Recurrent inspections of pressure vessels under cyclic ... · Recurrent inspections of pressure vessels under cyclic stress ... Agitated vessels (parts under ... No.15 Pressure vessels

150 years

Recurrent inspections of pressurevessels under cyclic stress

Hans-Ulrich MoserTechnische Anlagenüberwachung BASFBASF SE Ludwigshafen

11. Europäische Druckgerätetage30.6. – 1.7.2015

150 years

Structure

Fatigue

Technical rules

Damage mechanisms

Test methods

Example sending pressure vessel for pneumatic conveying

Example inspection concept pressure swing adsorber

Summary

2

150 yearsFatigueDefinition according to AD2000

design on staticload

continuouslyoperated

Apparatus/Reactors

Number ofload cycles10000

Agitated vessels(parts under

pressure)

Buffer vessel Kneader

..

Agitated vessels(Shaft, agitator)

MachineryPressure swing adsorber

design on limited lifespan

endurancedesign

2·106

..

Paddle dryer

3

150 years

Rules (1): Technical rules

TRB 801, No.15 Pressure vessels under cyclic stress (withdrawn):• Recurrent inspections at least after half of the calculated lifespan• Inspection prior putting into service: Identification of the most highly

stressed areas• Higher amount of inspections of welding seams during manufacturing• ........

TRBS 1201 part 2, internal inspection:• Identification of the most highly stressed areas• Inspection concept (Consideration of the occuring load cycles)• Testing on cracks e.g. by surface crack testing (penetration crack testing PT

or ultrasonic crack testing UT) • Welding seams must by inspectable, e.g. ground flush (externally marked)• Pre-service inspections could be necessary• ...............

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150 years

Rules (2): Manufacturing, designAD 2000 rules S1/S2 e.g.• Design e.g. avoidance of highly stressed areas• Manufacturing e.g. avoidance of weld stress and weld imperfections• Material• Design with low surface roughness• Recurrent inspections at least after half of the calculated lifespan• ........

DIN EN 13445-3 e.g.• Design• Calculation of lifespan• Design of the welding seams• Recurrent inspections at least after 20% of the calculated lifespan• ..........

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150 years

Influence parameters on fatigue

LoadsΔp ΔT ΔF ΔM

Amplitude of tensions

Number of loads untilrupture

Wall thicknessnotch effect, e.g. welds,shape deviatione.g. peaking

Geometry

Δσ

Average tensionMaterial

Surface roughness

Base material/ weld

MediumTemperature

6

150 years

Damage mechanism

Incipient crack

Number ofload cycles

Crack depth

Crack formation Crack pro-pagation

wal

l thi

ckne

ss

rupture

„Endurance“Fracture

mechanicalanalysis

7

150 years

Fracture mechanial analysis

Inci

pien

tcra

ckNumber ofload cycles

Crack propagation

rupt

ure

„endurance“Fracture

mech. analysis

Estimation of restlifespan

Leakage beforerupture?

Determination ofinspection intervals

Wal

l thi

ckne

ss

8

Crack depth

Crack formation

150 years

Crack test methods:Penetrating crack test (PT)

Principle: Coloured or fluorizing liquid

penetrates into cracks, crevicesor pores making them visible

Typical test arrangementUsual application:

Surface crack test for non

magnetic materials

Pressure vessels: welding seams9

150 years

Crack test methods:magnetic crack test (MT)

Principle: Formation of a magnetic field into a

ferromagnetic material. Imperfections close tothe surface create leakage flux that can beproved by fluorizing magnetic powder

Typical test arrangement:Usual application:

Surface crack test for ferromagnetic

materials

Pressure vessels: welding seams

10

150 years

Crack test methods:Ultrasonic crack test (UT)

Principle: A highly frequent ultrasonic impulse will be

reflected by a boundary

Typical test arrangement:

Advantages: Approachability from one side is sufficient Detection of imperfections is possible (position, length) Prove of cracks and weld imperfections

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150 years

Ultrasonic crack testing (UT) automatically Weld seams ground flush, marked from the outside UT-pre-service inspection of the welds (P-Scan) is necessary Internal inspection according to BetrSichV by UT (P-Scan)

from outside onstream possible (inspection concept)

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150 years

Example: Sending pressure vessel forpneumatic conveying

filling depres-surisation

conveying

time

pres

sure

Time of one cycle

Pressure amplitude0 – ca. 4 bar

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150 yearsRecurrent inspectionsExample Sending pressure vessel forpneumatic conveying

Usual inspectionconcept: Internal inspection withcrack test methods fromthe inside at highlystressed areas (MT, PT) e.g. atblock flanges, transition from thecylindrical to the conicalpart, reinforcement sheets, welds, .......

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150 years

15

Pressure Swing Adsorber (PSA) gas purification process

H2 Co-CurrentDepressurisation

Counter-Current Depressurisation

Adsorption

Feed Gas

Offgas

RepressurisationPurge

Step 1 Step 2 Step 5Step 3 Step 4

Time

Pres

sure

150 years

16

Present inspection concept

Inspection intervals3 – 5 years

Requires opening the vessel

Internal inspectionInner and outer vessel surface MT

Degradation of adsorbent when contact with humid air

Exchange of adsorbentafter 3 -5 years

Durability of adsorbent8 -15 years

conflict

150 years

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General procedure

Define operating conditions

Identify highly stressed areas

Fracture mechanical analysesfor each highly stressed area

Check minimum detectable crack size Determine load cycles until leak/ rupture

Sensitivity analysis

Influence of deviations from assumptions Safety margins

Max. allowable time between two succeeding inspection intervals

150 years

18

New inspection concept

UT from outside less sensitive Small cracks not detectable

Assessment of crack propagation assuming initial cracks equal to the smallest detectable cracks

Inspection intervalsdepending on crack growth velocity

Internal inspectionOuter vessel surface MTInner vessel surface UT from outside

No exchange of adsorbent

150 years

Inspection concept pressure swing adsorber

Internal inspection including MT of all welding seams from the inside whenadsorbent will be changed (every 15 to 20 years)

Pressure test every 10 years as a gas pressure test

Inspection of all longitudial welding seams and all butt-welds by UT fromthe outside, determined inspection interval of 2,5 years

Inspection by sound emission testing less suitable because of movementof the adsorbent particles

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150 years

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Summary

Main damage mechanism under cyclic stress: crack formation Indications to inspection intervals from technical regulations Support of the internal inspection by nondestructive crack testing

e.g. PT, MT, UT Conduction of inspection interval for inspection concept necessary Inspection concept for pressure vessels under cyclic stress is

possible

150 years

150 years

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