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Avec plus de 30 ans d'expérience dans les services de production d'électricité et de vapeur industrielle, Tetra Engineering a une longue histoire de projets.
Tetra Engineering performed a CFD analysis of the HRSG gas path at a CCGT in Asia in collaboration with CFD specialist R&R Consult. The results showed a very uneven flow distribution at base load over the HPHTSH tube sheet, with a higher mass flow located towards the outlet header sections and towards the side walls. The swirling motion of the GT flow results in a different flow pattern for the low load case, compared to the base load case. The flow was more evenly distributed in the longitudinal direction at the SH, but a considerable variation is seen in the span-wise direction. The uneven flow distribution was thought to be a contributing factor to the repeated fatigue failures seen in the boiler over the last couple of years.
Tetra Engineering completed a Tube Failure Analysis of failed SH tubes from a CCGT plant in South East Asia. The results show the following damage mechanisms present: Short-term Creep and Fatigue damage (Creep-Fatigue interaction) Short-term Creep and Stress Corrosion Cracking (SCC) or Hydrogen Embrittlement The fact that short-term creep damage was observed on both of the failed tubes indicates a sudden change in temperature. It was possible that newly discovered damage to the turbine exhaust flow correction device could have allowed a larger mass flow to one side of the boiler (due to swirl influence), increasing the tube temperatures locally and/or increasing local stresses when expansion is prevented, thus accelerating creep damage. The plant had suffered from frequent fatigue failures, with several independent metallurgical analyses over the years confirming thermal fatigue as the previous root cause. No signs of any creep damage had previously been discovered.
Tetra Engineering was asked to assess the situation after a significant water slug/hammer event. Observations made during the site visit showed that the structural members were severely damaged with steel being heavily deformed and torn in some cases. Piping supports were also severely damaged and would require repair.
Tetra Engineering was asked by a client to help to assess the cause of tube failures in the upper section of the LPEVAP on their HRSG units. The first tube failure was reported in 2010; other failures have followed since then at a rate of two to three per year. At the time of the first failure the plant had been operating for approximately three years. Tetra performed a root cause analysis which included a review of water chemistry logs, boiler simulations using PPSD as well as a FAC Risk Assessment.
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