7EA Users Group: Discounted reg fee for the 2016 meeting expires Friday. Register today!

7EAlogoBudgets are tight. . .everywhere. But that’s no excuse for not attending the 25th anniversary meeting of the 7EA Users Group, November 1-3, at the Hershey Lodge Convention Center in scenic Hershey, Pa. The 7EA UG has the most favorable registration fee in the industry. Think of it as least-cost learning.

If you’re an owner/operator of one or more GE 7B-EA engines and not yet registered for this conference you missed the 50-buck admission ticket, but you can still get in the door for $150—or less than half of what other user groups charge these days—if you sign up by Friday.  After September 23 you’ll have to pay $250.

Participate and learn how to reduce unplanned outages by upgrading critical compressor components to mitigate clashing and other fleet issues associated with this engine. Recall that clashing is the term used to describe contact between the leading edge of stationary vane tips with the trailing edges of rotor blades at the platform. When first experienced, clashing was associated with 7EA first-stage airfoils (rotor and stator blades) but later also was identified in the machine’s second and third stages. And it has been experienced in 7FAs, 6Bs, and even Frame 5s, according to field reports.

Last year’s robust presentation/discussion program on clashing will continue this year, with the OEM likely updating the group on fleet experience with an airfoil coating to guard against destructive corrosion, the value of shorter ring segments and a corrosion-resistant ring material, testing of an IGV schedule to change the characteristic of rotating stall, a fourth-flex retune to minimize the potential for clashing, etc.

A couple of these topics are not typical of the ones you normally find on user-group programs. In some cases they require deep concentration to absorb content important to reliable operation. The editors recommend hearing this information first-hand in an environment that provides access to qualified experts—engineers from the OEM, user organizations, and third-party services providers—during breaks, meals, the vendor fair, etc, to answer your questions.

The Nov 9-12, 2015 meeting in Santa Fe, NM, was considered by some owner/operators the most significant 7EA Users Group conference they had ever attended because users finally received meaningful answers and guidance regarding the clashing and forward-compressor issues that had dogged the fleet for several years.

Detailed presentations by GE, four users, Advanced Turbine Support LLC, and EPRI on clashing experiences and investigations, together with open discussion on the topic involving many of the 115 registrants from eight countries, helped attendees better understand what they were dealing with and enabling the formulation of next steps to mitigate the issue.

It had to have been a career moment for Pat Myers, who recently retired as plant manager of AEP’s Ceredo Generating Station, a six-unit simple-cycle peaking station powered by 7EAs. Myers was the organization’s de facto chairman who relentlessly pursued answers to clashing questions brought to the floor by members of the user group at every meeting since at least 2008.

The starting point of the Santa Fe presentations and discussion was first-stage clashing, and cracking at the root (and possible liberation) of some first-stage stator vanes (S1). These phenomena were said to be caused by a rotating-stall-driven first-flex (1F) vane frequency response experienced during startup and shutdown. Suggestion to attendees: Read TIL 1884-R1, “7EA R1/S1 Inspection Recommendations,” on the importance of inspecting R1 and S1 airfoils for possible clashing damage.

The group was told that rotating stall is an unavoidable transient condition on every startup and shutdown. Further, that the stall condition is most likely to drive a response in S1 vanes when inlet temperatures are below about 50F, making engines in North America particularly susceptible. Veterans recalled that the first report of clashing by a member of the 7EA Users Group was on an especially cold December day.

The 1F frequency response, plus the loss of damping attributed to ring-segment corrosion, results in clashing. Recall that the roots of vanes in the first four rows of the 7EA compressor are inserted into slots in the ring segments and the accumulation of corrosion products in that space can lock the airfoils in place.

In sum, evidence to date points to moisture in the compressor case, cold weather, carbon-steel ring segments, and 403cb vane material (pre-1996) as the primary causes of clashing—with starts-based engines most susceptible. Clashing also is in evidence in 7EAs shipped after 1995, but the GTD450 vane material in these units has improved fatigue properties and is more forgiving when under resonance from the 1F frequency response.

Replacement of the existing six carbon-steel ring segments with a dozen segments made of Type-431 stainless steel is recommended by the OEM to mitigate vane lock-up. Increased clearance between the ring segments and casing and the elimination of shims are other positives associated with the upgrade. Roughly 10% of the global fleet reportedly has completed this work, gaining positive operational benefits.

Shortly after the 2015 conference, the OEM released TIL 1980 (Jan 20, 2016), “7EA S1 Suction-Side Inspection Recommendations,” to inform users of the need to inspect for crack indications on the S1 airfoil—in particular, units with vanes of Type-403cb stainless-steel—regardless of clashing damage on S1 and R1 airfoils.

Note that the higher-than-normal operating stresses caused by the frequency response and loss of damping described earlier reach a maximum on the suction side of the stator vane near the mid-chord location. Crack indications in this so-called “area of interest” are best identified, according to the leading third-party inspection services firm, by eddy-current inspection. Its technicians found some cracks too tight to bleed dye penetrant as recommended by the technical information letter in cases were fluorescent penetrant inspection is not possible.

In addition to the possibility of S1 liberation at the root of the airfoil or in the mid-chord area, some units—primarily those operating baseload in corrosive environments (think Middle East)—may be susceptible to S1 tip liberation. The causes here are the fourth-flex (4F) vibration mode, loss of damping, and crack initiation caused by corrosion pitting on the vane. The findings on virtually all incidents: GTD450 vane material, carbon-steel vane-segment rings, at least one pit at the point of liberation. Cracks typically initiated about 2 in. from the tip of the airfoil, moving from the trailing edge straight across to the leading edge before liberating.

One user reported that his company’s large fleet of 7EAs in baseload service had suffered a total of six individual S1 blade-tip failures in four machines during the 42 months before the 2015 meeting, but no forced outage resulted. Mitigation recommendations: stainless-steel vane rings, shot-peening to improve damage tolerance on the first seven stages of the compressor, and coating of S1-S7 stator vanes with the OEM’s proprietary GECC-1 formulation.

Considering reports, fleet-wide, of about five-score clashing events, three-dozen tip liberations, half-a-dozen root liberations, and several reports of mid-chord cracking over the last six or seven years, how can any conscientious 7EA owner/operator pass on the opportunity to attend the Hershey meeting for a progress report on the issues and their solutions?

Steering committee

Jason Hampton, senior project engineer, EthosEnergy Group
Joseph Miraya, CT program manager, Duke Energy TGS
Syed Mehdi Ali, GM operations, Karachi Electric Supply Co
Tracy Dreymala, facility manager, San Jacinto Peakers, East Texas Electric Co-op
Ronald Eldred, plant manager, Rosemary Power Station, Dominion
Michael Johnson, powerplant supervisor, Turlock Irrigation District
Guy LeBlanc, supervisor, Consolidated CT Plants, First Energy Corp
Tony Ostlund, combustion turbine technician, Puget Sound Energy
Lane Watson, account engineer, FM Global
Mirza Hossain, plant engineer, TransAlta Corp
Randall Rieder, mechanical engineer, ATCO Power

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