03 PPP TTE VLS AND API 510

© Matthews Engineering Training Ltd

INSPECTING PRESSURE VESSELS (INCLUDING API 510)


Try this

What are the major design differences between these two

vessels ?


Vessel design

Design has an effect on:

• Where the greatest stresses are

• Which locations are most critical for defects

• Key areas for inspection


Key design issues related to inspection

1.Shell stresses2.Head/shell ‘discontinuity’ stresses3.The principles of compensation4.Shell distortions


Shell stresses

1


2 basic sets of assumptions:

Thick shell assumptions(mainly headers)

Thin shell assumptions (just about everything else)

Membrane theory (easy)

Lame equations(more complex)


So,membrane theory is the main one of relevance for inspectors

This assumes that

a vessel shell is

2-dimensional


Shell welds

Which weld is the most critical and why?

Longitudinal

Circumferential


Shell stresses

This is why longitudinal welds are type ‘A’ in ASME V111


The evidence


Head-to-shell stresses

2


The head/shell joint

P

How is the shell

trying to deform?

What effect is the

head having


The result is:

HERE


What affects the size of the head/shell

discontinuity stress?


Discontinuity stresses

Types of head:Ellipsoidal,Torispheroidal

Note the a:b ratio

What is this for?


How far down the shell do the discontinuity stresses

extend?

?


3Compensation


Compensation is needed because vessels have openings

The opening reduces the

strength of the shell

By how much?10%?20%?


So, compensation needs to be added to restore the shell

strength


2 different types of compensation

Use a thicker nozzle

and/or a thicker shell

Use a compensation pad

on the shell


Method

© Matthews Engineering Training LtdImportant area

Pad-type


Example:Pad type

Note small width of pad


What type is this?


Which type?


What about this one?


The effect of nozzle diameter ?

d<D/3 d>D/3


From an inspection viewpoint:

Defects on welds on ‘large nozzles’are more ‘significant’


Examples

Self-reinforcing nozzle :large diameter


This one?


44

Shell distortions


Out of roundness

OOR produces large

increases in

membrane stresses owing to bending

Typical limits


OOR example

What would you conclude about this vessel ?


Vessel codes have tight limits on other types of shell

distortions


Other design Other design limitslimits


Basic vessel design:Summary

• Why is a little bit of design knowledge important in inspection?

• Where are the highest stress levels likely to be in a pressure vessel?

• Which are generally the ‘most critical’ welds


API 510

PRESSURE VESSEL

INSPECTION CODE


THE PURPOSE OF THE STANDARD IS, BASICALLY:

To fit in with the philosophy of ASME 1 and V111 For activities relating to:

Maintenance inspection Repair Alteration

and re-rating

API 510


THE US-BASED ‘FAMILIES’ OF CODESComponents

Storage Tanks

Power Boilers

Unfired Vessels

Piping Systems

Valves Pressure Relief Valves

Construction codes (i.e. manufacture only)

API 620 API 1650

ASME 1 ASME VIII-1

ASME B31-1ASME B31.3

ASME 16.34API 600-609

ASME 1ASME VIIIAPI 2000‘In-

service’ codes (covering inspection, repair, and re-rating)

API 653

-

API 510

API 570

API 598API RP 591

API RP 576

‘Support’ technical documents

API 651API 652API RP 575

ASME RP-573ASME II, V, VI, IX

ASME B16.5API RP 572ASME II, V, IX

ASME II, V, IXAPI RP 574

API RP 574ASME V, X

ASME PRC 25API 527ASME V, IX API RP 579 ‘Fitness for service’

API Guides for Inspection of Refinery Equipment (IRE)


SO, MUCH OF THE CONTENT OF API 510 IS DIRECTLY RELEVANT TO:

ASME vessels

(and the specific way that they are designed ,

manufactured and certified By the AI),BUT IT CAN BE USED FOR OTHER

VESSELS ALSO

API 510


THE SCOPE OF API 510

Vol>0.141 m3 and P>250 psig

Vol>0.042 m3 and P>600psig

P=design pressure (not working pressure)

API 510


CORROSION AND MINIMUM THICKNESS EVALUATION

API 510 concentrates on

assessing corrosion in regions of circumferential

stresses

WHERE ARE THESE AREAS IN A VESSEL

API 510


WHAT ABOUT REAL VESSELS WITH NOZZLES?

API 510


AREAS WITH NOZZLE OPENINGS

The averaging must be done within

the reinforcement limits

API 510


‘WIDELY SCATTERED PITS’ CAN BE IGNORED AS LONG AS :

20 cm DIA

2)Total pit area<45 cm2

1)Sum of dimensions along any straight line<5cm

3)<t/2 (excl corrosion allowance)

t

API 510


WHAT ABOUT THIS?

API 510


A year-interval

Maximum period between on-stream inspections

= the smaller of:

½ the remaining life of the vessel (based on corrosion rate)

Or

10 Years

10 API

SPECIFIES:


THE GENERAL PRINCIPLE OF CORROSION RATE IS USED:

Remaining life (years)=Thickness(actual)-Thickness (minimum)Corrosion rate (mm/year)

Excluding the design corrosion allowance

API 510


WHAT API 510 CONSIDERS AS ‘LOW RISK’ VESSELSCorrosion history has been tracked for 5 yearsVessel not in creep rangeVessel not subjected to Hydrogen damage from the process fluidVessel is not strip or plate-lined

ON-STREAM INSPECTIONS ALLOWED(with UT thickness measurements)

API 510


Low risk vessels

Higher-risk vessels

15 years or 2/3 remaining ‘corrosion-rate life’

10 years or ½ remaining‘corrosion-rate life’

A general acceptance that on-stream inspections can be used

API 510


IF A VESSEL IS MOVED OR ITS USE CHANGED:

API 510 specifies that an inspection needs to be done

(but the extent of this inspection is up to the user)

API 510


SUMMARY:SO: API 510:

Specifies principles of vessel inspections……...BUT…….leaves many

technical decisions to the inspector

API 510 is not

particularly definitive by itself

03 PPP TTE VLS AND API 510

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