First Name
Andy
Last Name
Piatt
Severity
Incident
Was Hydrogen Released?
Yes
Was There Ignition?
No
Incident Date
Apr 04, 2002
Equipment
  • Hydrogen Storage Equipment
  • Vent line
Damage and Injuries
Probable Cause
Contributing Factors
Characteristics
When Incident Was Discovered
Lessons Learned

An investigation team was formed to determine the cause of this anomaly. The team performed a fault tree analysis which identified the following five main paths or gates: fault in the original weld, age, component not built per design intent, overstress, and design error. This led to 48 events on the fault tree, all of which were investigated. The investigation, analysis and testing determined that the first path, fault in the original weld, was the primary source of the failure.

The fault tree analysis pointed to three probable and two possible contributors of the failure. The probable contributors included incorrect filler rod selected by welder, insufficient fusion in the weld, and insufficient weld penetration. The possible contributors included incorrect power level setting and incorrect heat level applied during welding.

Materials laboratory work confirmed that improper filler metal (4043 Al) was used to weld the 5083 Al alloy vent pipe. The 5083/4043 combination is not recommended for Al welding per either current or past standards. In addition, the failed weld was a very poor weld, most likely a field weld. NDE data indicated a higher number and severity of defects in this weld compared to other welds in the vent line. According to the material lab's failure analysis report, the weld failure resulted from tensile overload originating at the bottom surface of the vent line during tanking operations and was likely the result of a single overload event.

Vent line inspection was performed to identify other suspect welds. Inspection methods included the following: visual inspection, conductivity tests on both sides of each weld to identify the pipe metal (5000 or 6000 series Al), helium leak check of welds, non-destructive evaluation (NDE) using a combination of x-rays and ultrasonic testing, and silicon etch tests to identify weld material. The silicon etch test procedure was successfully developed in the course of this effort to identify 4043 weld filler material in the field.

Instrumentation attached to vent lines during subsequent operations has provided data for the ongoing weld stress analysis and screening criteria to determine which welds required clamshell repairs. Weld defect growth/propagation can now be monitored at periodic intervals.

An unexpected temperature difference of ~200 deg F between the top and bottom of the piping was found to occur during tanking operations in the same area of the failed weld. This temperature difference was responsible for the high thermal stress seen there. Data indicates that the peak stress in that pipe section occurred at about the same time that the weld failed and was higher than predicted.

Key:

  • = No Ignition
  • = Explosion
  • = Fire
Hydrogen Incident Summaries by Equipment and Primary Cause/Issue
Equipment / Cause Equipment Design or Selection Component Failure Operational Error Installation or Maintenance Inadequate Gas or Flame Detection Emergency Shutdown Response Other or Unknown
Hydrogen Gas Metal Cylinder or Regulator   3/31/2012
4/30/1995
2/6/2013
4/26/2010 12/31/1969     3/17/1999
11/1/2001
12/23/2003
Piping/Valves 4/4/2002
2/2/2008
5/11/1999
4/20/1987
11/4/1997
12/31/1969
8/19/1986
7/27/1991
12/19/2004
2/6/2008
10/3/2008
4/5/2006
5/1/2007
9/19/2007
10/31/1980
2/7/2009 1/24/1999
2/24/2006
6/8/1998
12/31/1969
2/7/2009

9/1/1992
10/31/1980

10/3/2008  
Tubing/Fittings/Hose   9/23/1999
8/2/2004
8/6/2008
9/19/2007
1/1/1982 9/30/2004
10/7/2005
  10/7/2005  
Compressor   10/5/2009
6/10/2007
8/21/2008
1/15/2019
    10/5/2009 8/21/2008  
Liquid Hydrogen Tank or Delivery Truck 4/27/1989 12/19/2004
1/19/2009
8/6/2004 12/31/1969   1/1/1974 12/17/2004
Pressure Relief Device 7/25/2013
5/4/2012
1/15/2002
1/08/2007
12/31/1969        
Instrument 1/15/2019 3/17/1999
12/31/1969
2/6/2013
    11/13/73    
Hydrogen Generation Equipment 7/27/1999     10/23/2001      
Vehicle or Lift Truck   7/21/2011         2/8/2011
12/9/2010
Fuel Dispenser   8/2/2004
5/1/2007
6/11/2007
9/19/2007
  2/24/2006
1/22/2009
     
Fuel Cell Stack            

5/3/2004
12/9/2010
2/8/2011

Hydrogen Cooled Generator       12/31/1969
2/7/2009
     
Other (floor drain, lab
anaerobic chamber,
heated glassware,
test chamber,
gaseous hydrogen
composite cylinder,
delivery truck)
  11/14/1994
7/21/2011
7/27/1999
6/28/2010
8/21/2008
12/31/1969
3/22/2018
    6/10/2019
  • = No Ignition
  • = Explosion
  • = Fire