Research Needs on SCC of Pipelines

Raymond R. Fessler

Stress-Corrosion Cracking (SCC) Workshop

DOT/RSPA

Houston, TX

December 2, 2003

Status of SCC

• Remains an industry-wide concern

• SCC is being managed– Probability of failures is low

• Much lower than would be expected if it were not being managed

• Probably never will be zero

– Integrity of P/L can be assured

• Cost of SCC management is very high

SCC Gap Analysis

• What opportunities are there to decrease the probability of SCC failures and reduce the cost of SCC management?

• What research is needed to take advantages of those opportunities?

STRUCTURE FOR SCC GAP ANALYSIS

1.1. AssessRisk

1.2.1.Locate

1.2.2.Treat

1.2. LocateSCC and

treat

1.3. Changeoperatingpractices

1. Existing pipeline

2.1.1.Initiation

2.1.2.Threshold

2.1.3.Growth

2.1. Selectresistant

steel

2.2. Selecteffectivecoating

2.3. Designoperatingconditions

2. New (future) pipeline

Manage high-pH and near-neutral-pH SCC

Criteria for Recommending Research

• Understanding is not high

• Probability of success is reasonable

• Potential benefits far exceed cost of research

Incentives for Additional R&D

• Improve effectiveness and reduce costs of– Hydrostatic retesting– ILI– Direct Assessment

• Make future pipelines more resistant to SCC

Objectives for Future R&D

• Optimize hydrotesting and ILI intervals– Justify on basis of crack growth rate– Extend intervals by reducing crack growth rate

through operating practices– Prioritize areas– Optimize procedures

• Develop ILI for gas pipelines

Objectives for Future R&D (cont.)

• Validate Direct Assessment for SCC

• Develop direct-examination sizing techniques

• Develop simple-to-use ECA methods

• Validate new repair methods for SCC

• Develop resistant steels

R&D Approaches

• Optimize inspection intervals– Improve crack-growth models

– Improve site-selection models

• ILI– Develop technologies

– Develop commercial tools

• Direct Assessment– Field Validation

• Sizing techniques– Develop & qualify commercial tools

• ECA methods– Develop simple tool (RSTRENG for

SCC)

• Resistant steels– Evaluate current steels

– Understand relationships between composition, structure, properties, & performance

Crack-Growth Models

Crack-Growth Models

• Several crack-growth models – Leis (Battelle) probabilistic model for high-pH SCC– Rainbow P/L Model for near-neutral-pH SCC– Beaver’s/Lambert’s superposition model

• All are based on simplified assumptions about growth rate of single crack

• Some consider interactions between cracks• Each has benefits and limitations• At least two should be examined and developed more

fully

Site-Selection Models

Site-Selection Models

• Difficult to evaluate effectiveness– Limited data– Few “control experiments”– Proprietary algorithms– Continual refinements

• Phenomenological rather than scientific

Site-Selection Models (continued)

• Mixed industry experience– Geographically specific– More reliable with tape than asphalt– Interdependent factors (e.g., coating type and soil resistivity)

• Opportunities – Develop scientific basis– High pH vs. near-neutral-pH– Improved soils module

• Accelerating & Inhibiting factors– Incorporate operating history & coating– Combine industry data

In-Line Inspection (ILI)

In-Line Inspection (ILI)

• No satisfactory commercially available tool for gas pipelines– Liquid-coupled UT too cumbersome and expensive

– Elastic wave has inadequate discrimination

– EMAT remains to be demonstrated

• Too early to judge other technologies, but probably long shots– Circumferential MFL

– Rotating magnetic-field probe

– Gas-coupled UT

In-Line Inspection (continued)

• Role of PRCI– Support field validations

– Develop/encourage/test new technologies

• Role of vendors: Develop commercial tools• Role of DOT• Protection of proprietary ideas• Assurance of adequate market

SCC Direct Assessment

(Covered in other presentations)

SCC Direct-Examination Sizing Techniques

(Covered in other presentations)

Resistant Steels

Resistant Steels: R&D Approaches & Issues

• Empirical approach– Test current and new steels

• Fundamental approach– Relate SCC susceptibility to micro-plastic behavior,

microstructure, composition, processing

• Issues– Large effort required

– Proper coatings and surface preparation provide significant benefit

Speculative Budget Projections

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Crack Growth NDE-In the Ditch ILI Site Selection DA

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Summary of Opportunities for Gov’t/Industry Cooperation

• Optimize testing/inspection intervals– Crack-growth models– Site-selection models

• ILI for SCC– Practical technologies for gas lines

• Direct-examination sizing and ECA of SCC

• Resistant-steel development