Engineering Analysis of Furnace Stave with ANSYS Metal Stave Analysis ANSYS...Engineering Analysis...

Engineering Analysis of Furnace Stave with ANSYSPatented UltraLife® Stave

Property of Berry Metal Company – Confidential and Proprietary

Stave Analysis Presenters

• Ed Green, P.E.

• Principal Engineer

• BS Pitt

• 30+ years Design &

Manufacturing

• Learned FEA at Pitt on paper

computer terminal

• Danyang Li

• Engineering Analyst

• MS Engineering Carnegie Mellon

• Working on MS Computer

Science Georgia Tech

• Engineering Tsinghua University

(Top engineering university in

China)

• 7 years Design & Analysis

About the Company

• Over 65 years of experience

• Experience in EAF, BOF and

Blast Furnaces – Iron and

Steel Industry

• ISO 9001:2008 Certified

• Over 75 Patents, several

Pending

• Locations (Pittsburgh &

Greater Chicago Area)

• Equipment Engineering and

Manufacturing Company

• OEM Supplier of Components

• On-Site Technical Support

• Continuous Product

Improvements

Engineering Capabilities

Full Service Engineering Department

– 2D & 3D Software

– Finite Element Analysis (FEA) Software

– Computational Fluid Dynamics (CFD) Software

– Basic Engineering & Detailed Engineering

– Scope & Specification Development

– Custom Equipment Design

• This project was to support a bid proposal.

• Customer had blast furnace staves that were

failing after 15 years and was looking to

replace two rows.

• Analyze the customers incumbent staves

using ANSYS and determined why they failed

• Identified other potential failure points

• Show by analysis why Berry Metal Ultra-Life

staves would not fail in the same way

Project Description

Background of the Problem

Blast Furnace Background

Blast Furnace Stave Design

Water Cooled

Stave LiningWater Cooled

Stave Lining

Blast Furnace

Converts iron ore to

iron

1,800 to 2,000°C

Water Cooled Copper Stave

Lined Wall in Blast Furnace

What is a Typical

Furnace Stave?

Cooling Water Out

Cooling Water Outlet

Bolts

Pin

Bolts

Refractory

Stave

Panel

Stave is a water-cooled panel of a blast furnace made of copper.

It’s mounted on the inside of the steel shell and may experience

extreme thermal condition due to high furnace temperatures.

Refractory is mounted on the hot side to reduce the

temperatures the stave is exposed to.

Typical Stave Failure

Mechanisms

Deflection

Pipe Weld Cracks Due to Thermal

Expansion

Pipe Weld Cracks Due to Flow Disruptions

• Plug Washing

• Face Washing

• Bolts Break

• Cyclic stresses due to rapid heat up and cool down

• Thermal expansion causing stave deflection

• Non uniform water flow

• Lost Accretion/Water leaksWeld or

Pipe

Fracture

Cyclic

Stress

Pipe

Bending

Accretion

And

Refractory

Loss

Crack Propagation


Mechanisms

Stave

Thermal

Growth

Grout

Furnace

Wall

Can Resists Sideways Movement

Preventing Pipe Side Movement

Bellows Allows In &

Out Movement


Mechanisms


Mechanisms

BOSH STAVE – Top is worn smooth,

Bottom has near full rib depthSTACK STAVE – Top has ribs.

