During　the　construction　and　operation　period,　the　induced　crack　defects　in　the　structural　components　of　steel　structures　may　propagate　and　eventually　result　in　the　fracture　failure　of　the　structural　components.　Therefore,　it　is　of　great　significance　to　assess　the　safety　of　structural　components　containing　crack　defects.　Firstly,　the　principle　of　failure　assessment　diagram　(FAD)　and　KIC　fracture　criterion　were　introduced,　which　are　based　on　fracture　mechanics,　and　on　the　assessment　method　of　SINTAP.　Then,　the　experimental　methods　for　obtaining　material　parameters　required　by　SINTAP-FAD　assessment　procedure,　and　the　calculation　methods　of　fracture　mechanics　parameters　and　plastic　collapse　loads　of　the　flawed　components,　were　presented.　Finally,　the　safety　assessment　of　crack　defects　within　the　butt　welds　on　large-size　plate　girders　of　boiler　steel　structures　from　two　power　stations　were　conducted,　using　KIC　fracture　criterion　and　SINTAP-FAD　method.　The　results　show　that　the　proposed　method　based　on　SINTAP-FAD　provides　an　effective　and　practical　approach　for　the　safety　assessment　of　structural　components　with　cracks　or　crack-like　defects　in　steel　structures.　Further　research　should　be　dedicated　to　the　assessment　method　considering　the　multiple-crack　coupling　effect.　©　2017,　Engineering　Mechanics　Press.　All　right　reserved.