Part of the pipeline network used to channel nitrogen gas at a manufacturing plant has suffered a failure and ruptured. This incident took place after the refilling of liquid nitrogen from transportation vehicle into the storage tank was done. No loss of life or injury was reported because there was no worker in that area during accident.
Investigation found (revealed) that the pipelines which are made of carbon steel, ruptured in many parts during the accident. Failures on welded part of the pipeline were also detected.
Figure 1: Rupture on pipe. (a) Welding marks on the failed pipeline. (b) Welding material and pipeline material at close range. (c) Pieces of pipeline with brittle fracture failure
Recommendation of Improvement:
- Welding on critical and pressurised parts should be done by a qualified welder. The process and method of welding shall meet the requirements of relevant standards.
- Design of storage tanks and pipelines should be in compliance with the appropriate design standards and code of practice.
- Pressure safety valve shall be installed at appropriate location on the storage tanks to prevent undetected overpressure. The safety valve must also be suitable with the range of pressure used.
- Some metals become brittle when exposed to low temperature. This condition can cause failure to happen in a short period of time and without imminent warning. For this purpose, any metal used for pipelines and storage tank shall be suited to the type of gas/ liquid and operating temperature/ pressure, especially if it involves cryogenic process or materials.