Lay-up Protection for Boilers and HRSGs - American Public Power ...

Lay-up Protection for Boilers 

and HRSGs 

APPA E&O Conference 

APRIL 2005 

1

FOR SALE: 250 MW 2-on-1 Natural Gas Fired 

Combined Cycle Plant 

Completed in 2000, lightly used, left full of water 

with no lay-up or preservation. 

Make Offer 

2

Goals of Proper Lay-up 

• Minimize Downtime 

Corrosion 

• Eliminate Corrosion Product 

Transport on Startup 

• Reach Chemical Operating 

Limits Quickly 

3

Lay-up the Entire Steam 

Cycle! 

Vent 

HP Turbine 

IP 

Turbine 

LP 

Turbine 

Condenser 

Deaerator 

Vent 

Boiler 

HP 

Heaters 

LP 

Heaters 

Condensate 

Polisher 

4

Lay-up is Critical for HRSG’s 

• Cycle frequently 

• Faster heating cycles 

• Complex circulation 

• Often stand-alone (no source of aux. 

steam) 

• Chemical cleaning more complicated 

5

Your Choice 

Rust and Corrosion 

6

Your Choice 

Passivation and Protection 

7

Failure Mechanisms Affected 

by Poor Lay-up 

• Oxygen Pitting 

• Corrosion Fatigue 

• Under Deposit Corrosion 

– Hydrogen Damage 

– Caustic Gouging 

8

Oxygen Pitting 

Causes: 

• Downtime Oxygen 

• Dissolved oxygen on 

Startup 

• Corrosion Products 

Location: 

• Anywhere where water 

and oxygen coexist 

9


• Starts with a deposit 

• Driven by oxygen in the water/air versus 

no oxygen under the deposit 

• Heating increases corrosion rate 

• Chloride increases corrosion rate 

10

Normal Passivation 

Half Reactions 

Fe → Fe +2 + 2e - 1 / 2 O 2 + H 2 O + 2 e - → 2 OH - 

Fe +2 + 2 OH - Fe (OH) 2 

2 Fe(OH) 2 + O 2 Fe 2 O 3 + H 2 O (300 F) 

Fe 0 2e - 

Fe 2 O 3 

O 2 OH - 

Fe +2 Fe(OH) 2 Fe 3 O 4 

Anode 

Steel 

Cathode 

11

Normal Passivation 

Random anodic and cathodic sites create a passivation layer 

AC 

AC 

AC 

Fe 0 

AC 

AC 

2e - 

AC 

AC 

AC 

AC 

AC AC AC 

AC AC 

AC 

AC 

AC 

AC 

AC 

AC 

AC 

A- Anode C- Cathode 

Steel 

12


Deposits create a localized cathode and anode 

that form a corrosion pit 

High dissolved oxygen 

Fe O 2 OH - 

2 O Oxygen-deficient area 

3 

Fe(OH) 2 

Anode 

Steel 

Cathode 

13

Corrosion Fatigue 

1. Stress cracks protective oxide 

2. Oxygen pits form 

Fixed point 

14

Corrosion Fatigue 

Causes: 

• Oxygen plus Stress 

• DO on startup 

Affects: 

• LP Economizer and 

Evaporator 

• Fixed points, headers 

15

Under-deposit Corrosion 

Steam out 

Conc. chemicals 

Heat 

Boiler water in 

16

Underdeposit Corrosion 

Causes: 

• Deposits 

• High heat flux 

• Improper Chemistry 

17

Lay-up Considerations 

Not Time Dependent 

Good Lay-up must work 

for a day or a year 

18


Quick return 

OR 

Scheduled return 

19


Breech 

OR 

No Breech 

20

Corrosion Triangle 

21

Dry Lay-up — Exclude Water 

22

Wet Lay-up — Excludes Oxygen 

23

Lay-up Options 

• Dry Lay-up 

– Hot Drain 

– Dehumidified Air 

– Desiccants 

• Wet Lay-up 

– Nitrogen 

–Steam 

24

Design Issues Affecting Layup 

• Can all headers and piping be drained 

completely 

• How quickly can it be done 

• How accessible are drain valves 

25

Design issues: headers 

Cannot be drained : Wet Lay-up only 

Dry Lay-up will work 

26

Dry Lay-up 

Advantages 

• Only option when repairs are required 

• Requires less time and cost to 

maintain 

27


Disadvantages 

• Need to get systems dry and keep 

them dry 

• Requires considerable time and water 

on startup 

28

Steps for Dry Lay-up 

• Drain HRSG hot (some drain 

under nitrogen pressure) 

