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MATERIAL SELECTION FOR NITROGEN BASED

FERTILIZERS PLANTS

Author

Prem Baboo

Sr. Manager (Prod)

National Fertilizers Ltd., Vijaipur, India

INTRODUCTION

Materials plays very important role in any industry .Selection of material is vital at design stage

itself. Wrong selection of material may lead to catastrophic failures and outage of plants & even loss

of Human lives. Right selection of material leads to long life of plant. Fertilizer Plants employ

various corrosive, hazardous and abrasive fluids and chemicals. The temperatures involved range

from cryogenic (-330C) in ammonia storage to 10000C in reformer. The pressure are as high as 175-

350kg/cm2 in ammonia converter and in urea plant reactor pressure 150-250 kg/cm2.Once

equipment has been selected, the materials for its construction must be established. Although a

process Engineer is not expected to be knowledgeable as a metallurgist, the engineer should have a

general idea of what materials are compatible with the process. Therefore, this topic presents some

general guidelines in the selection of material for process equipment. In all ammonia, Urea Plants

worldwide the problem of severe erosion and corrosion of high pressure vessel has been a common

phenomenon.

In Ammonia Plants, past experience has shown that duplex stainless steels can successfully

replace carbon steel and stainless steel in most heat exchangers at temperatures below 3000C.The

improved corrosion resistance gives longer service life and what is more important, fewer

standstills. High alloyed duplex stainless steels can even be used for seawater-cooled heat

exchangers. In urea plants the stripping technology has called for special care in the choice of

materials. A wider use of special alloys has resulted in lower maintenance costs and longer service

life. When considering the new materials of construction, one most remember that it takes time to

build up a comprehensive portfolio of corrosion data and case studies supporting their successful

use. For this reason, corrosion-resistant alloys first introduced in the early 1980s are still

considered to be newer.

STAINLESS STEEL

• “Steel that has 12% or more chromium is considered stainless steel.”

• “Another criterion defining a stainless steel is its Passivity.”

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• PASSIVITY - “Passivity is the ability of a metal to form an impervious surface coating which inhibits

corrosion resulting from the electrochemical reaction of the metal with the surrounding

environment.”

• “Stainless Steels exhibit passivity in oxidizing environment.”

To ensure that carbon do not migrate to welding joints (because temperature between 5500C-8500C

during welding this cause depletion of chromium as carbon form) Cr23C6 at grain boundaries in

region adjacent to welds. There is quit serious depletion of chromium and have a weakening of

passivity. Following may be done.

I. Either keep carbon less than 0.03%

II. Add Ti four times of carbon content

III. Niobium eight times of carbon content

Corrosion as function of Chromium

“Following figure No.1 shows the corrosion rate as function chromium content in an iron

chromium alloy.” It might be assumed that increasing the chromium contents without limit would

improve corrosion resistance. This does not happen Figure No.-2 shown the phase diagram for

iron and chromium in all proportions. With Chromium contents between 20 & 70%, the Sigma

microstructure is formed.

Figure No.1

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IRON-CHROMIUM PHASE DIAGRAM

• Following figure No.2 shows the phase diagram for iron chromium in all proportions.

• With chromium contents between 20 and 70%, the “sigma” microstructure is formed.

SIGMA MICROSTRUCTURE.- “This microstructure is hard, brittle and poor

corrosion resistance.”

Figure No.2

TYPES OF STAINLESS STEEL

There are three general types of stainless steel of interest to the process engineer.

1. FERRITIC STAINLESS STEEL

2. AUSTENITIC STAINLESS STEEL

3. MARTENSITIC STAINLESS STEEL

FERRITIC STAINLESS STEEL

• Ferritic stainless steel has a carbon content of 0.2% or less. Fig. No.3

• Chromium content 11-18% .

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• Although it can not be heat treated and has poor tensile and impact strength, it better

corrosion resistance than martensitic stainless steel.

• Highly resistant to stress corrosion cracking show an increases as result of cold work

• They are magnetic, have good ductility readily weldable, non-magnetic

• Welding is difficult

• SS 430(17% Cr) USED FOR AUTOMOTIVE TRIMS

FERRITIC STAINLESS STEEL (Chemical Requirements)

Table No.1

AISI

430

C Mn P S Si Cr

0.12 1.0 0.04 0.03 1 14-18

• It is suitable for use with strong oxidizing acids such as Nitric acid.

