1 of 15
A Comparison of Refractory Lined Carbon Steel and Titanium EXW
Clad Pressure Vessels for Specific Operating Conditions
W. Bristowe, M. Pearson, and C. Stunguris
Hatch Ltd.
Oakville, Ontario, Canada
S. Gothard
W.E. Smith Engineering Ltd.
Coffs Harbour, New South Wales, Australia
ABSTRACT
Pressure vessels in hydrometallurgy and many chemical process industries
throughout the world require the use of specific lining systems to protect the parent
vessel materials from corrosion and/or abrasion. Typically, these lining systems are
required for processes that are corrosive and operate at elevated temperatures. Two
basic lining system types are: 1) refractory linings in conjunction with an
impervious corrosion resistant membrane, and 2) metal-clad vessels consisting of
titanium or other corrosion resistant metal bonded to a carbon steel shell.
Operating conditions play a key role in selecting the type of lining system to be
utilized for a specific application. Lining systems in turn have an impact on the
process vessel size, which ultimately affects the capital cost of the vessel. In
addition to the cost of the process vessel, the cost of each type of lining system must
be considered, as well as maintenance concerns, quality control, and delivery.
Operating conditions play a key role in the final selection of lining systems utilized
for specific projects based on initial capital cost, life-cycle maintenance costs, and
overall service life.
This paper examines the fundamentals of each lining system, their inherent
technical strengths and weaknesses, and presents relative cost comparisons for each
lining system as they apply to specific operating conditions and vessel sizes.
2 of 15
INTRODUCTION
Hydrometallurgical process engineers have successfully utilized both refractory
lined and alloy clad pressure vessels in many different process plants. Prime
examples where these types of vessels are used include high-pressure acid leach or
pressure oxidation facilities for the extraction of metals such as gold, copper, cobalt,
nickel, zinc, and uranium. In such facilities, the autoclaves, flash vessels, and slurry
heater vessels are candidates where these types of lining systems are utilized. This
paper focuses on metallurgical autoclave technologies; however, some of the
material is also relevant to other chemical processing industries that require the use
of lined or clad pressure vessels.
Typically, the processes utilised in such facilities operate at elevated temperatures
and pressures in very aggressive and corrosive environments that require a high
degree of corrosion resistance. Refractory lining systems have been used
successfully for many years in these environments. Refractory lining systems utilize
an impervious corrosion resistant membrane protected by a refractory layer that is
exposed to the process environment. The refractory is required to protect the
membrane from high temperatures and abrasion, since the membrane materials
themselves have generally poor thermal and abrasion resistance. Recently,
explosion-clad pressure vessels have gained significant use in high-pressure
autoclaves for the extraction of nickel and other metals. Clad vessels consist of a
corrosion resistant alloy, typically titanium, which has been explosion bonded to a
carbon steel shell. In this type of vessel, the titanium cladding material acts as the
corrosion barrier and is exposed directly to the process environment.
In many instances, the decision to utilize either a titanium clad vessel or a refractory
lined vessel must be made in the feasibility stage of a project, a difficult choice
considering the limited knowledge that exists at the outset of a new project. Both
types of lining systems have their own advantages and disadvantages. When it
comes time to build a demonstration plant or a commercial scale plant, economic
factors determine that decision in most instances. In such cases, all of the factors
such as installed capital cost, process risk, maintenance costs, and service life must
be considered to make that initial critical decision. This paper intends to highlight
specific operating conditions, in conjunction with the listed economic factors,
which may make one lining system more favourable than another for certain
conditions.
3 of 15
Refractory Lining Systems
The basis of a refractory lining system is the impervious corrosion membrane that is
applied to the carbon steel shell. Typical membranes that have been used
successfully in the past are homogeneously bonded lead, nickel alloy weld overlay,
acid resistant rubber membranes, vinyl ester membranes, as well as other
proprietary materials offered by companies specializing in refractory linings. A
refractory lining is required to protect the corrosion resistant membrane. Due to the
temperature limitations of the corrosion membrane, the main function of the
refractory is to thermally insulate the membrane from high process temperatures.
The second function of the refractory is to protect the membrane from abrasion due
to slurry flow induced by agitation (autoclaves), high velocity flash steam (heater
vessels) or high velocity slurry jets (flash vessels). Due to the fixed thermal
conductivity of a refractory materials and the temperature limited membrane,
additional refractory must be added as process temperatures increase in order to
maintain an acceptable membrane temperature.[1] This in turn requires a larger
vessel shell in order to maintain a desired process diameter or process volume. For
this reason, refractory lined vessels will always be larger and heavier than a titanium
clad vessel for the same working pressure, process diameter, and volume. Table 1
presents some of the advantages and disadvantages of refractory lined systems.
