Heavy Duty gas turbines usually have a long life—frequently much longer than the OEM advertises. All gas turbines require periodic maintenance that frequently involves gas path parts repair and/or replacement. Replacement parts are always available from the OEM, and also in many cases from third parties who reverse engineer the OEM parts. Over time, all OEM’s introduce design improvements for better parts life, higher output and efficiency, or longer maintenance intervals. These improvements usually involve improved materials, coatings, and/or cooling schemes. Frequently these improved gas path parts are actually interchangeable in complete sets with the older gas path parts of the same frame size. Unfortunately, it is hard for owners (or third parties) to understand the interchangeability, as they do not have the design records for both the original parts and the latest design parts. This is especially confusing for owners who have multiple sets of gas turbines of the same frame size, but, purchased at different time periods.
As an example, there have been over 80 different drawing numbers for a GE MS6001B since it was first introduced in the late 1970’s. In this example all later vintage designs can be retrofitted in any earlier vintage MS6001B gas turbine, as they are all interchangeable in form/fit/function, even though there have been numerous design improvements. But, in many cases, it is not “ok” to put the earlier vintage designs in later vintage production units, due to firing temperature changes over time. In some cases, it is even “ok” to mix-n- match buckets with different drawing numbers in a unit to make up a spare bucket set. Great care must be taken if mixing-n-matching gas path parts to make sure all parts are identical in materials and cooling schemes.
In most cases for the GE MS5001N thru R, MS6001A & B, MS7001 A thru EA, and MS9001B thru E models, later design hot gas path parts can be used interchangeably on older vintage units in complete sets. The GE design approach has usually been to introduce changes in small increments, such that the new gas path parts had to be interchangeable with all the other older design gas path parts. Thus, interchangeability had to be built in by design. This is a significant benefit to both customer and OEM. The OEM can produce only the latest vintage gas path parts for use in both new unit production, as well as for all spare parts applications. The owner can use this to his advantage to minimize spare parts stocking since one set can cover many units in his fleet. the GE fleet is quite large—over 2000 MS5001N thru R, over 1000 MS6001 A & B, over 1000 MS7001 A thru EA, and over 500 MS9001B thru E units in the fleet.
Similar to the discussion on the “E” class fleet above, most current vintage Hot Gas Path parts for the “F” class units can be used in complete sets in earlier vintage units. This applies for the MA6001F, MS7001F, and MS9001F class gas turbines. There are only a few cases where in the latest vintage HGP parts cannot be put directly in the older vintage units. Note this only applies thru the 0.3 versions for these models.
Other OEM’s (Siemens, ABB, MHI, Ansaldo, Westinghouse, etc.) frequently had significant gas path changes every time they introduced a newer model. Thus, in most instances, customers with these OEM’s turbines usually have difficulty trying to upgrade the gas path parts on their older vintage units.
Keeping track of all the gas path parts for multiple frame sizes and models is a daunting task for most operators. The OEM will frequently provide a “supersedures” notice when supplying spare parts. That is, if the customer orders a set of gas path parts for an older vintage turbine, the OEM may supply a later vintage design, along with a notice that the new part supersedes the older vintage part. But, this is only one set of drawing numbers—not a complete interchangeability list of all drawings for that part that have been produced. So, the customer must take the OEM supersedures notice on faith. For customers who need more help managing their gas path spare parts for their fleet of gas turbines, the Keck Group International (ww.keckgroupint.com) can help in many ways:
- Review all gas path spares in customer’s inventory for supersedures/interchangeability.
- Review maintenance intervals and parts life for any parts in the customer’s inventory.
- Review all gas path parts in any given gas turbine, to see if there are sufficient improved parts to qualify for an uprate.
- Review any third party gas path parts to see if they are suitable for the given application.
Contact information for the Keck Group International (KGI) can be found on our web site or through the link below.