Steam Turbine Nozzle Chambers and Casing Weld Repairs

Mechanical Dynamics & Analysis (MD&A) performed Nozzle Chambers and Casing Weld Repairs on a 580 MW Westinghouse® Steam Turbine and returned the equipment ahead of contract schedule.

Repaired Flow Guide Installed and Upper Half Casing Ready for Final Assembly Check

Upon initial examination, significant issues were revealed with the HP inner casing, nozzle chambers, and selected components, all critical for proactive maintenance and long-term operation.

This 3600-rpm machine contains a double-flow HP (high pressure) turbine element, a double-flow IP (intermediate pressure) turbine element, and two double-flow LP (low pressure) turbine elements. The HP inner casing consists of 8 inlets, 4 per half.

MD&A’s Turbine-Generator Repair Facility team focused on the repair and restoration of the damaged steam turbine nozzle chambers, upper and lower half inner casings, and the center flow guide.  Various moderate erosion, fretting, and impact moderate damage was found on all nozzle chambers, nozzle plates, and inner casings.  All nozzle chamber flexplates were fractured and broken.  The B2 and C3 nozzle chambers inlet pipes were fractured from the inlet snouts and these two nozzle chambers were floating loose within the inner casing.

Nozzle Chambers

B2 nozzle chamber work called for the replacement of the fractured inlet pipe end, repair of horizontal and vertical face fretting damage, repair of admission-side impact damage, repair of broken and fractured axial locating fits, and repair of the nozzle plate eroded partitions, including all post-repair NDE inspections.  Wall thickness UT (Ultrasonic) inspection evaluated the remaining wall thickness due to the admissions-side impact damage using ASME® Codes.  The axial locating fits and other areas received weld restoration and machining, as needed.  MD&A Experts then supplied and join-welded the new nozzle-chamber inlet pipe end and prepared the chamber for reinstallation and welding into the casing.

B2 Nozzle Chamber – Nozzle Partition Repairs In Process

The C3 nozzle chamber first required the removal of a broken and lodged bell seal and retaining nuts from the inlet pipe, lodged behind the nozzle plate.  The fractured inlet pipe end was then removed, followed by repair of horizontal and vertical face fretting damage, repair of broken and fractured axial locating fits, repair of the nozzle plate eroded partitions, and repair of the nozzle plate seal grooves, including all post-repair NDE inspections.  MD&A Experts then supplied and join-welded the new nozzle-chamber inlet pipe end and prepared the chamber for reinstallation and welding into the casing.

C3 Nozzle Chamber – New Pipe End Join Welding

C3 Nozzle Chamber – New Pipe End Join Welding

Inner Casings

For the lower half inner casing, MD&A Experts replaced various horizontal joint studs that failed UT inspection, and repaired broken key block screw holes.  Various minor repairs were performed on damaged center pins, damaged axial tongue fits, damaged key pockets and locating pin slots, and damaged bell seal bores.

The remaining installed nozzle chambers horizontal and vertical face fretting damage and nozzle partitions were repaired, along with admission-side impact damage, all followed by wall thickness UT inspections and evaluation.  The repaired and restored B2 nozzle chamber was then reinstalled into the casing and a new top hat and all-new flex plates welded into location.  Final heat treatment, machining, and NDE inspections were performed without issue.

Upper half work included various minor repairs on damaged center pins, damaged axial tongue fits, damaged key pockets and locating pin slots, and damaged bell seal bores.  The remaining installed nozzle chambers horizontal and vertical face fretting damage and nozzle partitions were repaired, along with admission-side impact damage, also followed by wall thickness UT inspections and evaluation. The repaired and restored C3 nozzle chamber was then reinstalled into the casing and a new top hat and all-new flex plates welded into location.  Final heat treatments, machining, and NDE inspections were performed without issue.

Once the two nozzle chambers’ reinstallations were completed, new nozzle plate seals were installed and machined, and new bell seals were supplied, final machined, and fit checked to each inlet snout bore.

Upper Half Casing Nozzle Chambers Flex Plates Welding & Inspections Completed

Center Flow Guide

Center flow guide work included horizontal joint stud UT inspection, welding and machining of the axial and vertical key fits, centering-slot damage repair, removal and replacement of lower-half vertical keys, and final assembly fit checks to the inner casings.

Final Assembly Verification and Shipment

MD&A then performed and verified final assembly checks of the center flow guides into the casing halves and performed a final upper half casing “tops-on” check to ensure closure of the horizontal joint and all nozzle chamber positions and clearances were acceptable.

All components were completed and returned to the site six days ahead of the contract schedule.

Because of our vast knowledge and experience with different types of OEMs, MD&A experts can perform any welding repairs. Our commitment to excellence has earned customer trust for all turbine-generator needs. We focus on delivering consistent quality and value with fast response, superior communications, and innovative solutions. We are your full-service, OEM-alternative!

Have MD&A look at your casings today, call our Turbine-Generator Repair Facility at (314) 880-3000, or use our Contact form.

Final Assembly Checks and Preparation for Shipment

Final Assembly Checks and Preparation for Shipment