Table 1 – Refractory Lining Systems: Advantages and Disadvantages
Advantages Disadvantages
Good corrosion resistance in sulphuric acid environments
Higher maintenance costs associated with face course re-lines
Excellent abrasion resistance Requires larger vessel to accommodate thickness of refractory lining
Excellent resistance to oxidation and ignition (pyrophoricity)
Lower service temperature, due to stability limitations in lining thickness
Titanium Clad Lining Systems
Alloy clad lining systems utilize a layer of corrosion resistant material that is bonded
to a carbon steel parent material. Cladding materials can be titanium, tantalum,
specialty stainless steels or nickel alloys. The most common cladding material in
metallurgical processing plants is explosion bonded titanium which is utilized due
to it’s excellent corrosion resistant properties, ductility, and relatively low cost.[2]
Table 2 summarises some of the advantages and disadvantages of titanium clad
lining systems.
4 of 15
Table 2 – Titanium Clad Lining Systems: Advantages and Disadvantages
Advantages Disadvantages
Excellent corrosion resistance in oxidizing environments.
Potential for ignition in enriched oxygen environments (pyrophoricity).
Titanium can be in direct contact with
process media, resulting in smaller and lighter vessel.
Reduced abrasion resistance, especially to slurries of sulphide ores.
High temperature limitations – up to 315°C (600°F) permitted by ASME Code.
Susceptible to pitting and/or crevice corrosion in reducing environments.
Figure 1 indicates the relative unit costs of fabrication for carbon steel, lead lined
autoclaves and titanium clad carbon steel autoclaves as a function of total vessel
weight. All vessels are constructed of ASME SA-516 Gr. 70 normalised C-Mn-Si
steel. Fabrication unit costs for several sizes of flash vessels other refractory lined
vessels are also indicated for reference. The lower unit cost for these vessels can be
attributed to a simpler vessel design with fewer nozzles and smaller length to
diameter aspect ratios.
Relative Fabricated Unit Cost vs. Vessel Weight
0.0
0.5
1.0
1.5
2.0
2.5
0 100,000 200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000
Total Vessel Weight (kg)
Re
lati
ve
Fa
bri
ca
ted
Co
st
pe
r U
nit
We
igh
t
Ti EXW Clad A/C's
CS/Brick Lined A/C's
CS/Brick Lined Flash Vessels
CS/Brick Lined Other Vessels
Log. (Ti EXW Clad A/C's)
Power (CS/Brick Lined Flash Vessels)
Poly. (CS/Brick Lined A/C's)
Figure 1 – Relative Fabrication Unit Costs as a Function of Vessel Weight
5 of 15
The data points indicated in Figure 1 are derived from project data on actual vessels
that have been fabricated and placed into service, as well as firm and budget
quotations from vessel manufacturers. The relative fabricated unit costs presented
are Ex Works and include material, fabrication labour, consumables, non-
destructive examination, engineering, quality control, overhead and profit. Freight
costs are excluded so as remove regional disparities from the comparison. All costs
have been indexed to third quarter 2010 US Dollars, using the Marshall and Swift
Equipment Cost Index, and currency exchange rates at the time of order placement.
An expected trend in Figure 1 indicates that the fabricated unit cost of titanium
EXW clad vessels and carbon steel, brick lined flash vessels decreases as the vessels
get larger and heavier. This trend has been confirmed in conversations with vessel
manufacturers.
The reasons for this trend are as follows:
i) The fixed costs associated with the manufacture of a vessel such as
engineering, quality control, and overhead are distributed. Therefore, these
fixed costs will drive up the unit price of a smaller vessel, while in a larger
vessel these costs are distributed over more weight, resulting in a lower unit
cost.
ii) On larger vessels, the labour cost per kilogram of material is reduced since
automated welding machines provide more output on larger vessels and
heavier wall thicknesses.
iii) In addition to the fixed costs and larger output from automated machinery,
this trend is also affected by the fact that the percentage of costs associated
with additional material and fabrication for nozzles, clips, internals and
cladding becomes smaller as the vessels become larger.
The three factors affecting this trend hold true for the fabrication of titanium clad
vessels, refractory lined carbon steel flash vessels and solid alloy vessels, however
no such trend has been observed in the unit fabrication cost of refractory and lead
lined carbon steel autoclave vessels.
The absence of this trend in horizontal refractory lined vessels indicates that as
vessels get larger, the unit cost to fabricate a vessel decreases until a threshold is
reached which requires a step change in shell diameter and nozzle sizes (and vessel
cost) to accommodate additional refractory brick. In addition, as the diameter of the
vessel increases to accommodate another course of refractory brick, the shell
thickness and total weight of the vessel increase proportionally to the vessel
diameter.[1]
6 of 15
Design Conditions
Process conditions vary greatly from one process to another when it comes to the
design of metallurgical processing plants. The following table indicates some of the
typical process conditions and environments that can be found in some
metallurgical processing facilities currently in production or detailed engineering
design stages.
