api 579 - a comprehensive fitness-for-service guide-a

8/19/2019 API 579 - A Comprehensive Fitness-For-service Guide-A

1/11

API 579: a comprehensi

ve

fi tness-for-service guide

Ted

L

Anderson•·*, David A. Osageb

S

mt

cluml Reliabilil •

Teclmolg

y, 1898 S Flmirort Cotm. Sui1e 235, Boulde

r

CO 80301. USA

M

M

Engineering, Sltaker

fl

eiglm.

OH.

USA

Received 4

Augus

12000; revised II Decemher 2000; accep1ed 13 Decemher 2000

bs

tract

This an iclc presents an overv iew of the rcccmly published Amc1i can Pctroleumlnstitutc (API) Recommend ed Pwctice 579, which covers

fitness-for-service assessmem of pressure equipmem in petrochemical and other industries. Although API 579 covers a wide range of flaws

isms, including local metal loss, pitting coiTosion, blisters, weld misal ignmem. and fi re damage, the emphasis of the

resent arr

icl

e is on the assessment of crack-like llaws. The API 579 p rocerlure for evaluating c.-acks

in

corporates a

fai

l

m·e

assessment

ram (FAD) methodology very similar to that in other documents. such as the British Energy R approach and the BS 7910 method. The

PI document contains m extensive compendium of K solu tions, including a number of new cases generated specifically for AP1579. In the

initi

al

release of the document. API bas adopterl ex isting reference stress solutions

fo.r

the calcul.a

ti

on of

L

in the FAD procerlure.

In

a future

elease, however, API plans to rep lace these solutions with values based on a more ra

ti

onal definition of reference stress. These revised

reference stress solutions will incorporate the effect of we

ld mi

smatch.

In

addition to the Appendices of

K

and reference stress so

lu

tions, API

579 i

nc

ludes

awen

dices that provide guidance on es

ti

mating fracture toughness and

we

ld residual stress

di

stributions. Over the next few

ears these appemUces will be enhanced with advances in technology. Recently, API has entered into discussions with the American Society

Mechanical Engineers (ASME) to convert API 579 into a

jo

int APIIASME fitness-for-service guide. © 2001 PubJishcd by Elsevier

ywo

rds: American Petroleum Institute; Pai lu

n::

assessment diagram; f:o Jaw assessment: J}itness for service; Fracture toughness; Rcfcn::m:c Slress; Residual

Stress imcosity fac1or

1. Backgrou

nd

Existing US design codes

and

smndards for pressurized

nt

provi de ru.les for the design, fabrica tion, inspec

i

on

and testing of new pressure vessels. piping systems.

and

torage tanks. These code-s do not address the fact that

u

ip

ment

degrades whi le in -service

and

deficiencies due

o degra

dation or from original fabrication may be found

subsequent inspections. Fitness-for-service FFS)

n

tS are quantitativ

e engi n

ee r

ing eva.luations,

hich are

performed to demon

strate

the str

uctural integrity

f an in-service componen t

conta

ining a flaw or damage.

American Perro.leum Institute APT) R

ecom

mended

ractice

579 [

l

has

b

een developed

to provide

guidance

co ndu cting FFS assessments

of

flaws

commonly

encoun

ered in the refining and petrochemica l industry which occur

in pressure

vesse

ls, piping, and ta nkage. However, the

can

also be

app

lied

to

flaws

encoun

ered in other industries such as the pulp and

paper

industry,

Com

:s

p

ondingaulho

r. Tel.: +1 -303-415-1475; fa.: +J-303-415-1847.

E-mail address: [email protected] (T.L. Anderson).

-0 161/001$ - see f

ron1

mauer © 2001 Published

by

Elsevier Science Lrd.

ll :

S0308-0161 01l000

1

8-7

fossil fuel util ity industry, and nuclear industry .

Th

e guide

lines provided in

API

579

can be

used

to

make run-repair

replace decisions to ens

ur

e that pressurized

equipment

contain.ing flaws that has been ident ified

during

an inspec

tion can continue to be operated safe.ly .

