Degradation modes

HRSG Operation & Inspection Seminar 2011

Barcelona, 27Sep 2011

Schoonmaker / Decoussemaeker / Matukonis

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 2

Degradation Modes

• Fatigue:- Thick walled components with high temperatures /

temperature gradients• HP drums• HPSH and RHTR outlet manifolds (fast delta t at start)

- Specific locations subject to temperature differentials

- Specific locations subject to quench during start-up, shut

down or low load operation (desuperheater)

• Creep:- HPSH and RHTR outlet

manifolds and harps

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 3

Degradation ModesWater side corrosion

• Evaporator, drums, economiser (water filled):(or in superheater during shut down when water accumulates)- Pitting (pits can lead to cracks): attack by oxygen- Under deposit corrosion (deposits (e.g. evap) and contaminants)

• E.g chloride from condensor (leads to hydrogen damage) or phosphate from dosing or NaOH from dosing or resin regeneration

(leads to caustic gauging)

• Flow accelerated corrosion:- Protective magnetite layer dissolves into flowing water (single

phase) or wet steam (two phase)• Corrosion fatigue cracking at tube attachments or restraints (areas of

stress concentrations, not high enough to cause damage, but in combination with corrosion …):- Stress damages inner layer (magnetite), exposing it to corrosion -

> small corrosion filled cracks

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 4

Degradation ModesWater side corrosion

Oxygen pitting Corrosion Fatigue

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 5

Degradation ModesWater side corrosion: FAC

• Main affected locations:• Economizer: tube to header, nozzles at headers, tube bends• LP system: tube to header, elbows, downcomer at drum• Deaerators

FAC damage at LP evaporator tube to header connection

LP drum water separator can: hole enlargement

(early indicator)

Deaerator loss of magnetite

Economizer with magnetite loss and material thinning

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 6

Degradation ModesGas / atmospheric side corrosion

• Gas side dew point corrosion or general stand still corrosion- Cooling of acidic flue gas or condensate or ambient

humidity

Pressure drop and reduced heat transfer

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 7

Degradation ModesOverload

• Freezing• Overheating:

- Long term:

Material choice over the limit, caused by design, scaling,

blockage, … (at highest temp. location)- Short term:

Start up, firing

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 8

Degradation ModesWelding problems

• Dissimilar metal welds

• Skill issues or lack of following of the procedure- Combined with lack of QC

www.alstom.com/power

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 10

HRSG Field IssuesFlow accelerated corrosion (FAC)

• What is FAC?- Protective magnetite layer dissolves into flowing water

(single phase) or wet steam (two phase)

- Conditions to get FAC:• Temperature between 80°C and 230ºC• Turbulence• Carbon steel• Water chemistry (Low pH)

Typical scalloped surface Economizer tube bends at inlet header

Hole on top of LP evap header(blue: thinned material)

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 11

HRSG Field Issues

• FAC control:• Inspection and NDE in critical areas• Water chemistry:

- Control pH (high enough) and oxygen (not zero)

• Upgrade from carbon steel to material with Cr (1 to 2%)

IP evaporator harp header Header replacement

© ALSTOM 2011. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation Title - Presenters Initials - dd mmm yyyy - P 12

HRSG Field Issues

• Case Study: Replacement LP evaporator headers

• Staggered design for improved accessibility for the welding

• Boroscopic Inspection Points for examination of the weld roots

• Header tube stubs are constructed from 2¼% Cr, to increase the header resistance to FAC.

• Use of phased array for 100% volumetric inspection of all full penetration welds

• Reduction of required outage time from 50 days to below 30 days

Improved design and reduced outage time