This paper is related to 16Mo3, a low-alloy steel typical in the manufacture of large welded steel casings of heavy-duty gas turbine engines. The usual practice in manufacturing is to stress relieve these housings after fabrication welding. If, however, weld imperfections are detected by non-destructive testing, weld repairs are performed, followed by additional stress-relief heat treatments. The methods applied were used to detect possible embrittlement by secondary carbide precipitation and to finally draw conclusions on material changes. The critical area of a weld is the heat affected zone. In this area a worsening of the stress condition in connection with a change in carbide precipitation and thus a decrease in creep rupture strength occurs. A concrete alloy composition and heat treatment adapted to the precipitation behavior are important, because they determine the type, amount and distribution of the resulting carbides [1, 2].