API

579 is intended

to supp

lement

and augment

the

requireme

nt

s in

AP

T 510 [2], APT 570 [3], and API 653

[4

): to ens

ur

e safe

ty

of plant

perso

nnel

and

the publ ic

whi le older equipment continues to

op

erate; 10 provide tech

nica

lly

sou

nd

FFS

asse

ss

me

nt procedur

es :

to

e nsure that

di:fferent serv ice

providers

furnish consistent remaining

life predictions; and to help optimize maintenance

and

operation of e) iS iing facilities to maintain avai ability of

ol

der

pl

ants and enha

n

ce lo

ng-te

nn

economic viabi

li

ty

.

In

addition. API 579 will also

be

used in conjunction with API

580

Recommended

Practice For

Risk

-Based Inspection [5]

that is

being

developed

to

provide guidel ines for

risk

asse-ss

ment,

and

prioritization f

or

inspection

and

m ai ntenance

plann ing for pressure-conta ining

equ

ip

me

nt.

The initi al impetus to

develop

an FFS standard that

cou

ld

be referen

ced

from the API inspection codes

wa

s

prov

ided

by a Joint I

ndu

stry Project

(JlP)

administ ered by the


2/11

954

T.L Anderso

n D A

Osag /lntenuuiOiwl Journal

o

Presmre Vessels and Piping 77 (2000) 953- 963

Material Properties Council MPC). The driving force

behind this development was p lant safety.

The

methodology

provided for

in

this document, together with the appropriate

API

inspection code, had to ensure that equipment integrity

cou ld be safely maintained when operating equipment with

flaws or damage, and could also be u

se

d to demonstrate

compUaoce with

US

Occupational Safery and

Hea

l

th

Administmtion OSHA) 19 10 Process Safety Management

PSM) Legislation.

mented in a

MPC

FFS TIP Consul tant

s

Report [6), and this

document was subsequently turned over to the

AP

I Commit

tee

on

Refinery Equipment CRE) FFS

Ta

sk Force charged

with development

of

the FFS standard.

In terms adopted

by

the API CRE FFS Task Group devel

oping APT 579, an FFS assessment is an engineering analy

sis

of

equipment to determine whether

it

fit for continued

se

rvice.

The

equipment may contain flaws, may not meet

current design standards, or may

be

subjected to more

severe operating condi tions than the original or current

design.

The

product

of

a FFS assessment is a decision to

operate the equipment as is , alter , repa ir , monitor,

or

replace; guidance on an inspection interval is al

so

provided.

FFS assessments consist of analytical methods to assess

flaws and damage and usually require an interdisciplinary

approach consisting

of

the following:

A review

of

the existing international FFS standards by

the members

of

the MPC

JlP

was undertaken in 199 1 as the

starting point for the development

of

a new FFS standard.

Based

on

the results of this review,

it wa

s detennined that a

comprehensive FFS standard covering many of the typical

ftaw types and damage mechanis

ms

found

in

the

re

fining

and petrochemical industry did not ex ist. In addition, the

existence of many company-based FFS methods, the

complexi ty of the technology that no single company c;m

solve on its own, and the need to gain acceptance by local

jurisdictions in the US further indicated the need for a new

standard. Therefore, the JJP decided to start the develop

ment

of

the required FFS technology that would be needed

to

write a comprehensive FFS standard for the refining and

petrochemical indus

oy

.

The

results

of

this

work

were docu-

• Knowledge of damage mechanisms/material behavior.

• Knowledge

of

past and future operating conditions and

interaction with operations personnel.

• NDE flaw loca

ti

on and sizing).

• Material properties environmenta l

effe


3/11

1:1-.

Amlcrson, D.A.

Os< ge

I

rern l iona/ Journal

o Pressure

v,ssels

tmd

Piping 77

2000) 953-963

955

ased on this definition, the APT CRE FFS Task Group

odified and greatly enhanced the initial efforts of the

MPC Jfp to produce the first edition

of

API 579.

