The higher turbine inlet temperatures coupled with dry low emission combustors on the widely used F-class gas turbines produces high heat loadings on the stage 1, hot section components, particularly focused on the platform section of rotating buckets/blades. This paper provides a brief design and durability history overview of the platform areas of buckets. High heat loadings combined with cyclic operation, and variation in casting supplier quality, resulted in various levels of extensive cracking and high scrap rates based on prior conservative repair limits. Currently, the consensus amongst repair shops is that platform cracking extending beyond a limited area near the edge is irreparable, and the bucket/blade should be scrapped. As repair technology is ever changing and evolving, what once was a limit may now be excessively conservative. To reduce scrap frequency and increase component repair yields, newer weld filler materials and alternative welding processes were tested and evaluated. Metallurgical evaluation of various types of weld filler metals as applied to the platforms of F-Class, first stage buckets cast from DS GTD111 material were undertaken. The buckets were equally processed up to but excluding weld filler and weld process type. The bucket platform welds were then simultaneously evaluated via optical microscopy. Crack free weld repairs, conducted on engine run platforms, given the appropriate heat treatments, pre- and post-welding, can be achieved with solid solutioned strengthened Inconel 625 filler, and low volume fraction gamma prime strengthened Nimonic 263 filler using conventional GTAW. Crack free weldments or minor cracking (cracks of a small number and length) can also be achieved using Laser Cladding and/or elevated temperature GTAW with IN-738 filler metal. Surprisingly the newer weld filler metal Haynes 282 and older/traditional Haynes 230, showed evidence of hot-cracking and/or micro-fissuring (strain age cracking. A large number and length of cracks was observed when using Waspaloy as the weld filler metal. Tensile and stress rupture testing of various types of welds as applied to the platform areas were also undertaken to down-select the best filler metal. Samples were removed from the platform area of engine run buckets. Some samples were then used to obtain a baseline set of parameters of the base material. Other samples were used to test weldments of various filler metals and weld processes against those baseline values obtained. Testing of elevated temperature GTAW weldments and laser cladding with IN-738 filler metal as well as conventional GTAW with Haynes 282 filler metal produced satisfactory tensile strength and ductility properties. Elevated temperature welds using IN-738 filler were able to achieve between 76–79% stress rupture life of the base metal, while laser cladding using the same filler only yielded a 60–64% value of the base material stress rupture life. The GTAW Haynes 282 samples yielded approximately between 57–64% of the base material stress rupture life. Based on the test results, the recommended procedure for GTD111DS blade platform weld repair is to use IN-738 weld filler with the elevated temperature GTAW process.

The microstructure and mechanical properties of materials produced by Wide Gap Brazing (WGB) and Laser Beam (LBW) cladding with different blends of Mar M247 and Amdry DF-3 brazing powders were studied. It was shown that LBW Mar M247 based materials comprised of 0.6 to 1 wt. % B were weldable. The weld properties were superior to WGB deposits with the same bulk chemical composition, due to the formation of a dendritic structure typical for welded joints, and the precipitation of cuboidal borides of Cr, Mo, and W in the ductile Ni-Cr based matrix. Both materials were found to have useful properties for 3D additive manufacturing (AM) and repair components manufactured from high gamma prime precipitation hardened superalloys.

The application of advanced coal-fired heaters to heat the working fluid for a closed-cycle gas turbine provides some challenging problems for the selection of metallic heat-exchanger materials. The requirements of a working fluid temperature bf 1550 F (1116 K) at a pressure of 300–600 psig (2.07–4.14 MPa/m 2 ) necessitate the alloys used for the hottest part of the heat exchanger must possess high-temperature strength in excess of that available in widely used alloys like alloy 800. The maximum-duty alloys must therefore be selected from a group of essentially nickel-base alloys for which there is scant information on long term strength or corrosion resistance properties. The susceptibility to corrosion of a series of candidate heat exchanger alloys has been examined in a pilot plant size fluidized-bed combustor. The observed corrosion behavior confirmed that at certain locations in a fluidized-bed combustor nickel-base alloys are susceptible in varying degrees to rapid sulfidation attack, and must be protected by coating or cladding.

This paper describes the ongoing results being obtained from a joint General Electric/ARAMCO program to improve gas turbine bucket corrosion lives in desert environments involving high concentrations of alkali salts and sulfur-containing fuels. The program has involved the insertion of buckets coated with a variety of experimental or developmental coatings into several General Electric MS-5002 gas turbines being operated by ARAMCO in the Eastern Province of Saudi Arabia. Buckets coated by a variety of process techniques, such as pack cementation, physical vapor deposition, plasma spray and sheet cladding, have been evaluated during this program. Service life on some of these coated buckets has now reached approximately 35,000 hr. In general, Pt-Cr-Al pack cementation coatings have been observed to perform well, with the Pt being critical for superior long-time service.