Table 3 – Process Conditions found in Metallurgical Processing Facilities
Operating Conditions*
Hydrometallurgical Process Temperature
°C
Pressure
kPa(g)
Typical Uses
High Pressure Acid Leach 250 – 275 4500 – 6300 Ni Laterite ore leaching
Bayer™ Alumina Process 260 – 280 7000 - 8000 High temperature caustic digestion
Total Sulphide Oxidation 200 – 235 2000 – 3500 Refractory gold sulphide
ore treatment
Acid Pressure Leaching 180 1730
Alkaline Carbonate Leach 120 350
Oxidative leaching of
uranium, rare earth ores
Freeport McMoRan Process 160 2000
CESL Process – Chloride assisted partial oxidation
130 – 155 1100 - 1275
Oxidative leaching of
chalcopyrite & Cu matte
Activox™ Process – Low Temp.
Oxidation 110 1000
Oxidative leaching of
Ni/Co concentrates
*Operating conditions do not necessarily reflect actual design conditions. Design conditions will be
higher than operating conditions.
Based on the operating conditions encountered in these metallurgical processing
plants, a matrix was developed to cover a range of operating temperatures and
pressures over a range of vessel sizes. From this matrix, vessel sizes and
corresponding wall thickness, mass, and surface areas etc. were calculated for a
typical six (6) compartment autoclave. Total capital costs were then estimated for
each vessel size.
7 of 15
Table 4 indicates the range of process conditions that formed the basis of the capital
cost comparison between titanium clad and refractory lined pressure vessels.
Table 4 – Process Conditions and Vessel Sizing Matrix*
Normal Operating Conditions
Normal Operating Temp. °C 150 175 200 225 250 275 300
Normal Non-condensable
Overpressure
kPa (abs) 350 350 350 350 350 350 350
Normal Operating Press. kPa (abs) 825 1242 1905 2900 4328 6299 8943
Maximum Operating Conditions
Maximum Operating Temp. °C 160 185 210 230 255 280 305
Max. Non-condensable
Overpressure
kPa (abs) 350 350 350 350 350 350 350
Maximum Operating Press. kPa (abs) 967 1473 2258 3148 4674 6770 9564
Design Conditions
Design Margin on MOP 10% 10% 10% 10% 10% 10% 10%
Design Temperature °C 164 189 215 235 261 286 312
Design Pressure – absolute kPa (abs) 1064 1621 2484 3463 5142 7447 10520
Design Pressure – gauge kPa (g) 963 1519 2383 3361 5041 7346 10419
ANSI Pressure Class 150 300 300 300 600 600 900
*Vessel process diameters range from 2.0 m thru 6.0 m in 0.5 m increments
Capital Cost Comparison
The costs included in the analysis for each vessel type are listed in Table 5. All unit
costs are derived from previous project data and are corrected to third quarter 2010
US Dollars using Marshall and Swift equipment cost indices.
Table 5 – Costs Included in Vessel Comparison
Refractory Lined Vessel Titanium Clad Vessel Solid Titanium Vessel
Vessel Fabrication Labour
Vessel Materials
Lead Membrane or Rubber Membrane
Refractory Lining
Vessel Fabrication Labour
Vessel Materials
Plate EXW Cladding
Exterior Thermal Insulation
Vessel Fabrication Labour
Vessel Materials
Exterior Thermal Insulation
8 of 15
Figure 2 shows the relative component costs for the fabrication of a 4.0 m process
diameter autoclave vessel. The trends indicated on this figure are fairly typical for
all of the other vessels included in the comparison matrix. One of the significant
trends revealed in the figure indicates that at low operating temperatures and
pressures, refractory lined vessels are slightly more economical than a similar sized
titanium clad vessel. In the figure, the lead lined vessels for 150°C and 175°C
conditions are lower in cost compared to the equivalent titanium Gr. 1 clad vessel.
Analyzing the data further reveals that the crossover point where titanium clad
vessels become more economical occurs when three (3) courses of refractory brick
would be required to thermally insulate the corrosion membrane.1 Where this
occurs, the additional labour for the installation of the third course of refractory
exceeds the incremental material and labour costs associated with the fabrication of
a titanium clad vessel.