The

PC JTP conti.nued tO prov ide valuable technical contribu

ions throughout this development effort and essentia lJy

ecame the technic

al

development

an

n of the API Task

Th

e MPC FFS JfP is s

ti

ll

in

existence and continues

o provide FFS technology development while working

ly with the needs of the API CRE FFS Task Group.

consrructed to the following codes:

• ASME

B

and PV code, Section

Vlll,

Division

1

• ASME

B

and PV

co

de, Section VJIT, Divis ion

2

• ASME B and PV code, Section I

• ASME B31.3 Piping code

• ASME B31.1 Piping code

• API 650

• APT 620.

The

overall organi zat ion and assessment procedures

in API 579 are reviewed below. This is followed by a

ore detailed discussion

of

the API 579 assessmem of

Guidelines are also provided for applying APL579 to pres

sure-containing equipmeot constructed to other recognized

codes and standards, inc

lu

ding international and internal

corporate standards.

. Overview of API 579

2.2. Organization

.1. Applicable codes

API 579 provides guidelines for perfonning FFS assess

ments that can be

useJ

in

conjun

ct

ion with the APT Inspec

ion codes (APT

510

, API 570 and API 653) to determine the

itability for continued operation. The assessmem proce

ures in t

hi

s recommended practice could be used for FFS

rerating of components designed and

APT 579 is a highly srructured document designed to

facilitate use by practitioners and to

fa

cilitate future

enhancements and modifications by the API CRE FFS

Task Group. Section I

of

the document covers: introduction

and scope; responsibil ities

of

the owner-user,

in

spector, and

eng

ineer; qualification requirements for the inspector and

engineer; and references to other codes and standards. An

outline of the overall FFS assessment methodology that is

ab le 2

erview o f flaw an

ct

dmnage assessment procedures

tion in

PI 579

3

4

5

6

7

8

9

10

I I

Fl

aw

or damage

mechanism

Brittle fractw·c

General

me

ta l loss

Loca

l

me

tal l

oss

Pitdng corrosion

Blisters and

lamina1ions

\ Veld misaJignmenL a nd

shell d i ~ t o n o n s

Crack-like f1aws

High

p ~ r a l u r e oper..ttion

and creep

Fi

re damage

Overview

Asscssmcn1 pr

oce

du r

es

an: provided to evaluate t.hc r

es

istance to briulc rr Ctun:

of

n-ser

vice

l arbon and low aJI()y steel prcssw·c vessels, piping. and storage tanks. C ri teria arc pruvided to

evaluaLe nonnaJ op-cra1ing, swn-up. upset, and shutdown condi1ions

Assessme nt procedur

es

are provided to eval uate general


4/11

956 T.L Anderson.

D A

Osag / lntenuuiOiwl Journal

o


common to all assessment procedures included in API 579 lS

provided in Section 2 of the documcm. The organization of

Section 2 is shown in ab le I. This same organization is

utilized in

aU

subsequent sections that contain FFS assess

ment procedures.

Starting with Section 3, a catalogue of FFS assessment

procedur

es

organized by damage mechanism

is

provided

in

API 579. A complete listing

of

the flaw and damage assess

ment procedures currently covered

is

shown in able 2.

These damage mechanisms can be grouped at a higher

level to foT111 a degradation class (see Fig. I). This higher

level

of

organization is usef

ul

in that it provides insight into

how the assessmem procedures

of different sections may be

combined to address complex flaws in a componen1. As

shown in Fig. I , several flaw types and d;unage mechanisms

may need to be evaluated 10 detem1ine the FFS of a compo

nent. Each section in API 579 referenced within a degrada·

tion class includes guidance on how to perform an

assessment when multiple damage mechanisms are present.

When assessment procedures are developed for a new

damage mechanism, they wi

II

be added

a.s

a

self

-contained

section to maintain the strucmre

of

API 579. Currently, new

sections are being developed to address hydrogen induced

cracking (HIC) and stress-oriented hydrogen induced crack

ing (SOHlC) damage. local hot spots, assessment proce

dures for riveted components, and creep c rack growth.