Bottom worn smooth

Face washing from loss of refractory

BLAST FURNACE –

Refractory worn away

• Water pipe weld failures

• Mounting bolt failures

• Staves buckled from deflection

• Abrasion on Hot Face

• Desired Stave Life is >20 years

Typical Staves at End of Life


Mechanisms

New Design BMC Ultra-Life Stave

BMC Ultra-Life Stave

• Patented cast in copper alloy pipe

– More efficient water cooling across stave

– Removes Pipe Stress

– Reduces Bolt Stress

– Reduces Stave Deflection

Patented Technology

Furnace Cooling System

Ultra-Life Stave

Intertwined passages

UltraLife®Vertical Drilled

Passages

VERSUS

Patented Technology

Ultra-Life Stave

Simulation

Simulation

Analysis Work Flow

body temperature

SpaceClaimMesh for

CFDCFX

Linear Material Static Structure

Linear Material Properties

Non Linear-Static Structure

Material Property

Non-linear Material

Properties

body temperature

SpaceClaim

SpaceClaim

Stave Geometry

Conventional Stave

Copper plate with

drilled passageways and

copper pipes welded to plate

BMC Ultra-Life Stave

Cast copper plate with

Copper alloy pipe inside casting

Water Outlet

Water Inlet

Water Inlet

Water Outlet

Bolt

Bolt

Bolt

Bolt

Bolt

Bolt

Bolt

Pin

Pin

Bolt

Copper plates

36” x 120” x 6” thick

Model Preparation in

SpaceClaim

• Model made in Inventor, imported to ANSYS in .stp format

• Steps to refine the model:• Name surface groups in SpaceClaim – CFX will not recognize

surfaces named in Mesh

• Careful to turn off parts that are not being modified, tend to join

together during non-related modifications

• Delete any unnecessary fillets, holes or other features to simplify the

model.

• Split model body to create sweepable bodies.

• E.g.: The teeth on the stave

• Use Repair tool to make sure the model geometry is OK


SpaceClaim

Share Topology to Align Nodes and Elements While Meshing

CFD Mesh


CFD Meshing

Model Mesh

• Set mesh preference to CFD and solver preference to CFX.

• Declare solid and fluid domains.

• Use Brick elements to greatest extent possible – Tets can easily

have 10M elements or nodes, Bricks can be closer to 2M to 3M

elements & nodes

• Inflation Layers applied in fluid domains for better fluid boundary

layer simulation

• Sweep method applied to all sweepable bodies

• Applied Hex Dominant body wherever is possible apart from

sweepable bodies.

Model Mesh – Stave Body

Sweep method

Sweep method

Hex Dominant

method

Model Mesh – Quality Check

Aspect Ratio: < 50

Skewness: 0-0.25 (excellent), 0.25-0.50 (very good), 0.50-0.80 (good), 0.80-0.94 (acceptable), 0.95-0.97 (bad), 0.98-1.00 (unacceptable).

Orthogonal quality: 0-0.001 (unacceptable), 0.001-0.14 (bad), 0.15-0.20 (acceptable), 0.20-0.69 (good), 0.70-0.95 (very good), 0.95-1.00 (excellent)

Model Mesh – Water Volume

Sweep

method

Inflation Layer• Use edge sizing one end

• Inflation – geometry pick

face, Boundary pick edge

• Sweep body

CFX

CFX

CFX Setup

Setup Domains for each Material and each Fluid Volume

Setup Boundary Conditions such as Heat Flux & Water Mass Flow

CFX Setup

Heat Flux: 50-500 kW/m2

Heat Transfer Coefficient:

Back Face

100 W/K-m2 @400F

Small gap between stave and

grout, low heat transfer – less than .1°F at high heat flux

condition

4 x Water Inlet

4 x Water Outlet

• Heat Flux Load

– 500 kW/m2 is industry practice for assumed maximum

value of heat load when all refractory is lost.

– 60 kW/m2 is calculated from customers provided data. Water temperature rise across a stave is 5.4°F, water

flow in gpm is known. Using formula

𝑘𝑊 =𝑔𝑝𝑚

𝑔𝑎𝑙𝑚𝑖𝑛

𝑥 8.35𝑙𝑏𝑠𝑔𝑎𝑙

𝑥 60𝑚𝑖𝑛ℎ𝑟

𝑥 1𝐵𝑡𝑢𝑙𝑏 𝐹

𝑥 ∆𝑡 𝐹

3412

𝐵𝑡𝑢ℎ𝑟𝑘𝑊

– Heat Flux = kW/projected surface area of stave face

CFX Setup

CFX Setup

• Named surfaces are important! The same name as in the

SpaceClaim Groups. Useful for setting up Domains and Boundary

Conditions

• The surfaces will auto pop-up in the drop-down list for convenience

When a model has multiple fluid volumes need to make separate

domain for each volume. Can’t combine into one because Inlets &

Outlets get confused

CFX Solver

• Multi-core parallel solver is used for higher efficiency

CFX Results Comparison

CFX Results Comparison

Incumbent BMC Ultra-LifeTemperature Front Side

Heat Load 500 kW/m2

No refractory

Ave 409°FAve 527°F

Water pressure drop 0.6 psi

Max temperature 85C

Ave top tooth temperature 68C

Ave bottom tooth temperature 60C

Water pressure drop 0.9 psi

Max temperature 63C

Ave top tooth temperature 59C

Ave bottom tooth temperature 51C

Incumbent Stave BMC Ultra-Life Stave

Heat Load ~60 kW/m2

With Refractory

Current Operating Condition

Linear Material Structural Setup

Linear Material Structural

Setup

Linear Material Static

Structure

• Duplicate geometry and link to static structure analysis• This can allow minor changes like a surface split without rerunning