0.0
1.0
2.0
3.0
4.0
Rela
tive
Co
mp
on
en
t C
ost
Fabrication Materials
Cladding / Membrane Insulation / Refractory
TITANIUM
CLAD
AUTOCLAVE
REFRACTORY
LINED
AUTOCLAVE
Design Temperature,°C
15
0
17
5
20
0
22
5
25
0
27
5
15
0
17
5
20
0
22
5
25
0
27
5
Figure 2 – Total Autoclave Cost as a Function of Vessel Operating Temperature
(4.0 m diameter vessel shown)
1 175°C is only a guideline that has been calculated with certain refractory brick conductivities,
membrane conductivities, convection and radiation coefficients. A detailed thermal calculation
should be performed to confirm the required brick thickness and corresponding courses of brick
required for a particular service.
9 of 15
An additional factor contributing to the higher overall cost of the refractory lined
vessel at higher operating conditions is that the vessel itself must be progressively
larger to accommodate the additional courses of refractory while maintaining the
same process volume. Although the unit cost of the carbon steel vessel is lower
than the unit cost to fabricate a titanium clad vessel, the carbon steel vessel ends up
being more expensive than the clad vessel due to the additional weight and
additional material required. Figures 3A & 3B illustrate the significant increase in
refractory lined vessel costs as the design temperature (and pressure) increase due to
additional refractory being required to protect the corrosion resistant membrane. At
high temperatures and pressures, the costs for a refractory lined vessel could be
50% - 60% higher than the cost of a titanium clad vessel with the same process
diameter.
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
0
2
4
6
8
10
12
14
16
18
Rel
ativ
e V
esse
l C
ost
Vessel Process Diameter, m
150°C
175°C
200°C
225°C
250°C
275°C
Figure 3A – Relative Ti Gr. 1 Clad Autoclave Cost vs. Process Diameter &
Operating Temperature
10 of 15
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
0
2
4
6
8
10
12
14
16
18R
elative
Vess
el C
ost
Vessel Process Diameter, m
150°C
175°C
200°C
225°C
250°C
275°C
Figure 3B – Relative Lead/Refractory Lined Autoclave Cost vs. Process Diameter &
Operating Temperature
While considering the low temperature and low-pressure applications, it should be
noted that a cost comparison was also made with solid titanium alloy constructed
vessels. This comparison revealed that at low operating temperatures and pressures
and corresponding vessel sizes, a solid titanium vessel would be more economical
than either a titanium-clad or refractory lined vessel. According to the calculations
for estimated capital costs, this trend holds true for solid alloy vessels up to a wall
thickness range of 20 – 25 mm. This trend confirms what vessel fabricators and
clad plate suppliers have indicated in past discussions and published documents by
Banker [2, 3]. Above this thickness, the additional titanium material costs required
to fabricate a solid vessel exceed the additional labour required to fabricate a clad
vessel, and clad construction becomes more economical. Some fabricators have
indicated that there is approximately 10% more labour involved in the fabrication
of a clad vessel as written by DeGaspari [4]. This additional labour is attributed to
the additional work associated with batten strap welding.
11 of 15
Other Cost Considerations
Cladding Thickness
All of the costs presented for titanium clad vessels assume that the vessel is clad
with 8 mm thick EXW titanium, as is common with autoclaves currently in use for
high-pressure acid leaching (HPAL) of nickel and cobalt. Other cladding thickness
such as 3 mm, 5 mm, and 6 mm are also available and commonly used and can
reduce the overall capital cost of the vessel. A cost comparison of 5 mm cladding
versus 8 mm cladding was performed to determine the sensitivity of overall vessel
capital cost with respect to cladding thickness. This analysis revealed that a
premium in the range of 1% to 3% of overall capital cost is paid for 8 mm cladding
over 5 mm cladding. As expected, this general trend indicated that the 3%
premium was noticed on the thinner walled, lighter vessels operating at lower
temperatures and pressures while the 1% premium exists for thicker walled, heavier
vessels operating at higher temperatures and pressures.
Alternative Materials of Construction
In refractory lining systems, specific process conditions (HCl, metal chlorides,
halides) may require more expensive brick alternatives. Also, lining materials such
as homogeneously bonded lead, rubber, and vinyl ester membranes vary
significantly in material and installation labour cost. For titanium clad materials,
different grades of titanium will be selected for particular services. Table 6 indicates
some of the alternative selections and relative cost premiums for each material.
Table 6 – Alternative Material Selections and Relative Cost Premiums
Relative Cost2
Titanium Clad Lining Systems Range Average
Ti Gr.1 EXW on SA-516 Gr. 70N 1.00 1.00
Ti Gr.7 EXW on SA-516 Gr. 70N 1.04 – 1.20 1.12
Ti Gr.11 EXW on SA-516 Gr. 70N 1.03 – 1.11 1.06
Ti Gr.17 EXW on SA-516 Gr. 70N 1.02 – 1.12 1.07
Membrane/Refractory Lining Systems Range Average
Lead/Fireclay Brick on SA-516 Gr. 70N 1.00 1.00
Bromobutyl Rubber/Fireclay Brick on SA-516 Gr. 70N 0.82 – 0.96 0.90
Vinyl Ester/Fireclay Brick on SA-516 Gr. 70N 0.77 – 0.94 0.87
Bromobutyl Rubber/Visil™ Brick on SA-516 Gr. 70N 0.90 – 1.00 0.96
Vinyl Ester/Visil™ Brick on SA-516 Gr. 70N 0.85 – 0.98 0.93 2 Relative costs are based on total estimated capital costs, and vary within the ranges specified
with vessel size, mass, and operating conditions.
