Internal Damage Accumulation and Imminent Failure of an Industrial Gas Turbine Blade: Interpretation and Implications

Abstract

The row 1 blade from a heavy industrial gas turbine has been examined after ∼21,000 fired hours to assess the level and nature of the damage originating from the cooling holes. This consisted primarily of creep cracking/voiding coupled with deep internal oxidation/nitridation. The difficulties the manufacturer had in addressing the problem are discussed within the context of component assessment methodologies and the ‘new’ technologies which are being incorporatd into new unit types, but for which little service experience has yet been generated.

Gas turbine hot section components: The challenge of ‘residual life’ assessment

“…As has already been noted, some blade designs show cracking initiating at the inner surfaces, with these leading to blade failure in some cases (see Fig. 6 of reference [1]). Generally, although the observations are often not quantified in detail, they are exceptionally informative.…”

“…Design capabilities have improved continuously over this period of time in areas such as computational fluid dynamics and material behaviour models and data. However, this notwithstanding, there are recent examples where design failings and/or shortcomings have resulted in failures (GE Frame 6B [1]), shortened lives (Siemens V94.2 [2]) or damage restricting the potential for life extension (Westinghouse 501D5 [3]) for row 1 blades. While such design shortcomings are not exactly unique, the specific character of these (e.g.…”

Assessment and Monitoring Requirements for Industrial Gas Turbine Hot Section Components

“…Some of these points can be illustrated by reference to the recent problems encountered with the row 1 blading of a 40 MW heavy duty industrial gas turbine. The problem has been considered in more detail elsewhere (Wood 1996) but the main points are summarised in the following two sections.…”

“…The type of damage seen in the blade led the OEM to coat the internal cooling pannsges to protect them from attack. For a variety of reasons (see Wood 1996) this course of action was open to question at the time and it was recommended in 1993 that the performance of the new design be carefully monitored to see how it performed.…”