COATING TECHNOLOGIES FOR BOILERS IN

POWER PLANTSSRINIVASAN SHANKAR- SHANKAR ASSOCIATES

BoilersSuper heaters

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF

BOILERS

BACKGROUND• Increase in demand for energy leads to higher operating temperature and

more demanding operating conditions in boilers

• As a result higher erosion/corrosion rates of metallic components of

boilers for plant is being observed

SOLUTION• Coating technologies are flexible solutions to protect the

different zones of the plant with the most cost-effective

approach

Coating tree

On site

During manufacturing

Erosion resistance

Boiler

High temperature

(< 450 °C)

Very High temperature

(>450°C)

Erosion

(Blowers)

Superheaters Grid

Water jackets

Themocouple pits

Ancillary components

Boilers

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF

BOILERS

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF

BOILERS

Super heater (during

manufacturing)

Thermocouple pits

Metallurgical bonding

Low dilution (< 2%)

Advanced materials available

Laser welding

Boiler (on-site and during

manufacturing)

Super heater (during

manufacturing)

Water jackets

High Thickness (>2mm)

Metallurgical bondingArc welding

Boiler (on-site and during

manufacturing)

Superheater (no bending)

High deposition rate

Suitable for on-site applications

Large selection of material

available

Thermal spray

COATING TECHNOLOGIES

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF

BOILERS

Blowers

Super heater

Grid components (Fluidized

bed)

•For specific applications

•Not weldableHard material•CrC – NiCr

•Stellite 6

Super heater (during

manufacturing)

Thermocouple pits

•Advanced materials

•Resistance at higher

temperature (compared to

IN625)

•Difficult to weld

Co-Cr-Ni-Al

Boiler (on-site and during

manufacturing)

Super heater (during

manufacturing) T <450 °C

•Standard, proven materials

•Large reference lists

•Easy-to-weld material

Ni-Cr-Mo•IN 625

•Hastelloy

MATERIAL SELECTION

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF

BOILERS

THERMAL SPRAY

• Two processes: HVOF and Wire Spray

• Flexible technologies easy to transfer on-site

• Large selection of applicable materials

• “Cold”, robust application process

• High productivity, both automatic and manual

• Lower cost

THERMAL SPRAY

TECHNOLOGIES FOR CORROSION

PROTECTION OF BOILERS

THERMAL SPRAY• The intrinsic limit of thermal spray coatings is the

residual porosity of the deposited layer.

IMPROVING STRATEGIES

• Porosity reduction through technology development

(HVOF vs. Wire Spray)

• Porosity sealing

TS Processes: a comparisonTS Processes: a comparison

0

1000

2000

3000

4000

0 200 400 600

Velocity (m/s)

Tem

pera

ture

(C

°)

arc

flame

VPS

HP/

HVOF

APS

Wire SprayWire Spray

HP/HVOFHP/HVOF20 lbs/hr (5 kg/hr)

Powder InputKerosene

Oxygen

Water

Cooling

Water

Cooling

Particle

3300-3900 FPS

(1000-1200 m/s)

Gas

1800-2000 m/s

3100 K

(a.u

.) Temperature

Velocity

Pressure

Chamber

Nozzle

Barrel

3100 K

2500 K

1800 m/s

1 MPa

0.13 MPa

Zone of powder

injection

TS Processes: a comparisonTS Processes: a comparison

• Not suitable for manual operation

• More complex to install on site

• More expensive

• Higher porosity• Lower bond strength

Limitations

• Better bond strength• Very low porosity

• Low running cost• High productivity• High thickness• Easy operation on

site• Suitable for manual

operation

Advantages

>7010-30 Tensile bond strength (MPa)

< 15 to 10Coating porosity (%)

28002500Gas stream temperature (°C)

400-700120-200Particles velocity ( m/s )At the impact

>2000450Gas stream velocity ( m/s )

HP/HVOFWire FlameThermal spray process

TS Processes: a comparisonTS Processes: a comparisonMicrostructure of as coated material Microstructure of as coated material –– IN625IN625

High Pressure Wire Spray HVOF

TS Processes: a comparisonTS Processes: a comparisonMicrostructure after exposure in boilerMicrostructure after exposure in boiler

A) WIRE SPRAY IN 625A) WIRE SPRAY IN 625

At 400 °C – 1000 h At 500 °C – 1000 h

TS Processes: a comparisonTS Processes: a comparisonMicrostructure after exposure in boilerMicrostructure after exposure in boiler

B) HVOF IN 625B) HVOF IN 625

At 400 °C – 1000 h At 600 °C – 1000 h

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

SealSeal WWWW

• IN625 layer deposited

with High pressure wire

spray

• High temperature sealing

with ceramic aluminum

slurry (sacrificial layer)

• Max. metal temp.: 300 °C

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

SEAL WW

• High Pressure wire spray is a proven technology able toproduce reproducible coatingsalso in harsh condition

• Slurry sealing is fast, unexpensive and can bereapplied at each plant stop

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

SEAL WW APPLICATIONS

Flameseal WW has been applied on waterwalls of power plant boilrs

• More than 5000 m2 in exercise

• 150 – 1500 ton/day

• Tsteam : 240 – 280 °C

• Tfumes : 700 – 950 °C

• Metal waste (uncoated): 0.3 – 0.7 mm/y

• Metal waste (coated): < 50 µm/y

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

Uncoated pipes Seal WW Coated pipes

-3

-2,5

-2

-1,5

-1

-0,5

0

0,5

1

0 2 4 6

Operating years

Thic

kness losses

(m

m)

Corrosion of tubes

protected with

Flameseal

Corrosion of

uncoated tubes

-3

-2,5

-2

-1,5

-1

-0,5

0

0,5

1

0 2 4 6

Operating years

Thic

kness losses

(m

m)

Corrosion of tubes

protected with

Flameseal

Corrosion of

uncoated tubes

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

Micrographic examination of a

scale of coating extracted after 4

years of service in a Municipal

waste boiler operating at 30 bar.