12 of 15
Titanium Grade 1 material is shown as the base case for titanium clad vessels and is
suitable for many applications. The use of higher-grade alloys provides increased
crevice corrosion and pitting resistance that may be required for certain
applications.[3] Note that the relative costs of each material option are not constant
as shown by the ranges listed in the table. The range indicated in the table is the
relative cost over the range of different vessel sizes and operating conditions
considered herein. In general, the high value indicated occurs in the lower
temperature and pressure applications. This is attributed to the material cost
premiums being distributed over a lower initial cost, therefore the percentage
increase is greater.
The base case for refractory lined systems is a homogeneously bonded chemical
lead membrane with acid resistant fireclay brick. Other membrane options
included in the table are bromobutyl rubber and vinyl ester membrane. These
membrane options could potentially be combined with high silica grade refractory
such as Visil™ brick for use in high chloride environments. The range of relative
costs shown for these material combinations is attributed to the varying vessel sizes
and operating conditions.
It is very important for the materials engineer to understand all of the normal and
upset process conditions in order to select the proper materials of construction for a
specific process. Pilot plant testing of candidate materials is recommended when
new processes and process environments are encountered in the feasibility study
stage of a project. These initial decisions can have a significant effect on the
resulting capital cost of the vessels, and potential impact on project schedules.
Maintenance Issues and Quality Control
Both refractory and titanium clad lining systems both have the potential to provide
dependable and satisfactory service for the design life of most process facilities.
Acid resistant fireclay brick/lead lined Pachucca reactors have been used in 245°C
HPAL service at Moa Bay, Cuba since 1958. Titanium Gr. 1 EXW clad autoclaves
have been in 250°C HPAL service at Murrin Murrin (Minara Resources) in Western
Australia since 1999.[3] To ensure that maintenance issues are minimized it is
important that both types of lining systems are properly engineered and that suitable
fabrication techniques, quality control, and installation procedures are followed.
Refractory lining systems generally require routine inspections and maintenance
involving the cleaning and re-pointing of mortar joints on an annual basis. This
requirement varies with selected mortar (potassium silicate, litharge, furanic and
phenolic resin-based mortars) as well as actual process environments. Refractory
lining life is also limited by swelling and softening of brick in the vapour zone of
refractory sulphide pressure oxidation service, and generally requires a complete
13 of 15
face course reline every 5 – 7 years of operation. Due to these maintenance
requirements, refractory lining systems have higher associated maintenance costs.
Titanium clad lining systems are expected to have lower maintenance requirements
than refractory lined systems. However, this is only achievable with the selection of
suitable material grades for the process environment, proper vessel design, quality
assurance, and fabrication techniques. Titanium weld repair of clad vessels that
have been in service is challenging due to the environmental (cleanliness)
requirements for welding and purging.[5] If all of these factors are executed
properly, titanium clad linings are expected to provide equally long service life.
Delivery and Scheduling
Project schedule requirements should be considered in selection of a lining system
since they may limit the selection of specific lining systems. When selecting a
lining system, it is important to have a clear understanding of the material lead time,
fabrication and delivery associated with each system. A titanium clad vessel has a
longer material procurement time in receiving clad plate from suppliers, whereas a
lead lined vessel has a shorter time for material procurement, but a much longer
fabrication time due to the labour-intensive lead brazing process. Figure 4 shows
the relative fabrication, transport, and installation duration for titanium clad and
lead/refractory lined autoclave vessels.
0.70
0.80
0.90
1.00
1.10
1.20
1.30
1.40
Ti Flush
Batten
Ti Conv
Batten
Pb Lined
Brick Lining
Installation
Transport
Pb Lining
Vessel Fabrication
Figure 4 – Relative Schedule Duration for Ti Clad vs. Lead/Refractory Lined
Autoclave Vessels
14 of 15
A typical delivery period for a large titanium clad autoclave is in the range of 22 –
24 months. For a similar sized carbon steel, lead lined vessel, the delivery period is
estimated to be 28 months, plus 2 months to complete the brick lining on site for a
total of 30 months. Naturally, these delivery periods vary considerably and should
be confirmed for a specific project as they are dependant on vessel size, material
availability at the time of purchase, and vessel fabricator shop loading.
