellipsoidal and dished heads always refer to the manufactuer’s literature and information. Usually the straight flange on such heads is approximately 3 inches. Again, refer to my workbook.

5) The “rule of thumb” I always use for determining or fixing the L/D ratio is: use the most cost effective steel plate size combined with the job scope requirements on footprint and space available. You will find that the fabricator has a large input on determining the cost effective steel plate size that will yield the best vessel dimension – if you approve it.

6) ALWAYS design to the specific, local pressure vessel codes – in accordance with your industrial insurance coverage. Your industrial insurance company should play a strong part (together with the pressure vessel regulations in the UAE) in fixing the allowable design code that you can employ. Do not forget that as professional engineers we are always accountable to the public’s safety and welfare and, as such, we have to abide by legal regulations where we practice our engineering.

7) Not ALL the equations in the Megyesy book are from the ASME Code. Most, I would suspect, are.

[mdteng]

Abhilash:
As Art said, you can design the vessel according ASME VIII, Div1 regardless of the design pressure.

Section U-1©(2) of the code states: "Based on the Committee’s consideration, the following classes of vessels are not included in the scope of this Division; however, any pressure vessel which meets all the applicable requirements of this Division may be stamped with the Code U Symbol"
And one of the clauses is:
"(h) vessels having an internal or external
operating pressure not exceeding 15 psi
(100 kPa) with no limitation on size [see UG-28(f)]"

I think that this is your case. Surely, the minimum thickness of your vessel will be deternined by the supporting condition and not for the internal pressure.

Besides; are there any process restriction about design this vessel in Fiber reinforced Plastic?
ASME B&PV code has the Section X "Fiber Reinforced plastic pressure vessels". In this section, Class II vessels fits your pressure requirements, both design methos can be applied A or B.

Also I was reading the AWWA D120 - 2002 "Thermosetting Fiberglass-Reinforced plastic tanks". Is applicability limit is 15 psi

The other standard that covers FRP Vessels is BS 4994

Regards
Martin