Fatigue failure of thermowells in feed gas supply downstream pipeline at a natural gas production plant

• The premature failure of thermowells was attributed to fatigue damage encouraged by improper selection of thermowell configuration.
• High flow velocity of the pipeline medium increased the wake frequency above the natural frequency of the used straight type thermowell.
• This in turn resulted in a resonance condition where massive amounts of energy were absorbed by the thermowell resulting in high stresses.
• The problem was solved by installing new thermowells with a modified configuration where truncated conical-type thermowells were used.
• This thermowell type is structurally stronger, having a higher natural frequency and a lower stress concentration than the failed one.