peter tuft as 2885.1 launch, february 2007 1 as 2885.1-2007 pipe wall thickness

Peter TuftAS 2885.1 Launch, February 2007 1

AS 2885.1-2007

PIPE WALL THICKNESS

Peter Tuft - Wall Thickness AS 2885.1 Launch, February 2007 2

Definition: Nominal WT, tN

• The “actual” thickness• As nominated on purchase order (design)• As per mill certificates (operation)• Not less than:• Required WT plus allowances & tolerances• WT for constructability (including rounding to

standard sizes)• WT for hydrotest

• From Clause 5.4.1


Definition: Required WT, tW

• Minimum WT required for pipe in service• Greatest of WT necessary for:

• Penetration resistance• Minimum critical defect length• Stress & strain (including vehicle loads)• Fracture control• Special construction• Maintainability (eg. hot tapping)• SCC mitigation• Fatigue life• External pressure• Internal pressure • From Clause 5.4.2


• Barlow’s rule, unchanged:

• Design factor FD ≤ 0.8

• Lower values of FD at some locations:• Road & rail crossings 0.72• Pipeline assemblies 0.67• Bridges etc 0.67• Telescoped lines 0.60

• From Clause 5.4.3 & Table 5.4.3

WT for Internal Pressure, tP

tP PDD

2FDY


Design Factor

• Design factor applies ONLY to WT for internal pressure

• Meaningless to talk about design factor in any other context


Allowances, G

• Allowances make provision for loss of thickness• Corrosion or erosion• Threading, grooving or machining

• Not commonly required, except corrosion allowance for lines carrying raw well fluids



Manufacturing Tolerance, H

• Does NOT need to be added to Required WT for pipe made from strip or plate (almost all linepipe)• Manufacturing tolerances for strip or plate are very small

• May need to be added for seamless pipe• Hole may not be concentric (up to 12.5% WT)

• Still need to specify tolerance in pipe order• Covered by API 5L for almost all cases

• Special limits on manufacturing tolerance for design factors greater than 0.72 (Clause 3.2.2 (a)(v))



Putting them all together

• Figure 5.4


Don’t …

• Calculate WT based on design factor only

• Order pipe based on design pressure and worry about the rest later

• Add manufacturing tolerance (unless pipe is seamless)

• Be over-precise about penetration resistance, critical defect size, etc• Calculations for decision support, not hard

deterministic outcomes


The Design Problem

• Roma - Brisbane duplication• DN 400, 450 km• Land use ranging from rural to suburban• 15.3 & 10.2 MPa• Assume X80 pipe

• Select wall thickness for:• Remote rural areas• Pipeline parallel to rural roads & highways• Road crossings• Suburban areas• Stations


Elements of Nominal WT

• Internal pressure• Penetration resistance• Minimum critical defect length• Stress & strain (including vehicle loads)• Fracture control• Special construction• Maintainability (eg. hot tapping)• SCC mitigation• Fatigue life• External pressure• Allowances• Manufacturing tolerance• Constructability• Hydrotest


Internal pressure

LocationDesign Factor

WT, 15.3 MPa

WT, 10.2 MPa

General (R1 to T2) 0.8 7.1 4.7

Road & rail crossings 0.72 7.8 5.2

Pipeline assemblies (MLVs etc) 0.67 8.4 5.6


Penetration Resistance - Rural

• Identified threat • 20 t excavator with general purpose teeth

• Min tP = 7.1 mm• Previously showed even 4.8 mm WT is OK

for the identified threat

• No need to increase WT above tP


Penetration Resistance - Urban

• Identified threat• 30 t excavator with tiger teeth

• Min tP = 4.7 mm• Backhoe with tiger teeth could penetrate

• To resist penetration:• Require 8.4 mm for reasonable assurance• Require 11.0 mm for complete assurance


No Rupture(Critical Defect Length)

• Require “No Rupture” in high consequence areas (urban etc) (Clause 4.7.2)

• Hoop stress ≤ 30% SMYS, or• Critical defect length (CDL) ≥ 150% max hole

• Hole size from identified threat• Data in Table M3• 95 mm hole size for both points of a tiger

tooth on 30 t excavator

• Required CDL ≥ 150% of maximum hole• Must select WT so that CDL ≥ 145 mm


WT for No Rupture - 10.2 MPa

• CDL varies with WT, steel grade and MAOP• Calculate from Clause 4.8.5

• CDL for 10.2 MPa urban line:• 4.7 mm WT CDL = 55 mm• 8.4 mm WT CDL = 150 mm• 11.0 mm WT CDL = 210 mm

