Explosion at a Testing Facility for a Space Rocket Engine
An explosion occurred at testing facility of a space rocket engine. The incident occurred when executing a test studying the performance of a hydrogen gas flow measuring system for fuel feeding system of the rocket. During testing of a 42 MPa high-pressure hydrogen gas flow system, an exhaust gas duct outlet was damaged; hydrogen blew out and exploded. Apparently the cause of this accident was the deterioration of the exhaust gas duct outlet by thermal stress.A test started, The hydrogen gas begun flowing. 5.8 seconds late, the internal pressure of the exhaust gas duct reached about 22 MPa and the duct damaged, causing ejection of gaseous hydrogen.7.3 seconds later, a hydrogen gas detector detected the leakage of hydrogen gas, and a breaker automatically shut. Then, after one second, the blowing off of the hydrogen stopped.12.9 seconds later, the leaked hydrogen exploded. A slate roof of the duct testing house blew off as far as about 160 m away. Just after that, the second explosion occurred at 200-300 m up in the sky.
Event Date
May 16, 1991
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The immediate cause was the embrittlement of a welding in the exhaust gas duct. More than 132 tests had been performed with high-pressure and high-temperature hydrogen gas combustion. The fact that cracks were found and repaired before, with reduction of the thickness of the duct, hints at some shortcoming in the procedures and/or in the assessment of the possible consequences of the repair, such as the reduction of the mechanical resistance of the component.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
fuel-feeding system for a space rocket engine
Storage/Process Medium
Location Type
Location description
Unknown
Operational Condition
Pre-event Summary
The exhaust gas outlet duct was 21 cm in diameter, 91 cm in length and made of stainless steel and nickel alloy. This duct had been used for five years and 132 tests had been carried out before the day of the accident. After 117 tests, some cracks had been found at the inside surface of welded parts Also more recently, after a check in August, 1990, some cracks were also found. These cracks were removed by grinding and the equipment's strength was confirmed by a pressure-proof test, an air test, and a special test. After the repair in August, 1990, the welding thickness had a maximum of 20 mm and the minimum of 6 mm.
Consequences
Number of Injured Persons
2
Number of Fatalities
2
Currency
Lessons Learned
Lessons Learned
LESSON LEARNEDIf an equipment is repaired several times, there is a possibility that its original performance has reduced. In particularly, grinding as a method to eliminate superficial cracks in a pipe reduced its thickness and possibly also its capacity to bear stresses. The tests performed after the grinding to measure the residual strength were clearly not enough to measure the ducts behavior under the real testing conditions.CORRECTIVE MEASURES(1) A flange joint was installed, to allow for the inspection of the welded part from inside. The basic material and welding material were changed. (2) An inner liner to prevent thermal stress was added.(3) A limit to the maximal number of the use was set.(4) The repair standard was reviewed
Event Nature
Emergency Action
A flange joint was installed to check the inside of the welded part, and it can be dismantled. Mother material and welding material were changed, an inner liner to prevent thermal stress was added, the limit of the frequency of the use was set, and the repair standard was reviewed.
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
JST failures database:
https://www.shippai.org/fkd/en/cfen/CC1200114.html
(accessed Dec 2023)