Failure of a Pipe a Ammonia Plant Due to Hydrogen Embrittlement
The cracking happened in an ammonia plant, started up in 1970, on the pipe leading hot synthesis gas from the synthesis convertor to the first heat exchanger. This pipe was affected by six cracks and consequent leakages, along a time span from 1978 to 1982. Following each cracking, repair/re-welding was performed. Before the last cracking, part of the pipe was replaced with a new piece. All the crack occurred at a approximately 90 degrees bend of the pipe. No serious fires occurred. The scientific article used as source (see references) reports that the design and the material adopted for the pipe was correct, and the pipe was operated within the recommended temperature and hydrogen partial pressure limits. Most of the cracks were due to hydrogen embrittlement and/or insufficient heat treatment in the welds and their heat affected zones. Additional causes were additional local microstructural aspects which were not corresponding the assumed base material.
Event Date
August 1, 1982
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The referred scientific article report the following findings:1. All six failures could be attributed to incorrect heat treatment2. Their modified microstructure failed due to hydrogen embrittlement 3. The geometric deformation in the bending caused a doubling of the stresses of the straight (and perfectly round) pipe
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
syngas pipe
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
According to the referred source, the pipe was constructed from a hydrogen embrittlement resistant steel. Operating conditions were 380C at 320 bars.
Consequences
Number of Injured Persons
1
Lessons Learned
Lessons Learned
This case shows the difficulty to guarantee the correct material specifications (composition, micro-structure, heat treatments, in-situ modification) required to avoid hydrogen embrittlement in the final large-dimension component.
Event Nature
Emergency Action
Interesting to report (as explained in the scientific article referred to) the very careful procedure adopted by the plant operator for the repair of cracks:a. The bends were jacketed and provided with nitrogen protection. The nitrogen injected at oneend of the jacket was analysed regularly at the exit end for the presence of synthesis gas.b. Ultrasonic testing was carried out on the welds and bends on the rare occasions that this was possible.c. No rapid changes of pressure or temperature during running.d. The pipe was pressure tested with hot water at design pressure after each weld repair.
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Garth M. Lawrence
Multiple Cracking and Leakage of a Hot Synthesis Gas Pipe - Leakage from multiple cracks in a synthesis gas pipe exit the ammonia converter.
Plant/Operations Progress (Vol. 5, No. 3)