Design : 2 : Shell (External Pressure)

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External pressure can be due to internal negative Pressure, or external loading like wind, earthquake etc. or live load, snow load etc.

One can design Pressure vessel for either sever combination of various load or for most possible occurrence of load combination.

Load combinations are given in respective ‘Building Code’ like API, UBC, IS etc.

Yes, If you noticed I’ve said ‘Building Code’, why? as most of these loading decides how the pressure vessel, and if it fails, it can harm the occupants. hence design of such loading will be governed by building codes.

These Building code will give su way to calculate loading on tank/vessel, and then our design code like ASME, BS,EN will tell us how to derive the thickness from them.

one should note that, nearly all the design code talks about +ve Internal pressure & -Ve internal pressure & its design rules, but none of the code talk about how to do thickness calculation for the loads specified above.

In latest edition of ASME it does talk about these loading, and ask user to use Engineering practices to calculate loadings (UG-22), loading listed in this sections are
(a) internal or external design pressure (as defined in UG-21);
(b) weight of the vessel and normal contents under operating or test conditions;
(c) superimposed static reactions from weight of attached equipment, such as motors, machinery, other vessels, piping, linings, and insulation;
(d) the attachment of:
(1) internals (see Appendix D);
(2) vessel supports, such as lugs, rings, skirts, saddles, and legs (see Appendix G);
(e) cyclic and dynamic reactions due to pressure or thermal variations, or from equipment mounted on a vessel, and mechanical loadings;
(f) wind, snow, and seismic reactions, where required;
(g) impact reactions such as those due to fluid shock;
(h) temperature gradients and differential thermal expansion;
(i) abnormal pressures, such as those caused by deflagration;
(j) test pressure and coincident static head acting during the test (see UG-99).

In next section, we will discuss how to calculate final thickness of a vessel considering all loadings

Design : 1 : Shell

Technical,

We design pressure vessel for longitudinan and circumferencial stresses. Now whats that?
Ok, longitudinal stresses comes on circumferencial joints, where as circumferencial stresses comes on longitudinal joints.
And to add cherry on top circumferencial stresses are twise that of longitudinal stresses.
If you are not yet twisted your tongue, and to avoid that we generally call them c’seam and l’seam and c’stress and l’stress.

In below pictures, one can identify types of Seams and Stress.

here p is design pressure, R is internal Radius, L is Length of shell, t is thickness of shell.

Hence with the basic mechanical formula,
t for Hoop stresses = pL (2R)/2 xStressx L = pR/Allw. Stress
t Longitudinal stresses = px3.14xR^2 / (2×3.14xRxAllw. Stress) = PR/2 Allw. Stress

& what ASME Says..
t for Hoop Stress = PR/(SE – 0.6P)
Where S > All. Stress, E > Joint Eff. or factor of safety
why 0.6 P, because, its factor of safety set by ASME People

&
t for Longitudinal Stress = PR/(2SE+0.4P)

Note the ‘2’ in denominator..

if E remain the same for both cases, then thickness given by Hoop stress will be twice that of by Longitudinal stresses


For Calculation Sheet Visit http://sumitmechsoftware.blogspot.com/

Pressure Vessel catagory (Design Persay)

Technical,

OK..

The Billion dollar Question…

Just to make it easy, we will break the pressure vessel in two category..
1. Pressure Vessel without external loading &
2. Pressure Vessel With external Loading

For Category 1, we can use ASME Section VIII Div. 1 directly, where as for Category 2, we need to consider additional loadings. And for additional loading we need to follow the basic engineering practices.

Hence, in future section, 1st we will discuss the Sizing of Pressure vessel as per ASME Section VIII Div. 1, and then we discuss the additional loading part.

“Terms” in Pressure Vessels

Technical,

Failure: Failure of a structure is an event, the transition from a normal working state, where the structure meets its intended requirements, to a failed state, where it does not meet its requirements
Limit states: A limit state is a structural condition beyond which the design performance requirements of a component are not satisfied. Limit states are classified into ultimate limit states and serviceability limit states
Elastic limit states: An elastic limit state is a structural condition associated with the onset of plastic deformation. This term is usually used in connection with monotonic actions, and it relates to virtual structures, usually with zero initial stress distribution
OPERATING PRESSURE : The pressure which is required for the process, served by the vessel, at which the vessel is normally operated.
DESIGN PRESSURE : The pressure used in the design of a vessel. It is recommended to design a vessel and its parts for a higher pressure than the operating pressure. A design pressure higher than the operating pressure with 30 psi or 10 percent, whichever is the greater, will satisfy this requirement, The pressure of the fluid and other contents of the vessel should also be taken into consideration.
MAXIMUM ALLOWABLE WORKING PRESSURE : The internal pressure at which the weakest element of the vessel is loaded to the ultimate permissible point
HYDROSTATIC TEST PRESSURE : One and one-half times the maximum allowable working pressure or the design pressure to be marked on the vessel when calculations are not made to determine the maximum allowable working pressure.

