in a method and system for testing the integrity of pressure vessels , or welds on flanges or the like , at elevated temperatures , a pressurized mixture of a gaseous environmentally safe composition is formed within an indicator chamber in a housing receiving a pressurized gas and containing a surface in the chamber upon which is placed an indicator composition including a marker component , whereby the marker component is carried by the carrier gas from within the chamber and through a conduit to the pressure vessel or weld area . the carrier gas and the indicator or marker component are injected in an area between the inner and outer weld of a terminal flange welded to a tubular pipe section or casing . the pressurized composition includes a marker component or sub - composition which is detected by a detection apparatus which scans the pressure vessel area to be tested , or weld area . the pressure of the gas may also be monitored to observe losses in pressure indicative of flaws in the pressure vessel area or welds . the integrity of the pressure vessel or welds is tested at elevated temperature permitting remedial repairs to be made without reheating the work area of the pressure vessel or on a tubular pipe or casing .