CFX

• Can add minor details such as standoffs or bolts that aren’t necessary

for CFD

• Use linear material for the first structure simulation for metals

• Suppress fluids domain

• Import thermal load from CFX result.

Stave Load and Support

Bolts – Fixed End Support

Pins - Sliding Support by Shell

Backside - Support by

Grout to Shell

Pipes – Bellows free on axial, fixed on

side loads

Bolts – Fixed End Support

Pipe Manifold –

Welded to Shell

Incumbent Stave Design Ultra-Life Stave Design

Backside - Support by

Grout to Shell

Gravity down Gravity down

Constrain – BMC Ultra-life

• Bolt preload:

• Fixed support at bolt end and pipe mount end

• Compression only support – because grout fills the space between

the stave and the furnace shell. This allows the stave to move away

from the shell but not toward the shell

Constraints

Incumbent Stave

• Fixed support at bolt end, Frictionless support on pin body,

Compression only support on stave back and Bolt preload:

• Pipe support to simulate bellows:• Cylindrical supported on 1/8’’ ring

• Free on axial and tangential direction

Cylindrical support

Import CFX Results

for Thermal Load

Step 4 right mouse button to get Import Load

Structural Analysis Settings

for Difficult to Solve

Thermal Load

Compression only restraint and large thermal deflection was difficult to

converge. Smaller thermal loads converged ok. Needed to change analysis

settings to converge – turn Large Deflection On and make 50 substeps

Structural Analysis Settings

Multi-cores

Tools -> Solve Process Setting -> Advanced

Structural Analysis

Results Comparison

Linear Material

Structural Analysis

Results Comparison


Heat Load 500 kW/m2

No Refractory

Incumbent BMC Ultra-Life

Stave Plate Stress Front Side

Orange is Above Yield of 7.2 ksi

Red is Fracture Above 50 ksi

Incumbent

Water Pipe Stress

Orange is Above Yield of 7.2 ksi

Red is above Fracture of 50 ksi

Pipe Thermal Side Displacement .200”

BMC Ultra-Life

BMC Water Pipes

Do Not See Thermal

Stress Because They

Enter and Exit at a Zero

Motion Location


Heat Load 500 kW/m2

No Refractory

Displacement towards furnaceIncumbent

.230” .087”

BMC Ultra-Life


Heat Load 500 kW/m2

No Refractory

Incumbent

Steel Bolt

Yield 95 ksi

BMC Ultra-Life

High Strength

SST Bolt

Yield 160 ksi

Bolt Stress

Orange is Above Yield

Red is Above Fracture

Thermal Side Displacement .115”

Bolt will

FractureBolt will see

Local Yielding

Only

Scaling difference based on bolt

material strength


Heat Load 500 kW/m2

No Refractory

Stave max stress exceeds yield of

7.2 ksi and ultimate of 22 ksiStave body max stress 21 ksi

exceeds yield but below ultimate

Conventional Stave BMC Ultra-Life Stave


Heat Load 60 kW/m2

With Refractory

Non-Linear Material Properties in Engineering Data

Non-Linear Material

Properties

Due to high stress, customer requested non-linear (plastic) analysis

with their current thermal operating conditions. We do not have

non-linear data on copper and had to approximate it.

Non-linear Material

Static Structure

• Copper is ductile material

• The result of linear analysis shows high stress - beyond yield,

where plastic deformation happens. The customer requested non-

linear analysis be used for existing operating conditions (60

kW/m2).

• Select material from non-linear material library or manually input

strain-stress curve

• Large Deflection = ON

Ansys simplifies the curve into bi-linear

hardening with yield strength and tangent

modulus.