Two nominally 200-hour tests were conducted in the General Electric Company’s Pressurized Fluidized Bed (PFB) Coal Combustion facility in Malta, NY. The purpose of the tests was to evaluate the influence of bed operating temperature and dolomite composition on the degradation of gas turbine vane and blade base alloys and protective coating/cladding systems in the effluent from a PFB. Operating conditions were as follows: 1) 1710°-1770°F (932°C-966°C) bed temperature and Pfizer dolomite (0.1 wt% sodium plus potassium), and 2) 1630°-1690°F (888°-921°C) bed temperature and Tymochtee dolomite (0.9 wt% sodium plus potassium). Brookville seam coal with 4.5 wt% sulfur, 0.3 wt% alkali, and 0.17 wt% chlorine was used in both tests. Bare nickel and cobalt-base vane and blade alloys were susceptible to hot corrosion over the entire temperature range investigated, 1100°-1600°F (593°-871°C). CoCrAlY and FeCrAlY overlay coatings showed good corrosion resistance at temperatures above 1450°F, but were susceptible to pitting attack at lower temperatures. A platinum-aluminide diffusion coating showed excellent corrosion resistance at all temperatures.

Using dynamic powder feed it is now possible to laser hardface many low grade metallic materials with high grade alloy, ceramic, and superalloy coatings. A wide variety of components from pump housings, turbine blades, oil field drilling equipment to automobile and construction equipment can be laser hardfaced with superior metallurgical results and cost savings. This paper examines laser dynamic powder feed technology applied to gas turbine and other industrial components.

Waspaloy is used extensively in gas turbine engines. Although several techniques exist for depositing Waspaloy claddings or coatings such as gas tungsten arc welding (GTAW) or low pressure plasma spray (LPPS), little work has been performed on laser cladding or high velocity oxygen fuel (HVOF) spraying of this material. Advantages of these techniques include penetration to the substrate and thinner (250–500 micrometers) deposits. This study involved characterizing the microstructure and properties of Waspaloy coatings deposited using laser cladding and HVOF spraying. It was found that totally dense, metallurgically bonded coatings having properties similar to the base metal could be formed. Proper control of process parameters avoids thermal damage to the Waspaloy base. It is felt that such coatings can offer viable restoration schemes on worn or mis-machined components.

Industrial gas turbine components are subject, in the course of their operating life, to various kinds of damages, requiring repair processes during periodical overhauling operations. Blades, in particular, suffer from creep, corrosion, wear phenomena. The majority of blade damage is currently repaired by means of manual TIG welding, with a filler metal which is often different from the blade alloy. This leads to an inferior metallurgical and mechanical condition of the repaired area as compared to the base metal. Besides, the nickel superalloys of the blades are often subject to cracking during welding operations. A process of laser welding for the repair of the airfoil tip has been introduced and optimized, to improve the characteristics of the repaired component. Powder of the same alloy of the part is used as filler metal, and the process is carried out using a Nd:YAG laser, equipped with a 6–axis CNC motion control. The original blade geometry is rebuilt by multi–layer cladding, then the blade is submitted to machining operations, NDT testing and heat treatment. The optimizing activity has been performed with the aid of microstructural characterization, chemical composition checking (by EDX microanalysis), hardness and stress rupture testing of the welded specimens.

Several fusion repair processes such as laser cladding, laser welding and gas tungsten arc welding have been taken into consideration for repairing IN738 precipitation hardened Ni-based superalloy material. Effect of heat input on weld cracking susceptibility has been studied to obtain optimum condition for crack free welds. Variations in cracking susceptibility as a function of welding heat input is discussed with reference to metallurgical characteristics of the welds.

The 60 Hz, Frame 7F engine has been in commercial operation for more than two decades now with approximately 600 Frame 7 (F, FA, FA+ and FA+e models) machines existing in North America and a total of over 1100 F-class machines throughout the world. Volatile market dynamics in the electrical power generation field continues to force power companies to identify prudent material cost reductions opportunities in their Operations and Maintenance (O&M) business. Today, there is an industry-recognized need for advanced hot gas path component repair and reconditioning capability for operators of F-Class gas turbines that can be highly cost effective with short cycle times. The first stage buckets of the Frame 7F engine are unshrouded; whereas the next 2 stages are shrouded. Out of these rotating components, the first stage buckets show the worst degradation and thus repair of these components have been a focus point for Power Systems Mfg., LLC (PSM). The technical objective is to develop a comprehensive set of repair schemes for the stage 1 buckets since these components have the highest frequency of replacement. Listed below are some of the special repair processes that have been developed for the first stage bucket: a) Acid stripping of the MCrAlY coating (and internal aluminide coating having endured 48,000 hours of service). b) High speed grinding off of the electron beam (EB) or laser beam (LB) welded tip cover plates. c) High frequency gas tungsten arc (GTA) weld repairs of platform cracks using a new and novel developed high strength yet ductile weld filler metal. d) High frequency gas tungsten arc weld attachment of new tip cover plates. e) Laser metal forming/cladding of new squealer tips. f) Rejuvenation heat treatment for buckets that have reached 48,000 hours. g) Application of new internal aluminide coating. h) Application of upgrade design features, such as platform cooling and platform undercut. i) Application of a superior MCrAlY bond coating to that of the Original Engine Manufacturer (OEM). j) Application of a vertically cracked high density (VCHD) strain tolerant thermal barrier coating (TBC). This technical paper describes the repair development process, the implementation of the different stages of the repair schemes and presents metallurgical and mechanical characteristics of the repaired regions of the component.

Volatile market dynamics in the electrical power generation field continues to force power companies to identify prudent material cost reductions opportunities in their Operations and Maintenance (O&M) business. Today, there is an industry-recognized need for advanced hot gas path component repair and reconditioning capability for operators of F-Class gas turbines that can be highly cost effective with short cycle times. The SGT6-5000F (W501FD) engine, an “F” class machine has been in operation for more than a decade now. Of importance to operators/users and owners of this gas turbine engine is the ability to recondition the turbine “hot-end section” components, in order to support maintenance requirements. The first 2 rows of blades are unshrouded; whereas the last 2 rows are shrouded. The row 1 blades show severe degradation and thus repair of this component has been a focus point for PSM. The technical objective is to develop repair schemes for the row 1 blades since this component (other than the Transition Piece (TP)) has the highest frequency of replacement, plus is the highest replacement cost per component. Special processes have been developed for these components repairs, including but not limited to: a) Acid stripping of the coating; b) Machining off of the original brazed tip cap plates; c) High frequency gas tungsten arc welding and vacuum diffusion braze repair of platform cracks; d) High frequency gas tungsten arc weld attachment or laser welding of new tip cap plates; e) Laser metal forming/cladding of new squealer tips; f) Rejuvenation heat treatment; g) Application of superior MCrAlY and TBC coating to that originally applied. This technical paper describes the repair process development and implementation of the different stages of the repair schemes, and shows metallurgical and mechanical characteristics of the repaired regions of the component.

In order to increase the engine efficiencies in small size gas turbines and microturbines, recuperators with operating temperatures over 700°C have been developed and evaluated recently. This provides challenges to materials developers and researchers for new solutions in high temperature alloys. The alloys for recuperators should have good performance in high temperature strength, creep resistance and corrosion resistance between 700∼750°C, while their cost should be kept within a reasonable range. Traditionally, clad metals by roll bonding provide both functionality and low cost solutions in demanding corrosion resistance applications and their manufacturing has been well established in large scale production. In this work, cladding technologies, particularly roll bonding, have been reviewed. Two clad metal system approaches, e.g. simple clad metal and clad metal with diffusion alloying, applied for high temperature applications are discussed. The examples of both approaches (SOFC interconnect development, catalytic converter substrate) are presented with test results. Finally, the paper presents a preliminary feasibility study of clad metal for recuperators.

Laser cladding of 0.4 mm and 0.8 mm wide knife edges made from 17-4PH stainless steel was investigated, using two types of powder and two different post heat treatments. Acceptable cladding deposits of 0.5 to 0.9 mm height were obtained on both sizes of knife edge, and with both powder types. Powder manufactured by water atomization was more difficult to feed during cladding, and produced a substantially higher oxide content in the deposited clad. The clad dimensional results showed that increasing laser energy density into the knife edges caused an increase in both clad build-up height and parent melt-back. An optimal energy density was established for a given knife edge width and powder feed rate, which produced the most efficient cladding deposit. Full solution heat treatment and aging was effective in producing a uniform hardness profile across the clad and substrate materials, while direct aging resulted in a non-uniform profile. This repair technique is applicable to a variety of labyrinth seals used in gas turbine engines.

The effect of cladding of Ti-6Al-4V knife edges using wires and a CO 2 laser power source was investigated. This method of cladding, in combination with conventional atmospheric shielding techniques, permits continuous deposition of thick (> 1mm) cladding of acceptable porosity and microstructural quality. The cladding width increased to 0.76–0.81mm irrespective of the knife edge width of 0.350–0.76mm. Continuous deposition of multiple layers was possible, at 0.125–0.150mm increase in thickness per pass, at part linear speeds as high as 762 mm/min. While the process is sensitive to practical considerations of wire feed, knife edge and laser alignment, no evidence of damage to the substrate from laser reflection was observed.