A

series

of

append.ices are provided which contam tech

nical information that can be use with all sections of API

Flaw Dimensions

Stress Analysis

I

Stress Intensity Factor

Material Toughness,

Solution, K

1

~

:

K =

Kl

r

K ~ T

Failure Assessment

Diagram Envelope

Brittle Fracture

Unacceptable

Region

I

Mixed

Mode·

Brittle

"-

..

-

..

·

-

· · · ·.

0

Assessment/ l

Fracture And Plastic

~

Collapse

Point

f)

f)

l1J

Acceptable

z

:I:

Region

( )

:::>

0

t

Plastic Collapse

l

LOAD RATIO

.

L = ,.

r

I

rys

Reference Stre

ss

Material Yield Stress,

Y

Solution, ret

l

I

Flaw Dimensions Stress Analysis

F'ig. I. Schemal ic overview of the FAD prn


5/11

1

:1 .

Amlcrson,

D A

.

Os

ge I lnrern(l(iona/ Journal

o

Pressure ssels tmd Pipi

n

77 2000)

95

-

96

3

957

able J

PI 579 appendice

s

pp

endix

Tio

le

I

Thickness.

MAWP

and membrane

srress

equati

ons r

or

a FFS as

sessment

Su·

es

s analys is overview for a FFS

assessme

nt

Compendimu of SLTess intensity factor

so

lut.

o

ns

Compendium o reference

stress

solutions

Re

sidual s

tre

sses in FFS evaluation

Material

pro

pc11

ies

for a FFS assessment

Deter

ioo·aolon and failuo·e modes

Va liclaoion

Gl ossary of 1em1.s and d e f i n i t

Technica l inqu i(ies

Overview

Equations for the

thi

cklless. MAWP . a

nd

mem

brane

stress

are

given foo

ono

s1of

lhe common

press

urized components. These e q u ~ t i o n s are

provided to

ass ist intenlational practitioners who

may no1

ha

ve access

1

ohe ASfVlE c

ode and

who

need

10 deoennine if ohe local d

es

ign

code

is

si

mi

ao

10 ohe

ASME code for w

hich oh

e

FFS as,;essoneno procedure

s

were

prim

arily

d

es

i

gned

for

Recomonendaoions for ana lysis oechoiques thai can

he

used

10

peri ol m

an FFS assessmeno

are

provided including guide

lin

es for

fi

nite element analysis

A ornpendium of snes.s

int

ensity f ~ t c t o r .soJutions for

co

mmon

press

ur:ized components (i.e.

cyl_nders. spheres. nozzle. etc.) are given. These solu1ions are used fo r 1he-assess

me

.nt of crack

like

na

ws . The solutions presented represent

Lh

e l

atest

technology and have been d e r i v e d using

the finile e.lement method in conjunction w

il

·h weigh t func tions

A com pendium o refe.rencc

stress

solutions for common pr

es

surized componen ts (i.e. cylinders,

spheres no.u.lc, e tc.) arc given. These

so

lutions

are

used fo r the ass

es

sment

of l i k e

llaws

Procedur

es

to estimate the re sidual stress fidel for dilfercnt weld

ge

mc tries are

provided; this infonnation is requ ired ror the assessment of crack like Haws

Material

proper

ies required for all FFS assessments arc provided including:

Sutngoh par.nnerers (yield and

ten

sile su·css)

Phys ical

pr

operties (i.

e.

Yo

ung

s Modulu

s,

e1

c.

f'ra.clw·e (Ough ness

Dma

for

fariguc

crack.

growth ca

kulaLons

Pao i

gue

cur

l es

(lnioiao i

on)

Mareria l

data

for coee1> analysis includ ing remaining li fe and creep cr•ck

growo

h

An

overview o

tl

le types o naws and damage

mec

hanisms

thai

can occur is pl ovide

d.

concem

rat

ing on

service-indu

ced

degl

adation

mechan

isms. T

hi

sap

pe

ndix only prov

id

es an

abridge-d

Q\

erv

iew on dama

ge

mechanisms;