Curve for

Tangent modulus = .17 GPa

Later found airforce data

Tangent modulus = .85 Gpa

Both values of Tangent modulus yielded

similar kinematic hardening stress values

Non-linear Material

Static Structure

The plastic curve is fairly

flat after yielding

For non-linear analysis, the tangent

modulus is approximate with

Young’s Modulus/1000, which is 115

MPa. In the plastic region the stress

in this copper doesn’t increase

significantly compared to strain, see

the graph.

Ansys document gives suggestion when

no data of Tangent Modulus is given:

Er = E/1000

USE WITH CAUTION!!!

User input Yield Strength and Tangent Modulus

Nonlinear Material Setting

Non-linear Material

Static Structure

Non-Linear Material Analysis

Non-linear Material

Static Structure

Different Meshing

– Mechanical vs. Non-linear Mechanical

Mechanical Meshing

Nonlinear Mechanical

Meshing

Set Nonlinear Mechanical Mesh

for nonlinear analysis

With the same settings, the

nonlinear mechanical mesh is finer

Non-linear Material

Static Structure

Monitor Solver Process for both

Structural Linear and Non-Linear

Non-linear Material

Static Structure

Note – Interrupt with restart can only be

used after a step or substep is solved

Incumbent Stave Stress

Front and Back Side - Linear

Non-linear Material

Static Structure

60 kW/m2


Incumbent Stave Stress Front

and Back Side – Non-Linear

Local stress near pins and pipes

are well above yield and ultimate

Local stress near pins and pipes

are above yield but below ultimate

BMC Ultra-Life Stave Stress

Front and Back Side - Linear

Non-linear Material

Static Structure

60 kW/m2

Current Operating ConditionBMC Ultra-Life Stave Stress Front

and Back Side – Non- Linear

Local stress near manifold

mount are above yield but

below ultimate

Local stress near manifold

mount are slightly above yield

but below ultimate

Difference Between Linear and


Incumbent

Linear Analysis

104 ksi

Incumbent

Non-Linear Analysis

11 ksi

Equivalent Stress

Equivalent Stress

Incumbent Pipe Stress –

Non- Linear Shear Stress

4.5 ksi stress vs 4.7 ksi shear

yield strength

Temperature spikes or low

cycle fatigue can create

fracture

Incumbent Pipe Stress –

Linear Shear Stress

60 ksi stress vs 4.7 ksi shear

yield strength

Well above fracture

Difference Between Linear and


Shear Stress

Shear Stress

Incumbent Stave

X-axial Displacement,

(radial in) .023”

Y-axial Displacement,

(vertical) .078”

Z-axial Displacement

(sideways) .030”

BMC Stave

X-axial Displacement,

(radial in) .012”

Y-axial Displacement,

(vertical) .055”

Z-axial Displacement

(sideways) .024”

Non-linear Material

Static Structure

60 kW/m2


BMC Ultra-Life Bolt Stress

Does not exceed yield

53 ksi vs 160 ksi yield

Can accommodate preload and

temperature spike as well as

higher temperature

Incumbent Bolt Stress

Approaches Yield

88 ksi vs 95 ksi yield

Preload or a temperature spike

will exceed yield strength of the

bolt

Non-linear Material

Static Structure

60 kW/m2


• Incumbent stave pipe shear stress in plastic analysis is operating near shear yield - thermal

spikes or low cycle fatigue can cause failures. Customer is currently experiencing pipe

cracking at the welds. BMC design does not have pipe stress.

• Incumbent stave pipe bending stress exceeds yield strength and bends. Using plastic

analysis the stress is in a range that may experience low cycle fatigue causing failures.

BMC does not have non-linear data to interpret the results further.

• BMC design does not have pipe stress.

• Incumbent bolt stress is just below yield – thermal spikes or preload on the bolt can cause

bolt failure. Other customers have experienced bolt failure, this customer is planning to

check bolts.

• BMC bolt design has plenty of margin.

• Incumbent stave has larger deflection (2x more) towards the furnace than the BMC design.

• BMC stave operates 30% cooler temperatures. Copper and refractory have higher strength

at lower temperatures

• In the event that all refractory is lost, the BMC stave operates at lower temperature, lower

deflection and less stress than the incumbent design and will survive longer.

Summary of Results

Stave Analysis

Questions?

Stave Analysis

Engineering Analysis of Furnace Stave with ANSYS Metal Stave Analysis ANSYS...Engineering Analysis...

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