Conclusion
The selection of a specific lining system calls for sufficient knowledge of process
requirements related to vessel sizing, operating conditions and environments,
maintenance concerns, and fabrication and installation schedules. The relative cost
comparison presented reveals that refractory lining systems are cost effective at
lower operating temperatures and pressures over a range of vessel sizes. As process
temperatures increase, titanium clad vessels become significantly more economical.
Process environments that may require more expensive materials selection must be
evaluated on a case by case basis and have potential to significantly affect capital
costs. Maintenance requirements of refractory systems are generally higher,
although with proper material selection, design, fabrication and installation
procedures, maintenance issues can be reduced for both types of lining systems.
With a complete evaluation of operating conditions, materials selection,
maintenance, and schedule requirements, capital cost estimates can be generated
and suitable lining candidates can be selected.
15 of 15
REFERENCES
1. A. Koning and P. Lauzon, “Design Fundamentals for hydrometallurgy pressure
vessel refractory linings”, Proceedings of the International Conference on the
Use of Pressure Vessels for Metal Extraction and Recovery, 34th Annual
Hydrometallurgy Meeting of CIM, Banff, Canada, 2004, pgs. 617 - 638
2. J.G. Banker, Titanium Clad Autoclave Performance in Nickel Laterite
Hydrometallurgy, Clad Metal Products Inc., Boulder, Colorado, USA.
www.clad-metal.com
3. J.G. Banker, “Hydrometallurgical Applications of Titanium Clad Steel”, Reactive
Metals in Corrosive Applications, Sun River, Oregon, USA, 1999
4. J. DeGaspari, “Titanic Proportions”, Mechanical Engineering Magazine, March
2000.
5. W. Bristowe, A. Hanson, and M. Pearson, “Quality assurance programs for
fabrication of specialised vessels and exotic alloy piping”, Proceedings of the
International Conference on the Use of Pressure Vessels for Metal Extraction
and Recovery, 34th Annual Hydrometallurgy Meeting of CIM, Banff, Canada,
2004, pgs. 385 – 400.
ACKNOWLEDGEMENTS
The authors wish to acknowledge and thank the following people who provided
fabrication and material costs, design data, and technical support for the preparation
of this paper.
1. John G. Banker, President, CLAD Metal Products Inc., Boulder Colorado, USA.
2. R. Henson, Manager, Business Development, Uniti Titanium Ltd.
3. Julien Laermans, Commercial Manager, COEK Engineering N.V., Belgium.
4. Don Want, Engineering Manager, W.E. Smith Engineering Ltd., Coffs Harbour.
5. Paul Trotman, Manufacturing Manager, W.E. Smith Engineering Ltd., Coffs
Harbour.
A Comparison of Refractory Lined, Carbon Steel and Titanium EXW Clad Pressure Vessels for Specific Operating Conditions
S. GothardW.E. Smith Engineering Pty Ltd.
W. Bristowe, M. Pearson, C. StungurisHatch Ltd.
Introduction
Lead/Refractory Lined Autoclave
Ti Explosion Clad Autoclave
Typical Generic Membranes:• Homogeneously Bonded Lead• Panel Bonded Chemical Lead• Chlorobutyl Rubber• Bromobutyl RubberProprietary Membranes:• Derakane™ Vinyl Ester Resin• Pyroflex™ Bitumous Sheet
• Typical refractory lining system consists of an impervious membrane applied to a carbon steel shell.
• A refractory layer is applied to protect the corrosion membrane from high temperature and abrasion.
Bac
kgro
und Refractory Lining Systems
Refractory Lining Systems
Advantages• Good corrosion
resistance in sulphuric acid environments.
• Excellent abrasion resistance.
• Excellent resistance to oxidation and ignition (no pyrophoricity).
• Easy to replace damaged bricks and mortar.
Disadvantages• Requires larger vessel to
accommodate refractory.• Temperature limited by lining
stability and vessel diameter.• Refractory is susceptible to
structural damage due to rapid vessel depressurization.
• Increased maintenance costs associated with replacement of face course in 5 – 7 years.
• Refractory and mortar may be susceptible to degradation in vapor zone.
Bac
kgro
und
Metal Clad Lining Systems
• Corrosion resistant alloy is bonded to a carbon steel parent metal to protect the vessel pressure boundary.
• Preferred method of bonding is explosion cladding• Requires specialized fabrication techniques and batten
strap welding by experienced fabricators.
Bac
kgro
und
Typical Cladding Materials:• Titanium (Gr. 1, 7, 11, 17)• Zirconium• Tantalum• Ni alloy (Inconel™,
Hastelloy™)• Super austenitic stainless
steel (904L)
Titanium Clad Lining Systems
Advantages• Excellent corrosion
resistance in oxidizing environments.