There are many more terms than this… but to start with.. these are sufficient.

What is Pressure Vessel?

5 CommentsTechnical,

Pressure vessels are probably the most widespread “machines” within the different industrial sectors. In fact, there is no factory without pressure vessels, steam boilers, tanks, autoclaves, collectors, heat exchangers, pipes, etc.
More specifically, pressure vessels represent components in sectors of enormous industrial importance, such as the nuclear, oil, petrochemical, and chemical sectors.
There are numerous Codes & Laws present in each country to control the usage of this ‘machines’! its useful but its dangerous!
What one need to design a Pressure Vessel?
● good workmanship with regard to the tools used,
● knowledge of the basic engineering principles and the phenomena involved,
● fantasy and creativity with regard to the selection of the models used,
● fair knowledge of the legal requirements pertaining to design,
● fair knowledge of manufacturing and testing procedures, and especially
● extreme carefulness in each step, from the design specification to the design
report.

Pressure Vessel mostly are made-up of ‘Steel’ Steel behaves in an elastic fashion even beyond the proportional limit, as long as another characteristic point corresponding to stress called elastic limit is not exceeded.In practice, we typically equate the proportional limit to the elastic limit.

we always discuss the steel’s behavior at room temperature. It is, however, of the greatest importance to be aware of the influence of temperature on the mechanical characteristics of the material. As we shall see, not only temperature but also time may have a strong influence.

Next we will discuss some “TERMS”

What Next?

Technical, Uncategorized

Now, let us start new topic, on design of pressure vessel!

I think this one of the interesting subject, and we find lots of data over here and their defining how to design pressure vessel.

Some people take advantage of this and confuse you some time.. end result you may get over size vessel (high cost) or under size vessel (Dangerous!)

Solution.. buy High end software!! Sure. thats the last thing I’ll recommend!

Hence onward, for few more post we will discuss this subject, and I’m open for suggestions and lengthy discussions over this 🙂

So next post.. Over view on Pressure Vessel (Simplified 🙂

Visit to Drinktec

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Hello All from Munich!
Right now I’m at drinktec,and sharing my experience with you all.
Drinktec (website : www.drinktec.com) Drinktec is an exhibition which happen at Munich germany after each 4 year! Its for people from Brewery & Beverages.

The exhibitors are manufacturers & supplier from/ for same Industry.
Its a good experience for new bee like me, who is very new to this industry. you will find here huge stalls from all equipments around the world. I’ve seen huge bottling plant made alive in Stall at exhibition.

I’ll share few pictures from exhibitions soon.

Chao!

Material Properties

Technical,

The differences have to be taken into consideration by both designer and welder. The high thermal expansionand low thermal conductivity of the austenitic steels lead to higher shrinkage stresses in the weld thanwhen carbon and ferritic steels are used. Thin sections of austenitic steels may therefore be deformed when an abnormally high heat input is used

These steels are mainly used in wet environments. Withincreasing chromium and molybdenum contents, the steels become increasingly resistant to aggressive solutions. The higher nickel content reduces the risk of stress corrosion cracking. Austenitic steels are more or less resistant to general corrosion, crevice corrosion
and pitting, depending on the quantity of alloying elements.
Resistance to pitting and crevice corrosion is very important if the steel is to be used in chloride-containing environments. Resistance to pitting and crevice corrosion increases with increasing contents of chromium, molybdenum and nitrogen.

Material of Construction

Technical,

In pressure Part Industry we use various type of material.

Typically in industry like this, we mainly classify material as Mild Steel also known as Carbon Steel, we also use low & high alloy steel & yes stainless steel!

What diffrentiate staineless steel from Carbon steel is its corrosion resistance properties, whcih comes because of its alloy elements.

In my blog hence onward, we will discuss about the material of constrution that we use in this industry.

I’ll come back soon.