Figure No.-3

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MARTENSITIC STAINLESS STEEL

• Farritic stainless steel has a Carbon.-1.2% or less. And Chromium.-12-18%. Fig.No.4

• It has better hardenability and strength than does ferritic stainless steel.

• It is used as cladding to carbon steel for some process vessels.

IRON –CHROMIUM PHASE DIAGRAM FOR 1.0% CARBON

Figure No.-4

MARTENSITIC STAINLESS STEEL

(Chemical Requirements)

Table No.2

AISI C Mn P S Si Cr

410 0.15 1.0 0.04 0.03 1.0 11.5-13.5

420 0.15 1.0 0.04 0.03 1.0 12-14

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AUSTENITIC STAINLESS STEEL

• “Austenitic stainless steel is a more complex material because the addition of NICKEL (3.5 to

22%) allows it to retain its austenitic microstructure at all temperature

• It has a high tensile strength and best impact strength, ductility and corrosion resistance of

all the stainless steel over a very wide range of temperatures.

• All stainless steels are susceptible to pitting from exposure to high chloride concentration.

However, austenitic steel with high Molybdenum content (1 to 3 %) has improved

resistance to pitting.

• The austenitic alloys have a face centered cubic structure which has a better corrosion

resistance compared to the ferritic steels. The austenitic structure is normally not stable in

irons below 7000 C, but adding nickel to the steel makes the austenitic phase stable down to

room temperature

• These alloys are basically chromium nickel steels. Chromium is used in these alloys to make

the steel corrosion resistant, whereas nickel stabilizes the even more corrosion resistant

austenitic structure. Silicon and aluminum are added to increase the oxidation resistance.

Titanium and niobium, as well as boron, nitrogen, tungsten, vanadium and cobalt can be

added to increase the creep strength due to precipitation strengthening. Manganese can be

used to substitute nickel as an austenite former. Fig. No.5

Fe-Cr-Ni Ternary diagram for an 18% Cr alloy with the austenitic

Stainless Steel.

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Figure No.-5

AUSTENETIC STAINLESS STEEL

(Chemical Requirements)

Table No.3

Sr.No. AISI C Mn Si Cr Ni Mo

1 304 0.08 2.0 1.0 18-20 8-10.5 -

2 304L 0.03 2.0 1.0 18-20 8-10.5 -

3 309 0.2 2.0 1.0 22-24 12-15 -

4 310 0.2 2.0 1.0 24-26 19-22 -

5 316 0.08 2.0 1.0 16-18 10-14 2-3

6 316L 0.08 2.0 1.0 16-18 10-14 2-3

7 321 0.08 2.0 1.0 17-19 9-12 TI≥5×C

8 347 0.08 2.0 1.0 17-19 9-12 Nb≥5×C

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STAINLESS STEEL

Table No.-4

Sr.No

.

MEDIA TYPE OF STEEL

13% Cr steel 18/8 Austenitic 18/10+Mo

1 Nitric acid Resist all strength

cold attacked by

strong boiling acid

Attacked only by boiling

concentrated acid

As 18/8

2 Phosphoric

Acid

Attacked by all

strength but less so

in 60-90 range

Resists most strength

point. Slight attack by

boiling 40% and hot 60-

90% attacked by

80%and at 110%

Resist to all

strength up to

boiling point but

attacked by 80%

acid at 1000C

3 Sulphuric

Acid

Attacked by all

concentrations

Slightly attacked by cold

5-10% and by hot &

cold 85-95% acid.

Attacked by hot or cold

15-75% acid

Resistant to hot

and cold 5-10%

acid and to

cold15, 85 & 95%

acid. Slightly

attacked by hot

15.85 & 95% acid

attacked by hot

20% and cold40-

70% acid

4 ammonia Resist all strength

hot or cold

Resist all strength hot

or cold

Resist all strength

hot or cold

5 Caustic

Soda

Resist up to 30% hot

or cold slightly

attacked by hot 30-

50% and by molten

salt at 3700C

Resist up to 30-50%

solution slightly

attacked by molten salt

at 3700C

As 18/8

6 Caustic

potash

Resists 25% solution

up to boiling point

Resist 25% solution up

to boiling point slightly

attacked by 50% at

boiling point attacked

by molten salt at 3600C

As 18/8

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MATERIALS FOR CARBAMATE SERVICE

� Carbamate is highly corrosive in nature at high pressure & temperature.

� All over the world licensers of urea plants are searching or cost effective & better corrosion

resistant materials.