• Upper temperature limit of 600°F (315°C).
• Titanium can be in direct contact with process media resulting in smaller and lighter vessels.
• Fewer limitations on transportation routes and types of transporters due to lighter vessel weight.
Disadvantages• Potential ignition in enriched
oxygen environments (pyrophoricity)
• Reduced abrasion resistance• Susceptible to pitting and/or
crevice corrosion in reducing environments.
• Susceptible to damage at free acid concentration > 10% w/w H2SO4
• Requires frequent de-scaling for corrosion inspection
• Repairs difficult to perform; require specialised welders.B
ackg
roun
d
Des
ign
Hydrometallurgical Process
Temp(°C)
PressurekPa(abs)
Typical Uses
High Pressure Acid Leach 250275
45006300
Ni Laterite ore treatment
Bayer™ Alumina Process 260280
70008000
High temperature caustic digestion
Total Sulphide Oxidation 200235
20003500
Refractory Au sulphides ore treatment
Acid Pressure Leaching 180 1730 Oxidative leaching of uranium & rare earth oreAlkaline Carbonate Leach 120 350
Freeport McMoran 160 2000 Oxidative leaching of chalcopyrite and Cu matte
CESL Process – Chloride Assisted Partial Oxidation
130155
11001275
Activox™ Process – Low Temp. Oxidation
110 1000 Oxidative leaching of Ni/Co concentrates
Operating Conditions
Des
ign
Design Conditions
Normal Operating ConditionsTemperature °C 150 175 200 225 250 275
Pressure kPa(abs) 825 1242 1905 2900 4328 6300
Maximum Operating ConditionsTemperature °C 160 185 210 230 255 280
Pressure kPa(abs) 934 1473 2258 3148 4674 6770
Design Conditions
Temperature °C 164 189 215 235 261 286
Pressure kPa(g) 963 1519 2383 3361 5041 7346
ANSI Class 150# 300# 300# 300# 600# 600#
Capital Cost Analysis
Refractory Lined Vessel
Titanium Clad Vessel
Solid Titanium Vessel
Fabrication Labour Fabrication Labour Fabrication LabourMaterials Cost Materials Cost Materials CostImpermeable
Membrane (Lead, Rubber, etc.)
EXW Cladding Exterior Thermal Insulation
Refractory Lining Exterior Thermal Insulation
All unit costs have been derived from previous project data and are corrected to Q3 2010 United States Currency using Marshall and Swift Indices.
Cos
ts
Cos
tsCapital Cost Analysis
• Equipment Data: has been retrieved from actual hydrometallurgical plants currently in service.
• Equipment Costs: based on firm and budget quotations from vessel fabricators.
• Material Costs: are based on supplier unit costs in for plate material at the time of writing.
• Vessel Fabrication: unit costs are back calculated on a fabricated weight basis.
• Membrane costs: based on previous project costs. Unit costs are back calculated on a per m2 basis.
• Refractory costs: based on previous project costs. Unit costs have been back calculated on a per m2
per course basis.
Relative Fabrication CostsC
osts
Relative Fabricated Unit Cost vs. Vessel Weight
0.0
0.5
1.0
1.5
2.0
2.5
0 100,000 200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000
Total Vessel Weight (kg)
Rel
ativ
e Fa
bric
ated
Cos
t per
Uni
t Wei
ght
Ti EXW Clad A/C'sCS/Brick Lined A/C'sCS/Brick Lined Flash VesselsCS/Brick Lined Other VesselsLog. (Ti EXW Clad A/C's)Power (CS/Brick Lined Flash Vessels)Poly. (CS/Brick Lined A/C's)
Relative Fabrication Costs
Vessel fabricated unit costs decrease as vessels get larger and heavier. This is due to the following:
• Fixed costs associated with manufacture (engineering, quality control, overhead) distributed over a larger vessel.
• The labor cost per unit weight of material is reduced on larger vessels since there is higher deposition rates from automated welding machines and higher quality of welds leading to less rework.
• Percentage of costs associated with additional material and fabrication of nozzles, clips, internals, etc. becomes smaller as vessels become larger.
Cos
ts
Component CostsC
osts
0.0
1.0
2.0
3.0
4.0
Rela
tive
Com
pone
nt C
ost
Fabrication MaterialsCladding / Membrane Insulation / Refractory
TITANIUM CLAD
REFRACTORY LINED
Design Temperature,° C
150
17
5
200
22
5
250
27
5
150
17
5
200
22
5
250
27
5
Ti Clad Vessel Relative Costs C
osts
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
02468
1012141618
Rela
tive
Ves
sel C
ost
Vessel Process Diameter, m
150° C175° C200° C225° C250° C275° C
Refractory Lined Vessel Costs
Cos
ts
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
02468
1012141618
Rela
tive
Ves
sel C
ost
Vessel Process Diameter, m
150° C175° C200° C225° C250° C275° C
Solid Titanium Alloy VesselsC
osts
Cost Comparison
70%
75%
80%
85%
90%
95%
100%
Ti FlushBatten
Ti ConvBatten
Pb Lined
Brick LiningVessel Ex Works
Autoclave cost difference based on same process volume.