No corrosion in the IN 625

layer

Limited corrosion growth at

the interface

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

AlloyAlloy HH

• Corrosion resistant layer

deposited with HVOF

• Large selection of material

applicable

• No sealing required

• Max. metal temp.: 400 °C

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

ALLOY H

• HVOF produces thermal spray coatings of superior quality

• With optimized equipment can beapplied on very large surfaces as, forexamples, on boiler panels prior toassembly of the boiler

• It is also possible to install on site HVOF equipment, if boiler dimensions are large enough

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

Super heater (in blower area)

Grid components

•For specific applications

•As overlay coating on Alloy

H525

Hard material•CrC – NiCr

•Stellite 6

Boiler panels for high S fuel

Power plant boilers

• Composition similar to

Hastelloy C276

•Ni-Cr 50-50

Alloy H 555

Alloy H5050

Boiler panels

Water jackets

• Composition similar to IN 625Alloy H 525

Alloy H Applications

THERMAL SPRAY TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

• 320 MW ENEL boilers for use with S-

containing fuels (i.e. ori-mulsion) and

reducing combustion conditions

• No thickness losses after 5 years

operations

ALLOY H5050 APPLICATIONS

CLADDING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

CLAD

• Clad is a family of coating produced by arc cladding

• Proven technology possible to transfer on-site

• Metallurgical bonding

• Standardized process, widely accepted by the

industry

• Possible both automatic and manual application

• Temperature resistance up to 400-450 °C

CLADDING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

• A large reference list of CLADapplications is available, mainlyusing IN 625 alloy; CLAD hasbeen applied both in boilers and in superheaters

• Application costs can be reducedplanning the cladding during the construction of the components

CLAD APPLICATIONS

CLADDING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

Clad Coated Panel

area in boiler :

•Tsteam: 250 °C

•Tfumes: 1020 °C

Position: at the end of

the postcombustion

(Picture taken after 2 years in

service)

CLADDING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

APPLICATIONS

Clad has been applied on superheater and boilers:

• 150 – 1500 ton/day

• Tsteam : 350 – 450 °C

• Tfumes : 700 – 950 °C

• Metal waste (uncoated): 1 – 3 mm/y

• Metal waste (coated): < 0.1 – 0.3 mm/y

CLADDING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

Corrosion phoenomena

on clad IN625:

Superheater tube

operating at metal

temperature of 520 °C

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

Micrographic examination of a 2-

layers coating composed by:

•1 mm Clad

•0.5 mm Seal

after 1000 h corrosion test @ 500°C

No corrosion at the

interface of the two layers

No corrosion growth at the

interface with base metal

Large selection of materials available as top coat !

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

EROSION PROTECTION OF BLOWERS AND BURNERS AREA

Flam H 834 is the result of exhaustive research in which chemical composition and coating

process are optimised to reach maximum microhardness values.

This process is suitable for pieces subject to severe high temperature erosion. Blowers of

coal burning power plants are coated with Flam H 834

CHEMICAL COMPOSITION

Chrome Carbide (Cr3C2) 75%

Nichel Chrome 25%

TECHNICAL PROPERTIES

Excellent erosion resistance

Excellent corrosion resistance at high

temperature

PHYSICAL PROPERTIES

Microhardness (HV 300) 800÷÷÷÷1000 HV

Porosity < 1%

Bond strength > 60 Mpa

LASER TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

LasercladLaserclad

• Advanced alloy layer deposited

with laser cladding technology,

developed by CESI

• Low dilution – fine microstructure

– metallurgical bonding

• Suitable for superheaters and

critical parts of boilers

Ni-Cr-Co alloy laser cladding on

thermocouple sheaths of incinerators for

high temperature operation

Laser cladding of Co-Cr-Ni alloy (28%-29%-bal.) on thermocouple

sheaths: sheath diam. 22 mm; coated length 550 mm; two layers

laser cladding; cladding average thickness 1.5 mm

LASER TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

Superheater bundlemanufactured withLaserclad tubes

Thermocouple pits

coated with Laserclad

LASER TECHNOLOGIES FOR CORROSION

PROTECTION OF BOILERS

Transition between

coated and

uncoated area in a

superheater tube

(after 6 months):

•Tsteam: 350 °C

•Tfumes: 1020 °C

COATING TECHNOLOGIES FOR

CORROSION PROTECTION OF BOILERS

COATING TECHNOLOGIES - SUMMARY

Boilers (on site and

manufacturing)

SH

1.2 m2/shift2450Clad

Boilers

(manufacturing)

SH (no bending)

8 m2/shift0.4350 -

400Alloy H

Boilers

Optimal on site

10 m2/shift0.5300 Seal WW

ApplicationsNominal

Productivity

(for one torch)

Thickness

(mm)

Max. T

( °C)

Technology