MATERIALS FOR CARBAMATE SERVICE

� TITANIUM

� ZIRCONIUM

� 316l MOD OR 316L UG OR 3RE60

� 2RE69 OR 25Cr.-22Ni.-2Mo. (UNS S31050)

� DUPLEX STEEL

TITANIUM

Titanium is used in the relatively pure state .It has excellent corrosion resistance but is one

of the more costly and difficult alloy to weld. Titanium corrosion resistance is due to the

impervious oxide film i.e.100% TiO2 film on surface. Titanium is resistant to stress-

corrosion cracking and erosion corrosion, but it is susceptible to crevice corrosion in

stagnant chloride solutions.

� Used for lining & tube material of ammonia stripper in Snamprogetti’s urea plants.

Commercially pure Titanium exhibits a high resistance to pitting attack.

� Used for lining of urea reactors of TOYO plants MTC Process and corrosion resistance of

Titanium is because of formation of oxide layer In Reactor oxygen is fed with CO2.

ADVANTAGES :

� Passivation air is less required as compared other stainless steel.

� Stripper bottom temperature in Urea Plant can be kept up to 210 0 C while in 2 RE 69

temperature cannot be raised beyond 2070C.

DISADVANTAGES

� Titanium is not maintenance friendly the difficult in welding Titanium is due to high affinity

for Hydrogen, Nitrogen and oxygen in the molten state. Therefore, it must be welded by

such inert-gas welding method as the TIG or MIG process. After a weld has been made, the

inert-gas protection must be maintained until the welding joint cool below 6500C,

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otherwise, the Titanium will react with the oxygen, Nitrogen and moisture in the air,

resulting in weld embrittlement.

� Erosion of tubes ends resulting in bypassing in stripper due to tube end over ferrules badly

eroded by carbamate solution.

Figure No.-6

HCP-(hexagonal closed packed) HCP metal are not ductile as FCC metal

e.g.-Be,Mg,Zn,Cd,Co,Tl,Zr. Etc

The HCP cell consists three layers of atom The top and bottom layers contain six

atom at the corner of the hexagonal and one atom at the centre of each hexagonal.

The middle layer contains three atoms nestled between the atom of the top &

bottom layers hence the name close packed ,figure No-6.

316L MOD & 2 RE 69

These are Tailor made grades of austenitic stainless steel to suit required specifications of

purchaser

USES OF 316L MOD & 2RE69

USES OF 316L MOD & 2RE69

Table No-5

Sr.No. 316 Mod 2 Re 69 1 Reactor Lining Ammonia stripper Lining

2 Carbamate Separator Lining Carbamate Separator Lining & Tubes

3 H.P Section Piping Pool Reactor & Pool Condenser

4 Stamicarbon Reactor Carbamate mixture

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CHEMICAL COMPOSITION 316L MOD & 2 RE 69

Table No.6

Sr.No. Constituents 316LMod 2 RE 69

1 Carbon ≤0.02 ≤0.02

2 Chromium 18 24-26

3 Nickel >13 21-23

4 Molybdenum 2-2.6 2-2.6

5 Manganese 1.5-2 1.5-2

6 Silicon 0.4 0.4

7 Sulphur 0.01 0.015

8 Phosphorus 0.01 0.02

9 Nitrogen(max) 0.10 0.1-0.15

METALLOGRAPHIC PROPERTIES:

� Material in contact with process fluid shall have austenitic structure

� Ferrite content shall not exceed 0.6% except for manual welds, for which 1% is allowed

� “SIGMA PHASE SHALL BE ABSENT”

� Chromium carbides may be present in minimum amount only

� Material shall pass Huey Test & shall be performed according to ASTM A 262 practice ‘C’

and maximum corrosion rate allowed shall be:

Table No.-7

S.No. Type of Material Corrosion rate

mm/yr

Depth of attack

micron

1 316L mod 0.6 90

2 2 RE 69(25/22/2) 0.3 70

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Rate of Corrosion as per Huey Test

Table No-8

S.No. Material Corrosion rate( mm/yr.)

1 ZIRCONIUM 0.005

2 TITANIUM 0.06

3 2 RE 69(25/22/20 0.3

4 316 L MOD 0.6

HUEY TEST-

“Metal sample is boiled in 65% HNO3 for 48 Hrs (5times) to estimate corrosion rate.”

