11 codes

Design codes

Andrew Palmer

history of codes

examples

who writes codes

use of codes

misuse of codes

transmission of knowledge

design rules (Roman engineers, medieval masons)

explosive development of infrastructure in C19 (bridges, ships, boilers)

in the 1870s, 40 bridge failures/year in USA: one bridge in four failed

after the Ashtabula bridge failure (80 dead), the ASCE said that the design “violated every canon of our standard practice”

engineers developed an idea of ‘good practice’, good practice needed to be identified, written down, and kept up to date in a systematic way

a code is a statement of minimumrequirements for the protection of the community

a code is a statement of minimumrequirements for the protection of the community

a design may satisfy a code but still be a bad design:

wasteful

ugly

difficult to construct

difficult to maintain and operate

difficult to decommission at end of operating life

incompatible with sustainability

environmentally harmful

a code is a product of human beings, and therefore may contain

special interests

mistakes

inconsistencies

Do

pi

Di

po

22

22)(

io

iooiH

DD

DDpps

−+−=

BS 8010 Part 3 4.2.5.1says

Do

pi

Di

po

s p pD D

D DpH i o

o i

o io= − +

−−( )

2 2

2 2

correctly

A

F

Z

T 2

2

1000 +=τ

BS 8010 Part 3 4.2.5.3says

F

T

A cross-section (m2)T torque (N m)F shear force (N)Z section modulus (m3)

A

F

Z

T 2

2

1000 +=τ

BS 8010 Part 3 4.2.5.3says

F

T

A cross-section (m2)T torque (N m)F shear force (N)Z section modulus (m3)

pipeline designed to ANSI B31.4

only meets pressure conditionignores conditions on longitudinal stress and strain

pipeline designed to ANSI B31.4

an independent design audit pointed out that the design only meets pressure conditionit ignores conditions on longitudinal stress and strain

the owner looked for a second opinion

pipeline designed to ANSI B31.4

only meets pressure conditionignores conditions on longitudinal stress and strain

is there any code it does meet?

does it meet ANSI B31.4 code? no

does it meet UK code? no

does it meet Dutch code? no

does it meet Norwegian code? no

does it meet Canadian code? maybe

these are examples of errors and misuse

a more controversial question is whether a code should be written so that it can be used as a cookbook

we have a lot to learn from cookbooks

if you want to bake a good cake, a good cookbook may be the right way to go

if you want to build a good pipeline, a good cookbook may be the right way to go

(examples in Journal of Pipeline Engineering, 6, 69-74 (2007))

“40 g butter; 30 ml flour, 300 ml hot milk, 4 eggs, 85-115 g finely grated cheese; salt and pepper; cayenne; grated nutmeg.

“Melt the butter and cook the flour in it without letting it colour. Remove from the heat and gradually add the milk, warmed if you are a novice cook. Simmer gently until the sauce is smooth and thick – about 10 minutes. Remove from the heat and let the sauce cool a little.

“Separate the egg yolks and whites very carefully. Beat the yolks until thick and pale. Add them to the sauce and beat them in well. Then stir for a few minutes over a low heat, adding the cheese and the seasonings: salt, freshly ground white pepper, just a few grains of cayenne and a very little nutmeg. Let the mixture cool to lukewarm.

“In a bowl that’s absolutely clean and dry beat up the egg whites quickly until they stand up in soft glistening peaks that hold their shape: don’t overbeat them or they will become dry and grainy, and lose their lovely gloss. Use a rotary egg whisk, or,better still, an old-fashioned balloon wire whisk to get the maximum aeration. Sir a couple of tablespoons (30 ml) of the whisked egg white into the cheese mixture and then, very lightly and quickly-but-thoroughly, fold in the rest so that they are blended in evenly but have not lost any of the air you have trapped in them. I find it easiest to do this with a rubber spatula….”

a great number of codes are around:

ANSI B31.4 and 31.8

API RP 1111

Norwegian DnV OS-F101 (2007), but also 1976, 1981, 1996, 2000

British BS 8010 Part 3

Netherlands NEN3650

German, Danish, Canadian, Australian .....

ISO 13623

old pipeline codes

based on allowable stresses found satisfactory by industry experience

new pipeline codes (since about 1985)

follow other civil engineering fields

based on limit states that threaten continued safety or operability

limit state design is level one structural reliability, but some recent influence from level two

limit states

SLS serviceability limit state, makes pipeline inoperable

ULS ultimate limit state, compromises integrity

includes

FLS (fatigue)

ALS (accident)

acceptable failure probability is higher for SLS than for ULS

safety classes

combine three factors:

contents

A water-basedB flammable/toxic liquidsC non-flammable non-toxic gasesD natural gasE other flammable or toxic gases at

atmospheric pressure/temperature

location

2 on platform1 otherwise

temporary or permanent

fluid A,C fluid A,C fluid B,D,E fluid B,D,E

location 1 location 2 location 1 location 2(platform) (platform)

temporary low low low low

permanent low normal normal high

higher safety classes correspond to higher values of safety class factors γsc

characteristic yield strengthf SMYS fy y temp U= −( ), αcharacteristic tensile strengthf SMTS fu u temp U A= −( ), α α

fy,temp and fu,temp are temperature derating

αA is for anisotropy

αU is 1 for supplementary requirement U, intended to ensure that strength is no more than 2 sd below nominal, and otherwise 0.96

test 1 pipe sample out of test unit min(50, lot size)

accept unit

reject unit

s>1.03

s<1.00

1.00<s<1.03 test one sample from each of 2 different pipes

both s>1.00

4 retests

one or both s<1.00

all 4 s>1.00

one or more s<1.00

s = (measured strength)/(nominal SMYS)

test 2 samples from each of 2 more different pipes

test 4 samples one from each of 4 different pipes

Strength testing scheme for supplementary requirement U

far too many codes!

creates conflicts, inconsistency, mistakes, confusion

ISO codes, Eurocodes

(review article by David Willis at OPT 2004)

an unfortunate and undesirable complication is the incorporation of supplementary documents (PD) or regional annexes which continue existing codes

linepipe

ISO 3183: 2007

API 5L 44th edition, harmonised with ISO 3183 but with two regional annexes

possible future harmonisation with EN Eurocode