API

57 1

is

cun·e

nt

ly be iog d

eve

l

oped

to provide a

definitive

refe

rence for

damage

m

ec

han isms ohm can

be

used wioh AP I

579 and

A

PI

580

n overview

of

the smdies use.d to valjdate the gene.ral and local l l o s s and the cr

ack

-like

llaw

a.c;sess

menL pro

ce

dur

es

are

pro

vided

DeH

ni

lions for common terms used throughout the sect ionsand of

AP

I 579 are given

Guide

lines

for .subm

iuing a l

e e

hni

ca

l in

qu

iry tn AP

·r

are provided. Techn i

cal

inquires will be

for

ward

ed 10 1he AP I

CRE

FFS

tas

k

grour

for

resoluoio

o

79, wh

ic

h cover

FF

S assessment procedures. The majority

f the information in the appendices covers stress analysis

echniques, material property data, and other

pe11ine111

infor

ation that is required when performing a

FFS

assessmen

t.

n overview of the appendices is provided n Ta

bl

e 3.

each flaw and damage type. A logic diagram is included in

each section tO illustrate how these assessment levels arc

interrelated. As an example, the logic diagram for evaluat

ing crack-

li

ke flaws is shown in Fig. 2. In general, each

assessment level

pr

ov ides a balance between conservatism,

the amount of information required for the evalu

at

ion. the

skill of the practitioner perform ing the assessment, and

th

e

complexity

of

analysis being performed. Level I is the most

conservative, but is easiest to use. Practi tioners usually

proceed sequentially from a Level l to a Level 3 assessment

unless otherwise directed by the assessment techniques)

if

the current assessment level does not provide an acceptable

result or a clear course of action cannot be determined.

3. Assessmem me hodology

The

API 579 FFS assessment methodology used for aU

ge y p e _ ~ is provided in Table 4.

The

organization of

h section of APT

579

that covers an assessment procedure

s consistent

wi

th this methodology. This consistent

to the treatment of damage and the associated

FS assessment procedures

fa

cilitates use of

th

e document

in

thai, if a pm ctitioner is fami liar with one section

of

the

, it is not difficult ro utilize another section

ecause of the commoo structure. This assessment metho

logy has proven to be robust for all flaw and damage types

hat have been incorporated into API 579.

Be

cause of this

ccess, when new sections

ar

e added to APT 579, the

emplate used for the development will be based on this

nt me

th

odology.

.4. Assessmem levels

Three levels of assessment are provided in API 579 for

A general overview of each assessment level and its

intended use are described below.

• Level 1 -

The

assessment procedures included in this

level are imended to prov

id

e conservative screening

criteria that

c;m

be utilized with a minimum amount

of

inspection or component information. The Level I

assessment procedures may be used by ei

th

er pl ant

inspection or engineering personnel.

•

Level

2 - The assessment procedures included in th is

level are intended to provide a more detai led evaluation

that produces results that are less conservative than those


6/11

958 T.L Anderson. D.A. Osag / lntenuuiOiwl Journal

o


Tab

le 4

API 579 FFS asse

s;men1 melho

ctology for al l damage 1

ypes

Srep l.kscriplion

Flaw t

m

tltunage mechw1ism ldentijicmion - The first step in a FFS a s s e s . ~ m e n t is to identify the tlaw type and cause of damage. FFS assessments

should

no

t be pcrfonned unless the c ~ u s e of the damage can be identified. The o riginal design and fab 1cation practices. materials of construction.

servi

ce

his tory, and environmental

cond

itions can

be

used to

a . ~ > C e r a i n Lh

e likely

cause

of the damage. Once the naw ty

pe

is idcntilicd, the appropriate

section

of

Lh is document t:an be se len

1

and a de

n whether

10 proceed

with

an

assessment

can be made

3

Data requin•mems -

The d

ata

required for

FF·s a

ss

essmen ts

depend

on

Lhe

naw t)'pc or

damage mechanism being

c \•aluated.

Dma

requirements may

include: original

equipment design

in formation

pcnaining to maintenance an

d op

era

tional hi

sto

ry

; expected

fu1Urc

s e r v i c e ~ an

d

data

specific

to

the

FFS

as.sessmem

such

as llaw

size.

s1

a

1e

of s

tr

ess

in

lhe com ponem

ar lh

e l

oca1

i

on of

1be Oaw.

and material

properties.

