chap 6 pressure vessels

CHAPTER 6

PRESSURE VESSELS

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

• Boiler explosion on March 20, 1905 in Brockton, Massachusetts.

• 58 killed and 117 injured.• Need of legislative rules and

regulation for construction of boilers.• The first Boiler and Pressure Vessel

Code was published in 1915.• Necessary changes made and new

sections added as need arose.

History of Pressure Vessel codes


A code is a standard that has been adopted by one or more governmental bodies and has the force of law, or when it has been incorporated into a business contract.

Codes specify requirements of design, fabrication, inspection and testing of pressure vessels.

Number of national codes have been developed for pressure vessels by different countries.

In India, the code for pressure vessels is IS-2825

What is a Code?


• It is a standard that provides rules for the design, fabrication, and inspection of boilers and pressure.

• This establishes and maintains design, construction and inspection standards providing for maximum protection of life and property.

WHAT ARE ASME CODES?


• A manufacturer obtains permission to use one of the stamps through the ASME conformity assessment process.

• The manufacturer’s quality control system is reviewed by an ASME team.

• If it meets ASME requirements and the manufacturer successfully demonstrates implementation of the program, the manufacturer is accredited by ASME.

• The manufacturer then may certify the product as meeting ASME standards and apply the stamp to the product.

ASME Codes - Manufacturer


• Excessive elastic deformation including elastic instability

• Excessive plastic deformation• Brittle fracture• Stress rupture or creep deformation

(inelastic)• Plastic instability and incremental

collapse• High strain and low cycle fatigue• Stress corrosion• Corrosion fatigue

Why follow ASME codes?


• ASME Publications Catalog,• The ANSI Catalog of American

National Standards, • the US government’s OSHA General

Industry Standards, • contact a standards organization

directly. • http://www.asme.org/catalog

ASME Codes - User


http://www.asme.org/catalog

• Insurance

• Replacement

• Proper Compliance- Size specific- Jurisdiction

• Proper ASME stamps

ASME Codes – User


Nomenclature


• A heat exchanger qualifies as a UM stamped pressure vessel if:

- Design pressure < 15psig- Internal volume < 1.5 cubic ft. for 150<P<600

psig- Internal volume < 5 cubic ft. for design P upto

250 psig

Example


• A heat exchanger qualifies as a U stamped pressure vessel if:

- Design pressure > 600 psig- Internal volume > 1.5 cubic ft. for 150<P<600

psig- Internal volume > 5 cubic ft. for design P upto

250 psig

Example


Comparison of pressure vesselsItem IS-2825 ASME Code

Section VIIIBS-5500 AD-

Merkblatter

Scope •Unfired fusion welded pressure vessels•Pressure < 20 N/mm2•Do/Di < 1.5•Di > 150 mm•Water capacity > 50 litres

•Welded, riveted, forged and brazed vessels•Water capacity>120 gal•Operating pressure > 15 psi•Di>6”

• Unfired fusion welded pressure vessels•Medium and high pressure storage vessels•Excludes transportable vessels.

•Do/Di < 1.7•Vessels and vessel parts predominantly under static load.

materials •Carbon and low alloy steels, high alloy steel, Cu and Cu alloys, Al and alloys

•Same as IS-2825•Cast iron, lined material cast iron, ferritic steel

•Carbon, ferritic alloy(low and high) .

All metallic materials and graphite, glass.

What is a Code?


Item IS-2825 ASME Code Section VIII

BS-5500 AD-Merkblatter

Design pressure

Maximum working pressure including static head + 5% maximum working pressure.

Maximum pressure at most severe conditions

Maximum pressure at most severe conditions

Based on permissible service pressure

Design tempera-ture

Highest metal temperature expected under operating conditions

Actual metal temperature expected under operating conditions

Actual metal temperature expected under operating conditions + margin for uncertainties

Highest wall temperature expected under working conditions

Comparison of pressure vessels


National code U.T.S Yield strength Sr(rupture stress)

Creep stress

ASME: VIIIDiv: 1

4 1.6 - 1

ASME: VIIIDiv-2

3 1.5 - -

BS-1515 4 - - -

BS-1515Part II

2.5 1.5 1.5 1

BS-5500 2.35 1.5 1.3 1

ANCC - 1.5 1.5 -

IS-2825 3 1.5 1.5 1

Comparison of pressure vessels


Explosions


• In spite of some of the most rigorous, well-conceived safety rules and procedures ever put together, boiler and pressure vessel accidents continue to occur.

• In 1980, for example, the National Board of Boiler and Pressure Vessel Inspectors reported:

- 1972 boiler and pressure vessel accidents, 108 injuries and 22 deaths.

• The pressure vessel explosions are of course rare nowadays and are often caused by incorrect operation or poorly monitored corrosion.


• Safety in boiler and pressure vessels can be achieved by:

Proper design and construction

Proper maintenance and inspection

Proper operator performance and

vessel operation


Stress element

Stresses in Pressurized Cylinders Cylindrical pressure vessels, hydraulic cylinders, shafts with components mounted on (gears, pulleys, and bearings), gun barrels, pipes carrying fluids at high pressure,….. develop tangential, longitudinal, and radial stresses.

Wall thickness

t

Radial stress

r

Longitudinal stressl

(closed ends)

A pressurized cylinder is considered a thin-walled vessel if the wall thickness is less than one-twentieth of the radius.

< 1/20tr

Thin-walled pressure vessel

Tangential stress θ

Hoop stress


Stresses in a Thin-Walled Pressurized Cylinders

In a thin-walled pressurized cylinder the radial stress is much smaller than the tangential stress and can be neglected.

Longitudinal stress, l

(l) /4 [ (do)2 – (di)

2] = ( p ) /4 (di)2

Internal pressure, p

Fy = 0

Longitudinal stress

(l) [ (di + 2t)2 – (di)2] = ( p ) (di)

2

4t2 is very small,

(l) (4di t) = ( p ) (di)2

l = p di

2 tl =

p (di + t)4 t

Max. longitudinal stress

Pressure area


Stresses in a Thin-Walled Pressurized Cylinders

Projected area

Hoop stress

θ

Tangential (hoop) stress

2(θ) t (length) = ( p ) (di) (length)

Fx = 0

θ = p di 2 t

Max. Hoop stress

l = ½ θ


Stresses in a Thick-Walled Pressurized CylindersIn case of thick-walled pressurized cylinders, the radial stress, r , cannot be neglected.

Assumption – longitudinal elongation is constant around the plane of cross section, there is very little warping of

the cross section, εl = constant

dr

θ θ

r + dr

r

2(θ)(dr)(l) + r (2rl) – (r + dr) [2(r + dr)l] = 0

l = length of cylinder

F = 0

(dr) (dr) is very small compared to

other terms ≈ 0

θ – r – r dr

dr= 0 (1)


chap 6 pressure vessels

Engineering

mechanical lj polytechnic

pressure vessels missam

design pressure

asme codes user missam

nomenclature missam

asme requirements

psig example missam

testing of pressure