• Drain out associated feedwater 

equipment and piping 

• Drain and dry out condenser 

• Make sure ALL drains are opened, 

including header drains 

29

Maintaining Dry Lay-up 

• Use continuous dehumidified air 

circulation 

OR 

• Close drains/drums and use desiccant 

30

Dehumidified Air 

• Air must circulate though all equipment 

• High flows to achieve dew point of – 10F 

as quickly as possible 

• Continue to circulate 1% system volume 

per hour 

31

Silica Gel 

• Use 5 lbs. silica gel/100 ft 3 of panel volume 

• Place in each accessible drum 

• Use indicating type 

• Check regularly 

– At least twice during first week 

– Once per week for first month 

– Once per month thereafter 

32

Vapor Phase Inhibitors 

• Used on clean metal surfaces 

• Addition rate- ~3 lbs per 1000 gallons 

capacity 

33

Vapor Phase Inhibitors 

• Volatile at ambient temperatures 

• Destroyed in steam blow or operation 

• Treatment can be repeated if needed 

34

VPI Preservation 

After 30 days 

After 106 days 

35

Wet Lay-up 

Advantages 

• Quick restart 

• Minimizes corrosion product transport 

36


Disadvantages 

• Requires freeze protection 

• More time and cost to maintain properly 

37


Hot 

or 

Cold 

•Uses Auxiliary 

Steam 

• Reduces Thermal 

Cycling Stresses 

•Faster Starts 

• Nitrogen 

•Simple to maintain 

•No fuel costs 

38

Nitrogen Cap 

Cap should be applied to: 

• Steam Drum(s) 

• Deaerator (if separate) 

• Condenser 

39

Danger:Nitrogen 

• Nitrogen lay-up is designed to prevent 

oxygen from entering the boiler 

• Nitrogen will NOT support life 

• All confined spaces MUST be clearly 

marked 

• Confined Space Entry Procedures 

MUST be followed 

40

Nitrogen Addition Points 

Vent 

HP Turbine 

IP 

Turbine 

LP 

Turbine 

Condenser 

Deaerator 

Vent 

Boiler 

HP 

Heaters 

LP 

Heaters 

41

LP SH 

IP SH 

DA 

LP Drum 

Feedwater Preheater 

From HP FW Pump 

42 

HP Economizer 

IP Economizer 

HP Economizer 

LP Evaporator 

IP Drum 

To IP Turbine 

To LP Turbine 

HP Evaporator 

HP Econmizer 

IP Evaporator 

HP Drum 

--Nitrogen Addition Points 

Drain 

Drain 

To HP Turbine 

HP SH

Nitrogen Cap- Drums 

• Enters the drum through 

connection on vent line 

• Nitrogen feed started while drum 

is still hot (~212°F) 

• Less than 5 psig of pressure is 

applied 

43

Nitrogen Cap - Condenser 

• Addition starts while while steam 

turbine is still spinning down 

• Added quickly at first, then slowly 

as the vacuum approaches zero 

• Constant flow of 20 SCFH is 

maintained while the unit is down 

44

Wet Chemical Lay-up 

• pH of water 9.8 with ammonia or 

amines 

• Hydrazine or other scavenger may be 

added 

• Need to circulate and test 

45

LP SH 

IP SH 

DA 

LP Drum 

Feedwater Preheater 

From HP FW Pump 

46 

HP Economizer 

IP Economizer 

HP Economizer 

LP Evaporator 

IP Drum 

To IP Turbine 

To LP Turbine 

HP Evaporator 

HP Econmizer 

IP Evaporator 

HP Drum 

--Nitrogen Addition Points 

--Chemical Sampling Points 

Drain 

Drain 

To HP Turbine 

HP SH

Wet Chemical Lay-up 

• Requires significant amounts of chemical 

• Must add nitrogen or steam provide adequate 

protection above the water line 

• May create an environmental issue if you 

have to drain the HRSG (particularly if 

hydrazine is used) 

47

Transitions 

Dry To Wet 

• Need a source of deoxygenated water 

• Add chemical treatment during fill 

• Cap with Nitrogen 

48

Transitions 

Wet to Dry (Cold) 

• Drain under nitrogen pressure 

• Continue to blow nitrogen until water is 

gone 

• Dry out with dehumidified air 

• Use dry air or silica gel to maintain 

49

Transitions 

Wet to Dry (Better) 

• Fire boiler to 25 psig 

• Drain under nitrogen pressure 

• Dry out with dehumidified air 

• Use dry air or silica gel to maintain 

50

Startup Chemistry 


Boiler/HRSG fill-water should be: 

•Hot 

• Deaerated 

• Chemically Treated 

51

• Feedwater 


Treatments 

–Amine 

– Scavenger 

• Boiler 

– Phosphate 

– Caustic (if needed) 

52


Wet Lay-up (Nitrogen) 

• Chemistry from the lay-up predominates 

• Treat with a heavier than normal dose 

of amine and scavenger to account for 

high make-up rates 

53

Reference Document 

ASME CRTD-Vol. 66 

Consensus for the Lay-up of Boilers, 

Turbines, Turbine Condensers and 

Auxiliary Equipment 

Available at the www.asme.org 

54

Lay-up Protection for Boilers and HRSGs - American Public Power ...

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