Da1a

re

qu

iremen1s common 10 all

FFS assessm_nt procedures are covet'ed in Sectio1 J. Data reqWrements specific lO;;. damage

mechanism

or flaw type.are covered

in

lhe seclion

comai

.ning

the con·esponding assessmem

p.1

·ocedU1'

es

4

m e . n t

teclmiques and acceptance trittria

-

Assessment techniqu-es and acceptance criteria

al'e

prov ided in each $ection. I f multiple damage

mechanisms al'e p1

esem. more than

one L i o n

may

have to he used for

the

evalua1.ion

5 Remainillg life evaluurioll -

An es1ima1e of 1he 1emaining life or limi1ing Oaw size should be made. The remain

in

g life is eslabl ished using he PFS

assessmem

procedures with

an eslima1e of

urore

damage

nne

(i.e.

con·osion all

owance

.

The

remaining l

i f

e

can be used in

conjunction with

nn

inspec tion code to establish

an inspec1io

n interval

6

Remedimion - Remedi

ation

1nerhods

are provided in

each sec1ion based

on

the

damage

mechanjsm

or

naw type..

_n so

me cases.

remediation

techniques may be used 10 control fu ture damage associated with naw growth and/or material degradat ion

7 In service

monitoring -

M.e

Lhoct

s

fo

r in-servi

ce

monitoring Hre prov ided in each

sec

ti

c.

)n based

on the

damage

mechanism or

tl

aw

type. hH;ervi

ce

monitoring may

be

U.""-d for

Lhosc

case5 where, a remaining life and inspeclion interval cannot be adequately established because of the complexi lies

associated

damage

mechanism and

serv

ice environment

8 Dnrwnenration

- The

documentation

of

an FFS asse5Stnenl s

hou

ld incl ude a record of all data and decisions made in each of the

prev

ious steps to

qualify lbe component for continued operation . Documcnlat ion r e q u i r c m e n L t•ommon to all FFS assessment procedures arc given in Section 2 of AP I

579. Spcdfk


7/11

7:1_

Andersu, , D.A. O.wge I

lnrern lfiOn l/

Journ l

of

Pressure

V


8/11

96

T Anderson. D.A. O s a . . ~ • I lnttrmuiontll Journal

of

Pr .ssure Vns< am/ Piping 77 (2000)

953 963

available options for a Level 3 assessment include:

• Method A - Level 2 assessment with user-generated

partial safety factors or a probabilistic analysis.

• Method B - Material-specific FAD. similar to R6

Option 2.

• Method C - J -based

FA

D

ob

tained from clastic - pl;t

st

ic

finite element analysis, similar

to

R6 Option 3.

• Method D - Duct

il

e teari

11g

assessment.

• Method

E -

Use

a

recognized assessment procedure.

such as R6

orBS

7910.

The

Level I as

e ~ s m e n t

is very simple screening evaluation

that can be perfonned by a qualified inspector. Level I

consists

of

a series

of

allowable flaw size curves. These

curves were gcner.ucd using the Level 2 assessment with

conservative input assumptions.

l ote

that the

APT

579

Level I asscssmcm of cracks is completely diffcrcnr than

the BS 7910 Level I iiSSessment. The Iauer is u pseudo FAD

ana lysis that is intended to maintain

ba

ckward compatibil ity

wi

th the 1980

vc1

·sion

of

the

BS PD

6493 procedure. Unlike

Level I of BS

79

10 , the APT 579 Level I assessment

requires almost no calculations.

4.

New K solu tions in AP

I 579

Appendix C contains an extensive library of stress imen

sity solutio ns for cracked bodies. Many

of

these solutions

were obtained from the published literature as well as other

assessment procedures, including

BS

7910. New

K

solutions

were also generated for inclusion in APl579. Tn particular, a

comprehensive

set of

so lutions for c racks in cy

li

ndrical and

spherical shells was recently developed [14]. Th is study

involved over 2400 finite clemem runs. Of course. there

were a number

or

existing

so

lutions for cylinders and

spheres. bm these tended to cover a limited mnge of

radius/thickness and flaw aspect ratios.

ln a study commissioned by the MPC FFS project [14),

the follow ing geometries and Haw orientations were

considered:

• Internal axial surface flaws in a cylinder.

