# Presentation: 435890

## Fireside and Steamside Corrosion of Alloys for USC Plants

***K. Natesan and J. -H. Park***
***20th Annual Conference on Fossil Energy Materials, Knoxville, TN, June 12-14, 2006***
***Work supported by DOE/Office of Fossil Energy, Advanced Research Materials Program***

## Outline		

**   ****Background**
**   ****Objectives****	****	**
**   ****Materials and experimental procedure**
**   ****Performance of Fe-base alloys**
**   ****Performance of Ni-base alloys **
**   ****Project summary**

## Efficiency and Emissions for Coal-fired Boiler Technologies

## Pulverized Coal-Fired Boilers

**Goal is to develop ****advanced**** steam cycles**

**Current:   16.5-24 MPa (2,400-3,500 psig), 540°C (1000°F) steam**
**Near-Term Goal:    34.5 MPa (5,000 psig), 650°C steam**
**Long-Term Goal:   34.5 MPa (5,000 psig), 760°C steam**

**Waterwall corrosion:****	****    Formation of pyrosulfates, trisulfates**
**Superheater corrosion:   Formation of alkali-iron trisulfates****	****	****	****    Alkali sulfates/alkali chlorides induced****                                           corrosion    ****	****	****	****    Loss of mechanical properties**

## ANL Program Objectives

**Evaluate fireside corrosion performance of metallic materials in coal-ash environments typical of advanced steam cycle systems**
**Evaluate the role of alkali sulfates and alkali chloride in the corrosion process**
**Establish the relative corrosion performance of off-the shelf and experimental alloys**
**Surface engineering of alloys to improve fireside and steamside corrosion resistance**

## Fe-base Alloys for use up to 650°C

## Fe-base Alloys for T up to 700°C

## Nickel-base Alloys for use at T up to 760°C

## Deposit Chemistry

**(a)****	****SiO****2 ****: Al****2****O****3**** : Fe****2****O****3**** = 1:1:1**
**(b)****	****Na****2****SO****4**** : K****2****SO****4**** = 1:1**
**(c) ****	****NaCl**
**Ash 1:  90 wt.% (a)  + 10 wt.% (b)**
**Ash 2:  85 wt.% (a)  + 10 wt.% (b) + 5 wt.% (c)**
**Ash 3:  89 wt.% (a)  + 10 wt.% (b) + 1 wt.% (c) ****	****	****	**

## Corrosion Test Facility

## Facility for Corrosion Test in the Presence of NaCl Vapor

## Steam Exposure Test Facility

**Water pump**

**Furnace**

**Water source**

**Controller**

**Steam condenser**

**T recorder**

**Alumina chamber**

## Corrosion Loss in Coal Ash + Alkali Sulfate

## Corrosion Loss in Coal Ash + Alkali Sulfate + NaCl

## Effect of NaCl on Corrosion

## Effect of Deposit Chemistry on Corrosion of Fe-base Alloys

## Effect of Deposit Chemistry on Corrosion of Ni-base Alloys

## Comparison of Corrosion Rates for Fe- and Ni-base Alloys

## Corrosion Morphology in Alloy 800 Clad with 671

**900 h at 650°C in ash + sulfates+1%NaCl**

**800**

**671**

## Exposure Conditions: 1680 h, 650°C, Ash + sulfates

**10 μm**

***Alloy 625***

**20 μm**

**20 μm**

***Alloy 602CA***

## Alloy 230

***Alloy 230***

**20 μm**

***Alloy 45TM***

**10 μm**

**20 μm**

## Hot Corrosion of Ni-Cr Alloys

## Specimens after 100-h Exposure in Air +1 % SO2 + 300 vppm NaCl

**Mod. ****9Cr-1Mo**

**Mod. ****9Cr-1Mo**

**NF616**

**HCM12A**

**HCM12A**

**E911**

**E911**

**NF616**

## Effect of Exposure Environment on Corrosion

## Cross section of E911 specimen after 100-h Exposure in Air +1 % SO2 + 300 vppm NaCl

## Schematic of Morphology in Ferritic Alloys Exposed in Air +1 % SO2 + 300 vppm NaCl

**Air + 1%SO****2**** +****NaCl vapor**

**Fe Chloride**

**Fe Oxide**

## Coated Specimens after 200-h Exposure in Air +1 % SO2 + 300 vppm NaCl

**Mod. ****9Cr-1Mo**

**Mod. ****9Cr-1Mo**

**NF616**

**HCM12A**

**HCM12A**

**E911**

**E911**

**NF616**

## Cross section of coated-E911 specimen after 200-h Exposure in Air +1 % SO2 + 300 vppm NaCl

## Oxidation in Steam at 725°C

**HR3C**

**347HFG**

**Modified 800**

**SAVE25**

## Scaling and Penetration in Steam at 725°C

**HR3C**

**SAVE 25**

**347HFG**

**Modified**** ****800**

## Oxidation Rate in Steam at 725°C

## Project Summary

**   ****Fireside corrosion is a major issue in selection of materials for advanced steam cycles**
**   ****We have conducted studies at ANL to evaluate the corrosion performance of several Fe- and Ni-base alloys **
**   ****The laboratory tests simulated the combustion atmosphere and three deposit chemistries which included ash constituents, alkali sulfates, and two levels of NaCl**
**   ****Corrosion rates exhibited a bell shaped curve (for Fe base alloys) with peak rates around 725°C, and the rate itself is dependent on the alloy chemistry**

## Summary (continued)

**   ****Several Fe-base alloys showed acceptable rates in the sulfate containing coal-ash environment; but, NaCl in the deposit led to catastrophic corrosion at 650 and 800°C**
**   ****Ni-base alloys, tested for 1680 h at 650°C, showed a local attack in the form of pits and associated sulfidation of the alloy.  This form of attack is well established and is known as “low temperature hot corrosion” or Type II hot corrosion**
**   ****Surface modification (including coatings) is a promising option to decrease the corrosion rate and wastage in ferritic alloys**
**   ****Need to establish the maximum levels for alkali sulfates and alkali chlorides in combustion environment (and their relationship to coal feedstock) for acceptable corrosion**