The Struggling Journey to Live Safely with the Zawtika Gas Turbine Compressor’s Exhaust Duct Which Operating Over the Designed Temperature Limit
Authors: Buntoengpesuchsakul Chanwith , Limsakul Chanapol , Prakitrittanon Chatchai , Phongchaisrikul Nannawat , Kijkla Pruch , - Zin Phyo , - Zay Yar , Khetdee Chanawan , Viriyasomboon Napas , - Thant Zin , - Yan Naing , Vattanajaroen Nattapong , Burik Surin , Pengsri Jumnongwit , Sapchaophraya Worrawut , Promlert Paradorn , Eadkaew Monchai 
Published: November 2020

The square exhaust duct and the improper insulation design of the Gas Turbine Compressors in Zawtika field initiated the premature failure on the duct, expansion joint and heat insulation. The exhaust duct's temperature over the limitation is considered as a severe consequence in the hazardous gas area. The valuable lesson learnt from the deviation on the safety issues that we had struggled during operation phase and the final safe condition shall be shared with other oil and gas operating asset.

The high temperature on the GTC exhaust duct was firstly assumed from the degraded external insulation. After the insulation rectification for a while, the over limit temperature was appeared again. The exhaust insulation was removed and inspected the internal duct and expansion joint. The severe crack at each duct's corner were found.

The crack on the duct's corner and expansion joint's metal frame were rectified by welding and the expansion joint's flexible parts were replaced. However, the problems continued to happen again. Maintenance team had engaged with the specialists to redesign the expansion joint's corner and facilitating the external convection.

The external exhaust duct's surface temperature was reduced significantly after the new solution implementation, but it could not be reduced to be lower than the limitation of Zone 2, T3, IIA which the maximum limit temperature is 200 degC in some area. The risk assessment had been carefully reviewed to ensure the actual risks were in the "ALARP" level and the mitigation investment was well optimized. After revisiting the ZPQ hazardous area classification, most of the locations on the ZPQ could be considered safe to be deviated to Zone 2, T1, IIA which the maximum limit temperature can be extended to 450 degC.

However, the T3 limitation was still maintain in some locations which the condensate can be accidentally leaked. The possibility of heat accumulation area under the T3 Zone had to be solved with the optimized solutions which are composed of 3 main items as follows: Install internal duct insulationReplace the sharp edge corner to curvature in order to reduce the heat stress over the material strengthInstall external fin on the heat conducted area of the expansion joint to facilitate heat convection over the high temperature zone

Three years of struggling journey would be valuable to share with the other operating assets. Previously, the risk of high temperature on the surface of exhaust duct in the hazardous area was unknown. Then it was addressed and recommended to monitor the hot surface temperature. Some other operating assets had also requested to share the optimized solution to mitigate their own problem from the similar exhaust rectangular duct design. This struggling journey can help not only Zawtika but also help the other operating assets in the industry to live safely in the hazardous area.