All industrial and commercial boiler deaerators are ASME Section VIII unfired pressure vessels, which must be taken offline from time to time for inspection & maintenance as required by jurisdictional authorities and/or insurance providers. The Hurst Boiler DOM DA/ST Dual Tank Deaerator combo tank is available with emergency cross-over piping which allows the surge tank to act as a temporary boiler feed system, keeping the boiler plant in operation while the DA is out of service.