• External axial surface flaws in a cy linder.

• Internal circumferential

sUJ:face

flaws in a cylinder.

• External c ircumferential surface flaws in a cyl inder.

• Int

er

nal meridiana surface flaws in

a

sphere.

• External meridiana surface flaws

in

a sphere.

Three load cases were analyzed:

• Uniform crack f01ce pressure.

• Linearly varying crack face pressure.

• Global bending moment (circwnfcrcntial

c r . t c k . ~

in

cyl inders).

The

first 2 load cases

ca

n be used to derive a weight func-

tion. which can be used to infer K for an arbitrary through

wall

stress

field. The procedure for generating weight func

tions from the uniform and linear crack face pressures is

outlined in Appendix C of APT 579.

The range of dimensional paramerers for the cylinder 01nd

s

ph

ere analyses is as follows:

• R;lt =

3, 5, 10. 20. 60, 100, oo.

• all = 0.2, 0.4, 0.6. 0.8.

• cia=

0.5, I. 2, 4. 8, 16. 32.

where

R

is the inside hell radius.

1

is the wa

ll

thickness.

a

is

the depth of the surface flaw. and 2c is the surface flaw

length.

Fi

g.

3

is a plot o f typical resultS from the recent analyses.

Uniform crack face pressure was applied. giving a stress

intensity solution of the following form:

5)

where p is the crack face pressure, G

0

is a dimension less

geometry fuctor , and

Q

is the flaw shape parameter:

(

a 1.

6

Q= I

1.464

6)

Note that there is a significant R 1 efl'ect on the nondimcn

sional stress intensity factor, G

0

• Consequently. using a

K

solution for a s u r t < ~ c e cmck in a flat plate when assessing a

curved shell could lead to significam errors.

The

K

solurion libmry in APT 579 will be expanded as

new cases become avai

I

able. Currently. solutions for cy lin

ders

wi

th R 1 = I arc being computed.

ln

the ncar future. K

so lutions for cracks at structural discontinuities such s

noz2eles

and stif

fe

ning rings

wi ll be

generated.

5. Fractu

re

tough

ne

ss estimation

Appendix F of API 579 eo mains information

on

material

properties. including 10ughness. This appeodix does not

contain a database of toughness values, however. Rather.

it provides correlations and estimation methods. For ferritic

steels, there are lower-bound co

rre

lations of toughness to

Charpy transition temperature. These correlations were

adapted from Sections lTl and Xl of the ASME boiler und

pressure vessel code. For static loading in the

~ b s e n c e of

dissolved hydrogen. the lower-bound toughness corre

la

tion

is as follows:

K

1

c

= 36.5 3.084 exp[0.036(T-

T cr +

56))

(

MP-a../iii.

oq.

K

1

c

= 33.2 2.806

cxpt0.02(T- T .r

100)]

(7a)

(7b)


9/11

1

:1-.

Amlcrson,

D A

.

Os

lalion for hydrogen charged steels is as follows: If dissoh•ed hydrogen is

resent it may degrade the ma terial s ahility to resisl brittle frac ture

io

n.

Once

mpid

crac

k

pr

op

agat

i

on

b

egins

h

owever

l

hc

hydrogen

can no

l

onge

r inlluencc the 111atcrial

beha

vio r.

Th

erefore, the cr•ck

a r r e ~

tough

ss should e a reasonab le lower bound estitnate of the mate1iaPs ability

o

re

sist un

able crack propagation .

bution with two of the three parameters specified:

[

B

K - 20)

4

]

F = I - exp - - -- ~ c (lllJll, MPaJffi), (9a)

2;,.4 20

[ (

K)c

-

18.2 )

4

] . .