Cos
ts
• Cladding Thickness• Specific Materials of Construction• Maintenance and Quality Control• Scheduling and Delivery
Cos
tsAdditional Considerations
Cladding Thickness
• All costs that have been presented use a cladding thickness of 8 mm.
• Sensitivity analysis was performed to compare 8 mm and 5 mm cladding over the range of vessels sizes presented.
• A premium of 1% to 3% of overall capital cost is paid for 8 mm cladding. This cost is mostly due to the additional material required.
• The 3% premium occurs on the thinner walled lighter vessels operating at lower temperatures and pressures while the 1% premium exists for the thicker walled heavier vessels.
Cos
ts
Materials of Construction
• Specific process environments may require ‘upgraded’ materials of construction to withstand certain corrosive environments.
• HCl, metal chlorides, and halides may require more expensive refractory materials.
• Selected membrane materials such as lead, rubber, and vinyl ester vary significantly in material and installation costs.
• More expensive high alloy grades of titanium may be required for crevice corrosion and pitting resistance in certain environments.C
osts
Material Relative Costs
Titanium Clad Lining SystemsRelative Cost
Range AverageTi Gr.1 on SA-516 Gr.70N CS 1.00 1.00Ti Gr.7 on SA-516 Gr.70N CS 1.20 - 1.04 1.12Ti Gr.11 on SA-516 Gr.70N CS 1.11 – 1.03 1.06Ti Gr.17 on SA-516 Gr.70N CS 1.12 – 1.02 1.07Refractory Lining SystemsLead / Acid Resistant Fireclay Brick 1.00 1.00Rubber / Acid Resistant Fireclay Brick 0.82 – 0.96 0.90Vinyl Ester / Acid Resistant FC Brick 0.77 – 0.94 0.87Rubber / VisilTM Brick 0.90 – 1.00 0.96Vinyl Ester / VisilTM Brick 0.85 – 0.98 0.93
Cos
ts
Maintenance & Quality Control
• Both refractory lined and titanium clad lining systems have the potential to provide dependable and satisfactory service for long periods of time.
• Both types of lining systems must be properly engineered and suitable fabrication techniques, quality control, and installation procedures followed.
• Refractory linings require routine inspections 12 –18 months apart for cleaning and re-pointing of mortar joints (varies with selected mortar & process environment).
• Titanium clad lining systems are expected to have lower maintenance requirements, however, this is only achievable with the proper selection of material grades, vessel design, QA, & fabrication techniques.
Qua
lity
Quality Control
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
ExperiencedFabricator
InexperiencedFabricator
Cost of VesselInspection
Qua
lity
Delivery and Schedule
• Titanium clad vessels have a longer lead time due to the time required for receiving clad plate.
• A typical delivery period for a large commercial scale titanium clad autoclave is 22 – 24 months.
• Delivery for a similar carbon steel, lead lined vessel is 28 months, plus 2 months for refractory lining on site for a total of 30 months.
Sch
edul
e
Delivery & Schedule
0.70
0.80
0.90
1.00
1.10
1.20
1.30
Ti FlushBatten
Ti ConvBatten
Pb Lined
Pb LiningVessel Fabrication
Autoclave delivery based on same process volume
Sch
edul
e
Project Schedule
0.70
0.80
0.90
1.00
1.10
1.20
1.30
1.40
Ti FlushBatten
Ti ConvBatten
Pb Lined
Brick LiningInstallationTransportPb LiningVessel Fabrication
Autoclave time to commissioning (1.00 = 90 weeks)
Sch
edul
e
Concluding Comments
• Selection of a specific lining system calls for sufficient knowledge of:– Process requirements related to vessel sizing– Operating conditions and environments– Materials selection– Maintenance concerns– Fabrication and installation schedules
• All of the above impact capital costs as well as long term maintenance costs.
• Refractory lined vessels appear to be more economical at lower temperatures over a range of vessel sizes.
• Titanium clad vessels become more economical at higher process temperatures (> 175°C).
Murray PearsonAutoclave Technology Group - Non-Ferrous
1075 North Service Road - Unit 21Oakville ON Canada L6M 2G2
Office: (905) 469-3401 Ext. 7340Mobile: (905) 484-3401
Email: [email protected]