ASME VIII

SUBSECTION A GENERAL REQUIREMENTS

(UG)

Prepared by: Eng. Mahmoud Elsayed E-mail: Onemahmoud_1988@yahoo.com

Contents Materials Pressure parts Non pressure parts Forging materials Casting materials Pipes and tubes Bolts Welding materials Design Shell design under internal pressure under external pressure Head design

Materials Materials for pressure parts like shell and heads shall conform

specifications in ASME SEC II D

Materials for non pressure parts like skirts,lugs,supports, fins,……. etc need not need not conform to the specifications for the material to which they are attached or to material specification permitted in this Division.

materials covered by specifications in section II is not restricted

by production method unless so stated in the specifications and as long as it complies with specs requirements

Materials Materials other than those allowed by this Division

may not be used, unless data thereon are submitted to and approved by the BPVC Committee in accordance with Appendix 5 in Section II, Part D.

Materials outside the limits of size and/or thickness

given in the title or scope clause of the specifications given in Section II, and permitted by the applicable part of Subsection C, may be used if the material is in compliance with the other requirements of the specification,1 and no size or thickness limitation is given in the stress tables.

Materials

Materials other than allowed by this division shall not be used unless it is approved from BPV committee

Materials outside the limits of size and thickness mentioned in ASME II and permitted by subsection C may be used if materials comply with other specs requirements and no thickness limitation given in stress tables

Materials

Forging materials may be used in pressure vessel construction provided that the material has been worked sufficiently.

Casting materials may be used in construction of pressure vessels. material allowable stress should be calculated as per UG 23 multiplied by casting factor from UG 24

Materials

Pipes and tubes of seamless or welded shall be used for shells and other pressure parts of pressure parts , max allowable stress for such shall be determined according to UG 23

Materials

Tubes after finning should be tempered Max allowable stress should be calculated as per UG 23 MAWP shall be determined based on the root thickness of finned

thickness or the thickness of unfined section which ever results in lower MAWP

In addition to the above and specs requirements as per sec II finned tubes shall be subjected to pneumatics and hydrostatic test as per the following requirements

Finned tubes may be used as shell of pressure vessels or other pressure parts in case of :

Pneumatic test of not less than 1.7 MPA for %sec without evidence of leakage

Hydrostatic tests according to UG 99

Materials

Welding materials used for production should comply with ASME II C and ASME IX requirements

Materials Bolts and studs may be used for the attachment of removable

parts. Specifications, and maximum allowable stress values for acceptable bolting materials are given in the tables referenced in UG-23.

Studs shall be threaded full length or shall be machined down to the root diameter of the thread in the unthreaded portion, provided that the threaded portions are at least 11⁄2 diameters in length.

DESIGN

Before introducing the design equations and procedure we should define first some main parameters that used in design, this parameters can be summarized as follows:

Design temperature Design pressure Loading Maximum allowable stress of material

Design temperature When we say design temperature we should consider

two values of temperatures Maximum temperature that is because higher temperature affect on the

strength of material the higher the temperature the lower the strength

Minimum temperature that is because low temperature negatively affect on

the toughness of the material

Design temperature

Maximum temperature •The maximum temperature used in design shall be not less than the mean metal temperature (through the thickness) under operating conditions

•If it necessary mean metal temperature may be determined through computation or measurement from equipment under equivalent conditions in service

•Design temperatures that exceed the temperature limit in ASME SEC II are not permitted

•design temperatures for vessels under external pressure shall not exceed the maximum temperatures given on the external pressure charts

Design temperature

Minimum temperature •The minimum temperature used in design shall be the lowest expected temperature during service, taking in consideration lowest operating temperature, operational upsets, auto refrigeration, atmospheric temperature, and any other sources of cooling

•MDMT corresponds to MAWP should be mentioned on the vessel Nameplate

•Impact test requirements should be as per UCS 66

Design pressure

Design pressure shall meet the most severe pressure that the vessel will be subjected to while being in service.

