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Natural Gas Pipeline Accident Investigations – Perspectives and Recommendations. John B. Vorderbrueggen, PE Chief, Pipeline and Hazardous Materials Investigations WRGC August 20, 2013. A Short NTSB Overview. How old is the NTSB? 30 years 39 years 73 years 87 years 95 years.

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natural gas pipeline accident investigations perspectives and recommendations
Natural Gas Pipeline Accident Investigations – Perspectives and Recommendations
  • John B. Vorderbrueggen, PE
  • Chief, Pipeline and Hazardous Materials Investigations
  • WRGC August 20, 2013
a short ntsb overview
A Short NTSB Overview

How old is the NTSB?

  • 30 years
  • 39 years
  • 73 years
  • 87 years
  • 95 years
origin of the ntsb
Origin of the NTSB
  • Air Commerce Act of 1926U.S. Department of Commerce shall investigate aircraft accidents
  • 1940 - Investigations assigned to the Civil Aeronautics Board Bureau of Aviation Safety
origin of the ntsb1
Origin of the NTSB
  • 1967 - NTSB embedded in the U.S. Department of Transportation
  • 1974 - NTSB reestablished as an independent, Executive Branch agency
  • U.S. Code Title 49, Chapter 11
ntsb improvements
NTSB Improvements
  • 1996 – Coordinate assistance to families of aviation accident victims
  • 2000 – Created the NTSB Training Academy (NTSB Training Center)
    • GW University Campus in Ashburn, VA
    • Improve employee technical skills
    • Provide investigation expertise to industry
ntsb features
NTSB Features
  • Independent Federal Agency
  • Does not regulate transportation equipment, personnel, or operations
  • No official role in establishing and enforcing industry regulations
  • Does not initiate enforcement action
  • Issues and tracks Recommendations
ntsb transportation modes
NTSB Transportation Modes
  • Aviation
  • Marine
  • Highway
  • Railroad
  • Pipeline and Hazardous Materials
other ntsb offices
Other NTSB Offices
  • Research and Engineering
    • Safety Research and Satirical Analysis
    • Vehicle performance
    • Vehicle recorders
    • Materials laboratory
    • Medical Investigations
other ntsb offices1
Other NTSB Offices
  • Administrative Law Judges
    • “Court of appeal" for airmen, mechanics or mariners for certificate actions
    • Hear, consider, and issue initial decisions on appeals
    • Adjudicate claims for fees and expenses from FAA certificate and civil penalty actions
the ntsb board members august 2013
The NTSB Board MembersAugust 2013

Hon. Deborah A. P. HersmanActing Chairman

Hon. Robert L. Sumwalt

Hon. Christopher A. Hart

Hon. Mark R. Rosekind

Hon. Earl F. Weener


Natural Gas Transmission Pipeline Accidents

San Bruno, California

Palm City, Florida

Pacific Gas and Electric Company Natural Gas Transmission Pipeline Rupture and Fire San Bruno, CaliforniaSeptember 9, 2010

Claremont Drive

Earl Avenue


Glenview Drive

accident consequences
Accident Consequences
  • Eight fatalities
  • Dozens injured
  • 38 homes destroyed
  • More than 70 homes damaged
ruptured pipeline details
Ruptured Pipeline Details
  • 30-inch diameter, 0.375-inch wall
  • Installed in 1956
  • API Grade X42, carbon steel
  • Documents listed seamless pipe
  • Other inaccurate fabrication records
events prior to the rupture
Events Prior to the Rupture
  • Electrical maintenance work at Milpitas Terminal
  • Power supply units interrupted
  • Line discharge pressure climbed
accident event timeline
Accident Event Timeline
  • 5:45 p.m. pressure rose above 375 psi
  • 6:11 p.m. pipeline ruptured when pressure reached 386 psi
  • 7:30 p.m. upstream valve closed
  • 7:46 p.m. downstream valves closed
undocumented configuration
Undocumented Configuration

North joint

Earl Ave

Pup 6

Pup 5

Pup 4

Glenview Dr

Pup 3

4½ feet

Pup 2

Pup 1

3½ - 4 feet each

South joint

Rupture initiation






comparison of pipe attributes
Comparison of Pipe Attributes


  • No record of material supplier, material pedigree, or fabrication records


typical dsaw seam weld
Typical DSAW Seam Weld

Raised weld reinforcement

Outer wall

Weld metal

(first pass)

Weld metal

(second pass)

Inner wall

Raised weld reinforcement


incomplete pup 1 seam weld
Incomplete Pup 1 Seam Weld

Fracture through weld

No weld reinforcement

Outer wall

Fit-up angle

Unwelded region

Inner wall


identified safety issues
Identified Safety Issues
  • Multiple deficiencies in PG&E operationspractices
  • Federal and state regulatory oversight weakness
  • Deficient federal pipeline safety rules
other shortcomings
Other Shortcomings
  • PG&E integrity management, threat identification, record keeping, dispatch procedures
  • CPUC hydrotest exemption for pre-1961 pipelines
  • DOT grandfather hydrotest exemption for pre-1970 pipelines
probable cause
Probable Cause

Inadequate quality assurance and quality control in 1956 pipe relocation

  • Substandard longitudinal pipe joint with a visible weld flaw that grew to a critical size
  • Pipeline ruptured when poorly planned electrical work at the Milpitas Terminal caused an unplanned pressure increase
probable cause cont
Probable Cause (cont.)

Inadequate pipeline integrity management program

  • PG&E failed to detect and repair, or remove the defective pipe
probable cause cont1
Probable Cause (cont.)

Contributing to the accident

  • CPUC failed to detect the inadequacies of the PG&E pipeline integrity management program
probable cause cont2
Probable Cause (cont.)
  • California Public Utilities Commission and the U.S. DOT exemptions from pipeline pressure testing of existing pipelines
    • Hydrotest would likely have identified the installation defects
probable cause cont3
Probable Cause (cont.)

Contributing to the severity of the accident

  • Lack of automatic shutoff valves or remote controlled valves
  • Flawed PG&E emergency response procedures
  • Delay in isolating the rupture
pre report recommendations
Pre-report Recommendations
  • Pipeline and Hazardous Materials Safety Administration (2 Early, 1 Urgent)
  • California Public Utilities Commission (3 Urgent)
  • Pacific Gas and Electric Company (2 Early, 2 Urgent)
final report recommendations
Final Report Recommendations
  • The U.S. Department of Transportation (4)
  • The Pipeline and Hazardous Materials Safety Administration (13)
  • The State of California (1)
recommendations cont
Recommendations (cont.)
  • The California Public Utilities Commission (2)
  • The Pacific Gas and Electric Company (8)
  • The American Gas Association and the Interstate Natural Gas Association of America (1)
pipeline details
Pipeline Details
  • 18-inch diameter carbon steel, 0.25-inch wall thickness, API 5LX, 1959 installation
  • Hydrotested at 1085 psig
  • 1971 hydrotestedat 1320 psig - 866 psig MAOP
pipeline details1
Pipeline Details
  • Polyethylene tape coated and cathodically protected
  • 2004 Magnetic flux leakage in-line inspection
  • Postaccident metallurgy identified replaced segments but no record of the change
pipeline configuration
Pipeline Configuration
  • Three parallel, interconnected lines
  • Dual pressure-reducing regulators protected lower MAOP on 18 inch line
  • Normal flow demand (pressure) fluxuations expected
system response to the rupture
System Response to the Rupture
  • Line break actuator closed upstream ASV within two minutes
  • Downstream actuator failed to activate
  • FGT crew closed valve two hours later
post accident system test
Post-Accident System Test
  • Downstream ASV operated as designed
    • Rate-of-pressure drop setpoint was most likely above the accident pressure decay rate
    • Pressure decay dependent on looped system interaction
scada system
SCADA System
  • No position indication on mainline valves or cross-connect regulators
    • Controllers were unaware of ASV closure and the full-open regulators
    • No alarms sounded
    • Pressure scan rate too low to detect short duration pressure drop
postaccident pipe i nspection
Postaccident Pipe Inspection
  • No internal corrosion
  • External corrosion pitting under damaged coating
    • 30 percent wall thinning along longseam, below minimum required
    • Magnetic particle inspection identified longitudinal cracks along longitudinal weld
class location
Class Location
  • Ruptured pipe assigned Class 1, no HCA sites
    • Integrity management not required
    • Baseline in-line inspection was performed
    • Mainline valve spacing for Class 1
    • Class 3 applied - school within 366 feet
integrity management program
Integrity Management Program
  • Stress corrosion cracking was not considered a significant risk
    • 2004 caliper tool and axial MFL in-line inspection – no repairs required in rupture area
    • Axial MFL does not accurately detect longitudinally oriented stress corrosion cracking
fgt postaccident actions
FGT Postaccident Actions
  • SCADA instrument upgrades on looped systems
    • Pressure transmitters installed at regulators and each parallel line
    • Valve position sensors installed on regulators and cross-connect valves
    • Remote control functionality added to the cross-connect valve
fgt postaccident actions1
FGT Postaccident Actions
  • SCADA pressure rate-of-change alarm configuration revised
    • Conducted circumferential MFL inspection
    • Hydrostatic pressure tested the line – four failures on the 18-inch pipeline
    • Follow-up hydrostatic spike test
probable cause1
Probable Cause

Pipeline failed due to environmentally assisted cracking under a disbonded polyethylene coating that remained undetected by the integrity management program

The integrity management program incorrectly identified the pipe section as not a high consequence area

probable cause cont4
Probable Cause (cont.)

Contributing to the prolonged gas release was the inability of the pipeline controller to detect the rupture due of limitations in the SCADA system and the configuration of the pipeline.

ongoing investigations
Ongoing Investigations
  • Cleburne, Texas

Enterprise Products Operating, LTD

June 7, 2010

One Fatality

  • Sissonville, West Virginia

Columbia Gas Transmission

December 11, 2012


The NTSB PerspectiveMost Wanted List – Pipeline Safety

  • PHMSA and State regulators must improve industry oversight
    • effective performance-based standards
    • adequacy of integrity management and inspection protocols
    • ensure deficiencies are promptly corrected

Pipeline Safety (cont.)

  • Operators need to improve emergency response
    • Faster leak isolation using automatic and remote shutoff valves
    • Provide key information on pipelines to local jurisdictions and residents
John B. Vorderbrueggen, PE

Chief, Pipeline and Hazardous Materials Investigations