Heater Tube Thickness Caldf

7/26/2019 Heater Tube Thickness Caldf

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THICKNESS IN PETROLEUM

REFINERIES

API 530

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SCOPE

API 530 covers desi n rocedures of rocess fired

heater tubes (direct fired, heat absorbing tubes withinenclosures)

urnace u es an was e ea exc angers u es are

designed on API 530

Desi n of external i in is not covered in this

standard



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LIMITATIONS

A l to thin tubes with thickness to dia ratio less

than 0.15Apply to seamless tubes. When applied to welded

u es mu p y a owa e s ress w o n e c ency

No consideration for graphitization, carburization, or

h dro en attack



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DESIGN

design conditions: Elastic Design (lower temperature)

Rupture Design (higher temperature)

Creep rupture occurs in steel at highoperating temperature even at stress levels

well below the yield strength

Creep rupture is permanent deformation, afailure mode other than elastic/plastic



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DESIGN

When tube tem erature will be hi h enou h for cree

to be significant, tube will fail from creep rupture For steels operating at lower temperature, the effects

o creep w e neg g e e as c

Experience indicates that in elastic case tube will last

indefinitel unless a corrosion or oxidation

mechanism is active



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DESIGN

Elastic design Based on preventing bursting

Design in elastic range at lower temperature

Allowable stresses based on yield strength

ee

oes

PS

DPt

+

=

2

CAtt sm +=

w ere,

Pe = design pressure

Se = allowable stress in elastic range

o

ts = stress thickness

tm = minimum thickness

CA = corrosion allowance



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DESIGN

Rupture design Based on preventing creep rupture

Design in creep range at higher temperature

Allowable stresses based on rupture strength

rr

or

s PS

DP

t +=

2 fCAtt sm +=

where,

Pr = rupture design pressure

r

f = corrosion fraction function of B and n

B = CA/ts

n = ru ture ex onent at desi n metal tem erature



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DESIGN

Known values will be design pressure, design metal

temperature and outside diameter of tubes Determination of design criteria (elastic or rupture)

The same graph will provide the value of allowable

elastic or rupture strength ere, we w go t roug ot o es gns



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DESIGN

We take the exam le of a coil

Design pressure = 38 kg/cm2

Design temperature = 660 C

ater a o co -

Graph will define the type of design to be followed



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DESIGN

Ru ture desi n overns as allowable stress is

less than elastic marginal stress More data is required to get the value of

allowable rupture strength like design life of

tube (to be decided by the designer) and

design pressure

See the ra h on the next a e for clarit



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DESIGN

So allowable ru ture stren th comes out close to 41

MPa considering design life of 100,000 hrs Likewise, we can evaluate the thickness by using the

ormu as g ven a ove rup ure pressure s e ne

Elastic design is simple to practice design procedures



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Heater Tube Thickness Caldf

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