Zirconium

Zirconium is being used in Chemical Industries contains up to 2% Hafnium but does not

affect chemical properties of Zirconium. Zirconium has good mechanical properties at room

temperature, but retains strength at elevated temperatures only if highly

alloyed.Apperance –Steel Grey.

Corrosion resistance because of ZrO2 layer. Zirconium is more expensive than Titanium

(roughly twice that of Titanium)

“DUPLEX” STAINLESS STEEL”

• “DULEX steel is characterized by a microstructure containing both Ferritic phase with a BCC

crystallographic structure and an Austenitic phase with a FCC structure.”

• The Ferritic phase is normally 40-60%, mainly introduced in the wrought alloys by a careful

balance of the critical alloying elements.

• Mixture of Austenite & Ferrite

• Higher strength & better resistance to Chlorides

• Cr: 18-27%, Ni: 4-7%, Mo: 2-4%

• BCC.-Body centered cubic “High strength low ductility.”

• e.g.-Ferrite(α-iron),Cr,V,Mo,W etc.

• FCC-(Body centered cubic). “Low strength high ductility.”

• e.g. Austenite( γ-iron),Al,Cu,Pb,Ag,Au,Ni,Pt etc.

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• Stress Corrosion Cracking

• A particular problem for the common austenitic grades (e.g. 304 and 316) is stress

corrosion cracking (SCC). Like pitting corrosion this occurs in chloride environments, but it

is possible for SCC to take place with only traces of chlorides, so long as the temperature is

over about 60°C, and so long as a tensile stress is present in the steel, which is very

common. The ferritic grades are virtually immune from this form of attack, and the duplex

grades are highly resistant. If SCC is likely to be a problem it would be prudent to specify a

grade from these branches of the stainless family tree.

Advantages of Duplex Stainless Steel

• Good resistance to “chloride stress corrosion cracking.”(CSCC).

• The duplex stainless steel also offers resistance to general and pitting corrosion.

• Good resistance to erosion and abrasion.

• There are numerous cases where plant equipment properly fabricated from duplex SS has

operated with full immunity in chloride containing environment where types 304,304L,

316,316Lhave failed due to stress corrosion cracking.

NEW DEVELOPMENT IN DUPLEX

• First generation duplex.-

The first generation duplex containing.-

Cr-25 %., Ni-5 %, and Mo-1.5 % and Nitrogen ---Nil

There is no Nitrogen. Because Carbon Content up to 0.2%.There is a considerable loss in

corrosion resistance during welding Therefore, a post weld heat treatment is required to

assure good prosperities.

SECOND GENRATION DUPLEX

The second generation duplexes have low carbon levels, assuring resistance to irregular

attack (IGA) the nitrogen contents are usually more than 0.1%.in addition to improving

pitting and crevice corrosion.

Cr. -25 %, Ni.—5 %, Mo.-1.5 %.N- 0.1%.

THIRD GENERATION DUPLEX

• The third generation duplex contains about 0.2% copper.Cr.-25 % Ni.-4.0 % Mo-Nil. Cu.-

0.2%

• “A third generation developed in SWEDON, has recently been introduced Alloy 2304.” and

SAFUREX.

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• HVD-1 is also 3rd generation Duplex S.S. and developed by Snampogetti(Italy).

SUPERFERRITIES

These are highly resistant to chloride pitting and crevice corrosion. They have found extensive

applications as tubing for power plant condensers, and heat exchanger handling chloride solution,

such as Sea water. Having a ferrite microstructure. They have a very high resistance to CSCC. In

addition they are suitable for use in organic acids, dilute reducing acids.

SAFUREX (STAMICARBON)

Safurex is jointly developed by SANDVIK & STAMICARBON and designated SafurexTM.can allow

lower Oxygen content for passivation. Safurex has become a well established material in the Urea

world and has contributed to the improved design, maintenance and operation of urea plants in

many countries. Numbers of H.P. stripper in Stamicarbon plant have been replaced by Safurex.

Chemical composition and PRE No for various Duplex & Stainless Steel

Table No.9

S.No. Grade Cr Ni Mo N PRE Microstructure

1 2RE 60(UG) 18.5 4.9 2.7 0.07 28 Duplex

2 SAF 2304 23 4.5 - 0.1 24 Duplex

3 SAF 2205 22 5.5 3.2 0.18 35 Duplex

4 SAF 2507 25 7 4 0.3 43 Duplex

5 AISI 304L 18.5 10 - - 18 Austenitic

6 AISI 316L 17.5 13 2.1 - 24 Austenitic

7 Sanicro 28 27 31 3.5 - 38 Austenitic

HOW TO GAUGE RESISTANCE TO PITTING

The resistance of a particular grade of stainless steel to pitting and crevice corrosion is indicated by

its Pitting Resistance Equivalent number or PRE, as shown in table. The PRE can be calculated from

the composition as:

PRE = %Cr + 3.3 %Mo + 16 %N

PRE is also known as LCR-Localized Corrosion Resistance

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“Selection for Fabrication”

Again it is usually the case that grades are selected for corrosion resistance and then consideration

is given to how the product can be fabricated. Fabrication should be considered as early as possible

in the grade selection process, as it greatly influences the economics of the product. Table lists

some common grades and compares their relative fabrication characteristics. These comparisons

are on arbitrary 1 to 10 scales, with 10 indicating excellent fabrication by the particular method.

Common Grades and Their Relative Fabrication Characteristics

Table No 10

S.No. Grade

Formability

Machinability

Weldability

1 303 1 8 * 1

2 304 8 5* 8

3 316 8 5* 8

4 416 1 10 1

5 430 4 6 2

6 430 4 6 2

7 2205 5 4 5

8 3CR12 5 6 6

* Improved Machinability versions of these grades offer higher machinabilities in some

products.

A higher PRE value, however, cannot be used as a direct selection criterion. For selection of

material in chloride-containing solution a diagram showing the critical pitting temperature. Has to

be used.

PITTING CORROSION-The pitting resistance equivalent is a simplified way of comparing the

resistance to pitting corrosion for different grade. A higher PRE-value generally means a better

resistance. The PRE-value, however, cannot be used as direct selection criteria. For the selection of

material in chloride containing solution a diagram showing the critical pitting temperature (CPI)

has to be used. As long as the service conditions are below the curve for the considered grade,

pitting will not occur. Figure No. 7 shows the pitting resistance curve for various grades.

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Figure No.-7

REFORMER TUBES

MATERIAL OF CONSTRUCTION :- The Primary reformer is at the heart of any ammonia plant and

represents the largest capital expenditure unit operation and also is the largest energy user on the

plant.As is well known, primary reformer tubes have a finite life and will start to fail after a period

of time. It is therefore usual to replace the reformer tubes at this point and this offers an

opportunity to conduct a fundamental change in the performance of the primary reformer by

changing the metallurgy, inside diameter and thickness of the tubes. When changing the

reformer tubes, there is also an opportunity to re-optimize the catalyst loading to generate

further process benefits. The materials used for the reformer are critical as their performance

directly impacts the technical andeconomic viability of the technology.researchers are

investigateting the behavior of a number of metal and refractory of a number of metal and

refractory material in system that simulates the conditions in a pulse enhance steam reformer.these

test will help to identify those material that perform will in the corrosive,high temperature

environments encountered in the reformer.one of very important aspect to be considered at the

design stage of a reformer,is the materil of construction, as this affects the throughout and the

energy consumption in a fertilser plant.conventianally,the HK40 or IN 519 or equivalmnt material

were being used.

Tube Design Types of tube metallurgy

There has been a great deal of development in the area of tube metallurgy in the last 50 years,

first with the introduction of centrifugally cast tubes in the 1950s,moving through to the

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introduction of HK40 in the early 1960s and then on to the HP modified tubes in the mid-1970s

and finally the HP micro-alloys in the mid-1980’s. The following table illustrates the

development of the metallurgy with time. Metallurgy developments

Table No. –11

Date Common

name

Cr Ni Nb Others Relative

strength

1960s HK 40 25 20 1.0

1970s IN 51 25 24 1 1.4

Mid

1970s

HP mod. 25 35 1 1.9

Mid

1980s

HP micro

alloys

25 35 1 Ti,Zr,W,Cs 2.2

The real key to re-tubes is the significant improvement in strength that can be achieved by

moving to a more modern alloy. The following graph illustrates the maximum allowable stress

data for a variety of materials.