Loading Different loadings should be considered through the design of pressure

vessels like : internal or external design pressure weight of the vessel reactions from weight of attached equipment, such as motors,

machinery………… the attachment of: (1) internals (2) vessel supports, such as lugs, rings, skirts, saddles, cyclic and dynamic reactions due to pressure or thermal variations wind, snow, and seismic reactions impact reactions such as those due to fluid shock temperature gradients abnormal pressures test pressure

Maximum allowable stress (UG 23)

The maximum allowable stress value is the maximum unit stress permitted in a given material used in a vessel constructed under these rules. The maximum allowable tensile stress values permitted for different materials are given in ASME Section II, Part D.

Part Application UCS 23 Carbon steel UHA 23 High alloy steel UCI 23 Cast iron UHT 23 Heat treated ferritic steel

Design

The wall thickness of a vessel computed by these rules shall be determined such that, for any combination of loadings listed in UG-22 that induce primary stress and are expected to occur simultaneously during normal operation of the vessel, the induced maximum general primary membrane stress does not exceed the maximum allowable stress value in tension

Design

Before introducing the formulas that govern design of pressure vessel , we should talk a look of pressure vessels parts which are designed

Design Pressure vessel mainly consists of: 1. Shell 2. Heads 3. Nozzles 4. Supports(saddles,skirts,lugs) For each of the previous we will introduce the governing equations for design

according to ASME VIII DIV 1

2-Shell design

1-Shell Shell of pressure vessel is designed based on the pressure that it is subjected to either internal or pressure Shell design can be classified according to ASME VIII into two categories.

1-Shell subjected to internal pressure

2-Shell subjected to external pressure

1-Shell

a-Shell subjected to internal pressure

1-Shell Under internal pressure

Under internal pressure For the vessels subjected to internal pressure

thickness should be the greater thickness from the following equations.

1-Shell Under internal pressure

P internal design pressure R vessel inside radius S allowable stress of material

E Joint efficiency (UW 12) t Minimum required thickness of shell

1-Shell

b-Shell subjected to external pressure

1-Shell Under external pressure

Criteria of designing vessels under external pressure is slightly different from the criteria used in internal pressure design.

the next section we will introduce the procedure according to ASME VIII but before introducing it some parameters should be defined first

1-Shell Under external pressure

P external design pressure

Ro Vessel outside radius

Do Vessel outside diameter

E Joint efficiency (UW 12)

A,B Factors determined from ASME SEC II

t Minimum required thickness of shell

L Design length

1-Shell Under external pressure

Designed length is determined according to the following figure which depends on the geometry of the vessel

D/t 10 Inputs D,P,L Assume t

Calc L/D,D/t

Get value A (ASME II D)

Enter material charts in ASME II to get value B

Pa>P

start

finish

yes

No

No

Yes

Next slide

D/t >4

Get value A (ASME II D)

Enter material charts in ASME II to get value B

finish

yes

No

Pa=min(Pa1,Pa2)

Pa>P yes No Repeat all steps from

assuming t

1-Shell stiffening ring

For stiffening rings attachment, the minimum moment of inertia of the ring should not be less than the calculated from the following equations.

1-Shell stiffening ring

Is moment of inertia of ring about its neutral axis which is parallel to the axis of shell

Is’ moment of inertia for ring and shell As cross section area of ring A factor determined from ASME SEC II B factor determined from ASME SEC II Ls ½ distance from RING CL to next line of

support +1/2 distance from ring to other line of support

2- Head design

2-head

For Ellipsoidal heads

The minimum required thickness for head can be calculated from the following formula:

2-head

For torispherical heads

The minimum required thickness for head can be calculated from the following formula:

2-head

For hemispherical heads

The minimum required thickness for head can be calculated from the following formula:

2-head

For conical heads

The minimum required thickness for head can be calculated from the following formula: