A braze-cracking issue can occur with F-Class DLN 2.0 and 2.6 end cover designs. Turbines at the greatest risk are those burning unheated fuel.

Low-cycle fatigue is the primary cause of braze-joint fracture at the 4 possible braze locations on each insert location. Thermal stresses are a contributor because temperatures in the susceptible locations can cycle from 100°F to 700°F.

For fuel nozzles of OEM design, insert braze cracking creates the opportunity for gas to leak into neighboring circuits and contaminate burner-tip cooling air. This scenario can create emissions and tuning challenges, not to mention the possibility of increased flash-back potential. Flashbacks can result in nozzle damage which can lead to catastrophic failure.

These failing conditions are identified if insert replacements requirements are met and reported on at incoming inspection (pressure test). At this point, under these conditions, the industry standards are to perform a full insert replacement of each failed cover assembly.

Additionally, the currently understood industry standard for brazed insert replacements (as set forth and published by the OEM) is a maximum of 3 insert replacements per cover before the cover is deemed scrap. Each time an insert replacement occurs, .030” of material is removed from the bore to establish clean parent metal for the new braze joint.

Our team has performed extensive research and development found that the “3-and-out” strategy was only true for the original 7FA DLN 2.0 cover design and not the others.

Using the original 7FA gas turbine DLN 2.0 combustion end cover as a baseline for our assessment, which used the as-designed 5/8-11 threaded wire inserts in order to secure the outer fuel nozzles to the end cover. A minimum wall thickness, at pressure vessel requirements, had been calculated to be .078”.

It was confirmed that the 7FA DLN 2.0’s 3^rd repair cycle, the minimum wall thickness is optimally .081”. Therefore the 3 insert maximum was met.

We modeled and destructively tested the 6FA DLN 2.0 end cover which had also been assessed by the OEM to only permit 3 insert replacements.

However, we had also discovered through destructive testing and 3-D modeling of the “6FA” 2.0 cover’s internal passages, that while maintaining minimum wall thicknesses insert replacements can double over the OEM recommendations of “no more than 3 replacements allowed”.

Solution & Life Extension:

MD&A Fuel Nozzle Services found that insert replacements up to 7 repair cycles, had a minimum wall thickness at .093”.  The same is true for the 7FA DLN 2.6 since the 6FA DLN 2.0 and 7FA DLN 2.6 designs use ½-13 threaded wire inserts rather than the 5/8-11 of the 7FA 2.0 to secure the nozzles to the end cover.

Our team can extend the life of the end cover on the 6FA DLN 2.0 and 7FA DLN 2.6 past the currently understood industry standard by continuing the repair cycles until the minimum wall thickness is obtained. We have also incorporated additional machining of the cover to address the warping issue that is associated with the end covers throughout their lifetime, especially with those that are utilized in an unheated application.

Conclusions & Results:

With a new maximum of up to a final 7^th insert replacements per cover, the life expectancy of an end cover increases from the OEM claim of 48,000 hrs. to over 125,000 hrs. At an average estimated rate of repairing 4 covers every 3 years, you would not need to replace a cover for 75 years!

MD&A is a worldwide leader in the repair and refurbishment of gas turbine fuel nozzles.  Our advanced engineering expertise combined with leading-edge equipment delivers reliable, extended life for new or refurbished fuel nozzle products.

Call MD&A today for Fuel Nozzle End Cover Insert Life Extension at +1 (864) 721-4200 or use our Contact form.

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This flow test apparatus provides efficient gas turbine air/gas flow analysis and is offered by MD&A Fuel Nozzle Services.

The typical call to action is a control room combustion system alarm, or noticeable gauge increases in temperature spread or emissions creep. An alternative to a complete system nozzle teardown or replacement, this on-site flow analysis pinpoints flow variances for accurate & expedient service decisions and proper resolution.

During the on-site flow testing process, fuel nozzles can remain attached to the gas turbine end covers. Individual nozzle operation is compared with neighboring nozzles or with available benchmark data.

Portable In-Situ Flow Test Stand results can confirm or deny that a particular nozzle is the cause of non-ideal unit operation. Informed decisions can then be made for nozzle replacement, or for continued gas turbine operation. The data also serves as a specific foundation for any further investigations either upstream or downstream.

Results

MD&A experience with the flow testing is often early or mid-cycle between scheduled outages and has also been used for post-startup concerns to determine if a particular nozzle or group is within calibration.

The common goal is an immediate, recorded analysis of air and gas flow issues allowing informed service and operating decisions.

At one site where the in-situ air flow test stand was used, two combustion cans/nozzle assemblies were found with issues, permitting replacement from site spares, and gas turbine operations were allowed to continue. Suspect cans were removed for analysis and repair. Outage and extended downtime were avoided.

At another site, nozzles were operating properly but problems were identified downstream at the transition piece seals. Other site tests discovered debris in pigtail piping, disengaged seals, holes in liners or transition pieces, and crossfire tube damage.

In each case, Portable In-Situ Flow Test Stand implementation led to proper diagnosis and repair saving the user time and money!

Stay on schedule

Flow test time and labor are minimal, requiring only one flow-bench operator and one individual for manual task support. Once an area of concern is identified from unit flow charts, testing can normally be completed within one shift.

The cost savings associated with this type of flow test can range from cost avoidance for not having to perform an outage to savings from minimal downtime.

MD&A knows that ongoing and careful attention to the gas turbine combustion process is critical to both a unit’s availability and to its reliable and predictable operation. The air/gas portable flow test stand is a key offering in support of this critical owner/operator goal. The shared objective is improved unit availability.

MD&A Fuel Nozzle Services, is a global leader in the testing, repair, and manufacture of gas turbine fuel nozzles for both power generation and industrial use.

MD&A is committed to being a full-service provider to the power generation industry. Along with the Portable In-Situ Air Flow Test Stand, we can couple it with a field service Borescope Inspection for a complete investigation by our Gas Turbine Services Division.

Our commitment to excellence has earned customer trust for all turbine-generator needs. We take great pride in being a recognized OEM alternative for field testing and services, as well as critical component replacement and repair.

We continue to expand our resources of professionals, facilities, and equipment to respond quickly, properly, and accurately. We are your full-service, OEM-alternative!

Call our MD&A Fuel Nozzle Services Division today at +1 (864) 721-4200 or use our Contact form.

The post Portable In-Situ Air Flow Test Stand appeared first on MDA Turbines.

From its existing Duncan, South Carolina facility, ICS will continue to service and support GE® gas turbine Frame 5, 6, 7, and 9 fuel nozzles, including standard combustion, Multi-Nozzle Quiet Combustor (MNQC) and Dry Low NOx System (DLN) 1.0, 2.0 and 2.6 for industrial and power generation customers.

Inquiries previously directed to ICS should be forwarded to:
ICS – MD&A FUEL NOZZLE SERVICES
150 Parkway West
Duncan, SC 29334
Phone: (864) 721-4200
info@MDAturbines.com

Rest assured, while our name has changed, you will be interacting with the same people, facility and processes. We look forward to supporting your gas turbine fuel nozzle and repair requirements with the same high quality, responsiveness, and professionalism you are accustomed to and have continuously entrusted us with.

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