• 8.4 mm WT adequate for “No Rupture”• CDL ≥ 145 mm as required


WT for No Rupture - 15.3 MPa

• CDL for 15.3 MPa rural line:• 7.1 mm WT CDL = 65 mm

• 8.4 mm WT CDL = 95 mm

• 11.0 mm WT CDL = 145 mm

• Require 11.0 mm WT for “No Rupture”• CDL ≥ 145 mm as required• Only needed if line upstream of city gate

passes through T1 or sensitive locations


Stress & Strain

• Combined stress due to thermal & pressure effects at bends, stations, etc• Not relevant to this design problem• Covered later in the seminar

• External loads at road and rail crossings• Use API RP 1102 to calculate stresses due to

vehicle loads


Road & Rail Crossings

• Maximum design factor for API 1102• Includes internal pressure plus vehicle stress• 0.72 at designated crossings• 0.9 elsewhere (eg. farm vehicles in paddocks)

• More information on load sources and calculations in Appendix V

• For the sample design problem:• Pipe with tP based on 0.72 design factor

adequate


Fracture Control

• WT affects fracture initiation• Critical defect length• Penetration resistance

• Also affects toughness required for fracture arrest• Details covered later in this seminar

• For the sample design problem:• Assume no special requirements• But check after fracture control presentation


Special Construction

• Covers almost anything where there may be special requirements, such as• Above ground or reduced cover• Road, rail & water crossings• HDDs• Tunnels• Bridges• etc

• For the sample design problem:• No special requirements


Maintainability

• Usual example is provision for future hot tapping



Stress Corrosion Cracking

• SCC influenced by hoop stress• Increased WT reduces hoop stress, may

reduce susceptibility to SCC• Hence heavy wall pipe sometimes specified

downstream of compressor stations where elevated temperature also promotes SCC



Fatigue

• Fatigue influenced by stress range• Discussed in Appendix N• Increased WT reduces hoop stress, hence

also reduces absolute range of stress due to pressure cycling

• Fatigue life is long for most ordinary pipelines (>> 100 years)



External Pressure

• May be an issue for certain deep water crossings or deep HDDs

• Formulae provided in Clause 5.4.5• For the sample design problem:• No special requirements


Allowances

• Clean dry sales gas• No internal corrosion• No erosion

• Good quality external coating plus cathodic protection• No external corrosion allowance required



Manufacturing Tolerance

• ERW pipe, manufactured from strip• No manufacturing tolerance required

• For the sample design problem:• No special requirements for WT

• But note, X80 pipe and 0.8 DF will require tighter than standard tolerance in linepipe specification


Constructability

• May consider extra WT for HDDs etc• Outside scope of design problem scenarios

• No need to round linepipe WT to “standard” sizes• ERW pipe ordered in project quantities can

be rolled to any desired thickness• Station piping ordered in small quantities

may need to be rounded up to next standard size

• For the sample design problem:• No special requirements (except at stations)


Hydrostatic Test

• May reduce number of test sections by adding short length of heavy wall at bottom of long steep descent



Elements of Nominal WT

• Internal pressure• Penetration resistance• Minimum critical defect length• Stress & strain (including vehicle loads)• Fracture control• Special construction• Maintainability (eg. hot tapping)• SCC mitigation• Fatigue life• External pressure• Allowances• Manufacturing tolerance• Constructability• Hydrotest


Design Problem: Rural

ScenarioRemote Rural

Parallel RoadRoad

Crossing

Pressure: tP 7.1 7.1 7.8

Other req’d components

Nil None > 7.1 None > 7.8

Required: tW 7.1 7.1 7.8

Allowances & tolerance

Nil Nil Nil

Nominal: tN 7.1 7.1 7.8


Design Problem: Suburban

Scenario T1 General T1 SensitiveRoad

Crossing

Pressure: tP 4.7 4.7 5.2

Other req’d components

Penetration: 8.4No rupture: 8.4



Required: tW 8.4 11.0 8.4


Nil Nil Nil

Nominal: tN 8.4 11.0 8.4


Design Problem: Stations (rural)

ScenarioLinepipe

(eg. S-bend)Station Pipe

Pressure: tP8.4

(DF = 0.67)

19.2(Grade B, DF =

0.67)

Other req’d components Penetration: 8.4 None > 19.2

Required: tW 8.4 19.2


Nil21.4

(round up to Sch 80)

Nominal: tN 8.4 21.4

Peter TuftAS 2885.1 Launch, February 2007 34

Questions?

peter tuft as 2885.1 launch, february 2007 1 as 2885.1-2007 pipe wall thickness

Documents

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avfrom clause

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