F

=

I - exp

-8

Ko

_

18

_2 (m., k

s1v111

.),

(9b)

where F

is

the cumulative probability. 8 the specimen thick

ness (crack front length), and K

0

is the Weibullmean tough

ness, wh i ch corresponds to the 63rd perceotile value. The

temperature dependence

of

the median (50th percentile)

toughness is given by

KJ

c{median) =

30 + 70 exp[

O.OI90(T-

To)] (MPaJffi, C),

( lOa)

KJc

{

rn

cdiun

1

= 27 + 64 exp[0.0106(T -

To)]

(ksi.Jin., "F

,

(

lOb

)

where To is the index transition temperature material for the

material

of

interest.

It

corresponds to the temperature at

which the median tOughness for a 25 mm ( l in.) th ick speci

men is I00 MPaJiil (9 1 ks i.Jin.). The median and Weibull

mean are related as follows:

Ko=

KJc(mcdi.m) - 20

+20 (MPaJiU),

(

Ia

)

[ln(2)]0

25

Ko=

Kk(median) - 18.2

+ L8.2 (ksiJin.). {II b)

[I

n (2)

025

By combining Eqs. (9a), (9b), (lOa), ( lOb) and (

II

a), (

lib),

we see that once T

0

is known, the toughness in the transition


10/11

962

T Anderson. D.A. O s a . . I

lnttrmu

iontll Journal

of

Pr.ssure Vns< am/ Piping 77 (2000)

953-963

region is completely described. ASTM E 1921 -98 outlines

the procedure

for

determining To from fmcrure 10ughness

test ing in the transition region.

When fracture 10ughness testing is not feasible.

To

can

be

esti

ma

ted from the 27

J

(20 ft-lb) rransition temperature:

T

o=

T

2

J -

18°C. (12a)

To

=

T

o

- 32.4o

F.

( 1

2b

Th

e above correlation has a standard deviation of approxi

mate y I5°C (2'PF).

6. Refer ence

c s . ~

and we ld mis

match

Appendix D

of

API 579

co

ntains reference stress

so

lu

ti

ons for a variety ofcracked bodies. Fo r the most part , these

solutions were adopted directly from

R6

and BS 79 10 and

are bascu on limit loau so lutions.

Th

e authors believe that the current uefinition of refe r

e nce stress based o n li mit load is inappropriate and should

be

replaced in the long run. When rigorous c lastic- plastic J

l u t i o n ~ f

or

cr;1cked bodi

es

are plolted in terms

of

FADs.

the resulting curves exhibit a strong geometry dependence

when 4 is compute


11/11

1:1..

Arukmm

V.A. Osu qe l lfl lenwtionfll

Jounwl

ofPressure Vessels und f>ipi11g 77 2000) 9SJ - 96J

963

rojec t will ;tddress the following issues:

• Confirmation of some of the parametric distributions in

Appendix

E.

• A c l

ea

r criterion for electing

'be

ndin

g'

and 'self-

equ

ili

brating' type· of residual stress distributions in pi

pe/

vessel welds.

• Development o f improved residual stress distributions

for fillet welds at comer joints. nozzle welds. and repair

welds.

• Tncorpomti on of local post-weld heat treatment e lfects.

Appendix

E

will continually be expanded and revised as

new results become available.

8. API and ASME FFS ac t

ivities

T

he

American Society of M

ec

hanical Engineers (ASME)

has formed a new main

comm

ittee, the Post ConsmJC tion

Mai.n Committee. with

a

chart

er to

develop codes and stan

dards for in-service pre

ss

ure

co

ntaining equipment

cover

i

ng

all industries. Curre ntly. standards development activity is

underway in the areas

of Ri

sk-

Base

d Inspection (RBI) and

repair methods (e.g. le

ak

seal ing. boxes, patches. etc.).

Tn the area of FFS. A

PI

and ASME are working to create a

new standards comminee that will jointly produce a s ingle

FFS standard in the US thai c;m be used for pressure

containing equipment.

It

is envisioned

that

once the nego

tiations and opemting procedures for the new committee

srrucrure

arc

complete. API

579

will form the basis

of

the

joint APIJASME stand;trd that will be produced by this

committee. The

inili

api 579 - a comprehensive fitness-for-service guide-a

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