Figure No.-8

The additional strength of modern alloys allows a reduction in the tube wall thickness and a

consequent increase in the reformer tube inside diameter. This in turn leads to significant

reductions in reformer pressure drop and hence plant rate increases. The latest trendis to utilise

micro-alloys,which have a higher creep resistance.These modified HPNb material stablished with

micro-alloys.Typically Chromium-25, Nickel -35%, Niobium -1.5% and, Titanium –Traces. These material have high stability of carbide,increased creep strength, higher durability and

oxidation resistance compared to the conventional material.Tha advantage of using these micro-

alloys are-

0

5

10

15

20

25

30

35

HK40 IN519 HP Nb Mod HP Micro-alloy

Rupture Stress for generic tube

materials(N/mm2)

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1. Possibility of operation of the reformer of higher temperature & pressure.

2. Reduced reformer wall thickness.

3. Increased quality of catalyst packing in the same space-this aspect has been utilised

advantageously, for increasing the capacity of existing reformers.

Tube design principles

To appreciate fully the key aspects of reformer tube management, it is important that the

fundamental principles of the reformer tube design are understood. When designing

reformer tubes, either for a new plant or for a re-tube of an existing primary reformer, the

first key choices are what material, tube thickness and inside diameter will be selected. The

highest value and most critical asset in many plants, the steam reformer, host the components most

likely to experience material failure - reformer tubes. Reformer reliability, availability and

utilization (as measured by reformer tube reliability and condition) affect plant production, outage

risk and potential production loss due to protracted downtime. Plant health, safety and

profitability can be directly improved and unexpected tube failures can be avoided, with confident

predictions of reformer remaining life. However, recognized industry standards for remaining life

evaluation such as API 579-1, do not address reformer tubes. Moreover, the API 579-1 Section 10

Omega method for creep assessment was not designed to consider the unique performance

characteristics of modern HP alloys, which make up most reformer tubes currently in service. The

next stage is to conduct a detailed simulation of the reformer to determine the pressure

and temperature profiles axially along the tube. From this information, the stress being

applied to the tube can be calculated and then, using the allowable stress-temperature data

for the chosen material, the design temperature for the tube can be calculated. This is

Normally illustrated by a Larsen-Miller plot which is a plot of stress against temperature. A typical

Larsen-Miller plot is shown in figure No.9.

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Figure No.-9

If the design temperature is less than the maximum operating temperature, then the design

procedure needs to be repeated with a thicker wall tube; the converse is also true. Since the

Larsen-Miller curves have been generated using a statistical analysis of tubes lives, there will

be some tubes that fail before the expected tube life (typically 100,000 hours). It is normally

expected that 2% of tubes will fail prior to achieving the expected life.

Latest Omega Bond Tubing Technology HP Urea Stripper by M/S Saipem.

Omega Bond® Advanced Tubing -- A Superior Solution to Combat Corrosion

Omega Bond® Tubing is a robust, advanced tubing design for use in corrosive chemical processes

and other applications. Omega Bond® Tubing technology can be applied to the extremely corrosive

urea process. The new tubing designs enable the application of multiple and/or dissimilar metals in

a single tube. Allowing you to put the right alloy where you need it most.

The advantages of this new material technology are a solution to corrosion and erosion issues

observed in urea stripper equipment. Advantages of Omega Bond® Tubing technology includes:

• Superior corrosion resistance of the zirconium inner-liner (zero corrosion rate)

• Directly wieldable into a titanium clad tube sheet without affecting the tube liner bond

strength

• No passivation air requirements

• Useful in existing titanium-tube units

• Eliminates urea solution seepage between the liner and tube because of the extrusion

(metallurgic ally) bonded zirconium inner-liner

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CONCLUSION –Corrosion problems may vary from plant to plant because of local service condition.

When they became frequent, there is a need to select better materials. The initial cost for a better

material may be higher, but a later change to corrosion resistant material is always more expensive.

A number of applications in the production of ammonia, urea and nitric acid have been reviewed

with respect to potential corrosion problem. In many case the cost effective duplex stainless can be

successfully applied in view of past performance.2RE10 is recommended for nitric acid service and

for urea service 2RE 69. The tube metallurgy was upgraded a HP modified micro alloy and this

allowed for an increase in the inside tube diameter. The outside diameter was left unchanged. This

change reduced the pressure drop across the primary reformer by 40% and reduced the natural gas

fuel usage by 3.1%. Both of these effects allowed for an improvement in plant efficiency.

REFERENCES- 19th AFA Int’l Fertilizer Technical Conference & Exhibition18- 20 April 2006 Four

Seasons Hotel Doha- Qatar.

www.alokaloys.com

Fertilizer Industry, 1997 page 115-116, energy bulletin on reformer.U.S. Department of Energy,

Energy Efficiency and renewable energy Sept-2004.

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