A steam trap bypass tube in a power plant was totally fractured. The aim of
this study is to examine the evidence presented by the steam trap bypass tube failure,
determining the failure mechanism, determining the root cause of the failure and to
recommend appropriate corrective actions. The power plant is a coal fired power plant
with its normal operation temperature of 540°C. This study consists of failure mode
inventory collection of the steam trap bypass tube failure, collection of background
information about the process, component function and operating conditions.
Detailed investigation carried out by visual examination, nondestructive testing
(NDT), metallurgical testing which consists of microstructure examination, chemical
testing and mechanical testing. Optical Microscopy (OM), Scanning Electron
Microscopy (SEM) combined with Energy Dispersive X-ray Spectroscopy (EDS),
Glow Discharge Spectrometer (GDS) and Energy Dispersive X-ray Diffraction
(XRD) experiments were used throughout the investigation on the sample obtained.
From the evidence with considering the contribution factors such as temperature,
pressure and environment, a fault analysis was made and it can be concluded that the
cause of failure to the steam trap bypass is due to multi causes which consists of
creep failure and hydrogen damage. The root cause of high temperature creep and
hydrogen damage which occurred at the steam trap bypass tube is due to material
properties that are inadequate for the actual operating conditions of a steam trap
bypass tube which is not according to the specification. The material must be
actually ASTM SA-335-P22 (2.25Cr-lMo) with 490MPa minimum tensile strength
and 320MPa minimum yield strength. However from the investigation found that the
material used was ASTM SA-l92 (low strength carbon steel) with 324MPa
minimum tensile strength and 180MPa minimum yield strength
