Cast Iron FFSA New Tool for Making Replacement Decisions

Shane Ayers

Deputy Director

Division of Utility and Railroad Safety

Presentation Agenda

History

Service life and maintenance

Study findings and CI concerns

Factors affecting CI and data collection

Overview of FFS Model

Tool use and benefits to programs like IMPs, and SAVE

History

Installation of Cast iron pipes date back to 6th century BC China for water

History

Europeans used cast iron piping for water systems throughout the 12 century AD (Renaissance period)

History

The Fountains at Versailles, built in the days of King Louis the 14th of France (1700’s), are supplied by cast iron water pipelines. The original lines are still in use today, over 300 years later.

History In America, installations of cast iron pipelines dates back to

1642

Cast iron manufacturing techniques evolved and improved over the years

Installations continued through the 1950’s and 1960’s

Approximately a 100 year span where use of cast iron piping in gas systems was heavy

After the 1960’s, cast iron installations began to drop off and other materials became more prevalent

CFR Applicable Codes Sections

§ 192.275 Cast iron pipe:

§ 192.369 Service lines: Connections to cast iron or ductile iron mains:

§ 192.373 Service lines: Cast iron and ductile iron:

§ 192.489 Remedial measures: Cast iron and ductile iron pipelines:

§ 192.557 Uprating:

§ 192.621 Maximum allowable operating pressure: High-pressure distribution systems:

§ 192.753 Caulked bell and spigot joints:

§ 192.755 Protecting cast-iron pipelines:

Groupings of Cast Iron Piping

Gray cast iron

White cast iron

Malleable iron

Ductile (nodular) iron

Alloy cast iron

ASTM A48 - Standard Specification for Gray Iron Castings

Grey vs White

The term "gray" and "white" as applied to cast iron refers to the appearance of the fracture of the casting. The gray iron fractures with a dark, gray fracture, where the white cast iron shows a light gray or almost white fracture

Predominately, grey cast iron is the most common grouping in natural gas systems

Service Life and Maintenance Cast iron piping systems have a long service life, but are

prone to certain types of failures

In contrast, newer materials such as polyethylene service life projections are not fully known

The single largest maintenance threat to cast iron pipe is corrosion in the form of graphitization

Not All Graphitization is the Same

Characteristics of cast iron graphitization play an important role is making determinations of whether a pipeline is “fit for service”

Conventional failure investigations relative to cast iron pipeline failures may over-simplify or obscure the true nature of the failure

If failures are “lumped” into categories that are too general, the greater threat and higher priority projects might be masked

For a true picture of the healthof cast iron pipelines, a moregranular and more specificfailure investigation must beconducted to facilitate a betterreplacement program.

Uniform distribution, random orientation

Graphite flake types in gray irons - ASTM and AFS standards, 100X.

Rosette groupings, random orientation

Graphite flake types in gray irons - ASTM and AFS standards, 100X.

Superimposed flake sizes, random orientation

Graphite flake types in gray irons - ASTM and AFS standards, 100X.

Inter-dendritic segregation, random orientation

Graphite flake types in gray irons - ASTM and AFS standards, 100X.

Inter-dendritic segregation, preferred orientation.

Graphite flake types in gray irons - ASTM and AFS standards, 100X.

In addition to the type of graphitization, the size of the

anomaly, spacing and interconnection properties are important factors to document and consider in a FFS model.

Other Factors Operators Should Assess if Implementing a CIFFS Model

Wall thickness

Carbon content of the vintage (Higher more prone to graphitization)

Alloy elements (higher concentrations of silicon, aluminum, titanium, nickel, and copper alloy materials are more prone to graphitization, while manganese, molybdenum, chromium, and vanadium alloys provide more stability and resistance to graphitization)

Tensile Strength

Soil conditions

Loading

Microstructure properties

ASTM A247 - Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings

Ferrite Cementite Steadite

Strength Values

ASTM A438 Standard Test Method for Transverse Testing of Gray Cast Iron

Provides methods for evaluating strength values to consider

Tensile strength (pull)

Compressive (push)

Torsional (twist)

Bending fatigue (includes shear stress)

Transverse load (perpendicular)

Hardness

Cracking CharacteristicsCircumferential vs Longitudinal

A good understanding of the mechanicalproperties of cast iron pipes is critical toachieve a realistic evaluation of thestrength of pipes in the system, and thepipeline’s current safety factor, orfitness for service.

Most Common Forms of Corrosion in Cast Iron

• Selective leaching (graphitic corrosion in gray irons)

• Pitting/Alkali attack

• Stress corrosion

• Uniform or general attack

• Erosion-corrosion

• Galvanic or two-metal corrosion

• Crevice corrosion

• Intergranular corrosion

• Corrosion fatigue

• Fretting corrosion

When Performing a CI Failure Investigation

De-alloying has subtle distinctions which may indicate a different threat than general graphitization

De-alloying is more selective, where a specific agent may affect the leaching process

General graphitization is typically linked to higher casting heat temperatures and treatments

Graphitic Corrosion

Graphitic corrosion usually occurs in three ways:

1. Surface corrosion (depth will determine whether it is harmful)

2. Plug forms in the pipe wall (pitting)

This pipe may serve for years, but if a pressure surge or water hammer (in water pipe) occurs, the plug may blow out.

3. Wall graphitization

If the pipe is subjected to a heavy earth load, or perhaps a washout under a joint, a circumferential break occurs.

Soil Factors

Type variations

Density Water tables and content Salts (brackish or high alkalis) Environmental conditions

InvestigationExtent of issue may not be visually evident

InvestigationExtent of issue may not be visually evident

Investigation Tools

Pit Gauges

Bridging / bar pit gauges

UT

Pulsed Eddy Current Broadband Electromagnetic Testing

Optical (laser and light scanning)

API 579/ASME FFS-1 describes general methods for assessing metal loss

Additional data that should be collected during investigation can be found in ASME FFS-1 (note that not all data points in this standard is applicable; foe example hoop stress and other physical characteristics of steel and cast iron will differ)

Bringing in all the Pieces

Data collected in the investigation and failure analysis (shift in process) feeds into a FFS model

The model provides Go/No Go outputs for high level risk prioritization and replacement decisions

Data fed into the model enables determinations of a safety factor for segments (similar to R-Streng calculations)

This allows operators to focus on segments with higher public safety risks first, instead of “shotgun approach”

Modeling Boundaries of conditions

Material loss

Material properties

Geometry and mesh analysis

Stress analysis

Response surface analysis

Population density (class location may be used)

Pipe characteristics (vintage, diameter, etc.) (pressure in negligible factor up to 25 psig)

External loading (soil, traffic, etc.)

Modeling

Data can be dissected, graphed, and exported into other formats to facilitate analysis of output

End Results and Efficiencies

IMP

SAVE

Prioritization for replacements

Smarter, data supported decision making

Ultimately, and most importantly, enhanced public safety!

For Additional Information

GTI Project Number 21874

PHMSA contract # DTPH56-15-T-00006

Final report issued February 15, 2018

FIN