CHEVRON 800 Materials-Considerations-Heat-Exchanger

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800 Materials Considerations

AbstractThis section provides general background on exchanger materials. It summarizmajor factors that must be considered in selection of materials for exchanger components and in the exchanger design.

Contents Page

810 Major Component Materials 800-2

811 Tubes

812 Tubesheets

813 Baffles

814 Shell

820 Minimum Pressurizing Temperature 800-6

830 Sacrificial Anodes 800-7

840 Insulation 800-7

Chevron Corporation 800-1 December 1989

800 Materials Considerations Heat Exchanger and Cooling Tower Manual

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810 Major Component MaterialsThis section suggests materials for components of shell and tube heat exchangincluding tubes, tubesheets, baffles, and shell. The table at the end of this secti(Figure 800-3) provides a list of ASME materials commonly used for these comnents.

811 Tubes

Tube MaterialThere often is no single correct material for a given service. Although the choictube material is generally dictated by temperature and corrosion conditions, howwell a material performs is greatly influenced by actual service conditions and tcorrosion control measures in use. Keep this in mind when reading Figure 800-which lists common exchanger tube materials. The information is not meant formaterials selection. For information about specific corrosives or specific types oprocess plants refer to the Corrosion Prevention Manual.

Selecting the right tube material is only one way to ensure good performance. Oone can control conditions in the exchanger by altering the nature of the procesfluid or by controlling exchanger design. Also, corrosion-inhibiting chemicals mabe added to the process fluid.

Tube Wall ThicknessTube wall thickness is chosen for temperature-pressure and corrosion considerations. Except at high pressures (usually over 1000 psi) where the strength of thicker tubes is needed, anticipated corrosion rates will determine wall thicknes

The tube thicknesses given below fulfill 95% of typical requirements, although thicker tubes may be used where high corrosion rates are expected. We try to sdardize sizes to simplify maintaining a stock of materials for maintenance.

Effect of Exchanger Design on Corrosion

Maximum Allowable Tube Velocity. In most common hydrocarbon services, exchanger design sets the maximum velocities to accommodate conditions oththan corrosion, such as pressure drop. However, there are some services for wvelocity beyond some critical threshold may initiate rapid corrosion. One exampof this is the “end impingement” failures of copper alloy tubes in sea water. Somother examples are given in Figure 800-2.

Effect of Shell-side Water on Tube Material. In cooling water service, tube life is greatly affected by where the water is put. Cooling water on the shell side creat

Carbon steel tubes: 14 gage minimum (13 gage is average) 12 or even 10 gage is sometimes called for

Alloy tubes: 16 gage (except titanium)

Titanium tubes: 18 or 20 gage

December 1989 800-2 Chevron Corporation

Heat Exchanger and Cooling Tower Manual 800 Materials Considerations

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(1) Inhibited grades only. Use ASTM B111 Grades C44300, C44400.

corrosion problems that may be hard to overcome. For example, in well-treatedcooling water, carbon steel exchanger tubes have good life when the water is tuside. However, it is virtually impossible to obtain good tube life on carbon steel with water on the shell side, no matter how well the water is treated. If one triescompensate by upgrading tube material to Admiralty, for example, a galvanic cosion problem is created where the alloy tubes join the carbon steel baffles. Andthe baffles are upgraded to brass, a new galvanic cell is made where brass baftouch the steel shell.

Shell-side water is also a poor choice for stainless steels. Local boiling may occin low flow areas, especially adjacent to tubesheets, with resultant concentratiochlorides and stress corrosion cracking of the tubes.

Fig. 800-1 Common Exchanger Tube Materials (This table is illustrative only. It is not suitable for materials selec-tion. See Section 811.)

Service Typical Materials Comments

Fresh Water Carbon Steel

Admiralty(1)

304 Stainless Steel

Short life unless water is good quality and chemical treatment is carefully controlled

Very few problems

Only for low chloride waters under nonscaling conditions

Sea Water Admiralty(1)

70—30 Cupro-Nickel

Titanium

Suffers end impingement at high velocity

More resistant to end impingement than Admiralty

Essentially corrosion-proof to 250°F. Special grades OK to 450°F

Hydrocarbons-Sweet Carbon Steel Very sensitive to trace H2S over 500°F

Hydrocarbons-Sour Carbon Steel

5 Chrome—1/2 Moly

Limited to about 550°F maximum

Where too hot for carbon steel

Hydrocarbons-Naphthenic 316 Stainless Steel Above 1.5 neutralization number

Hydrogen-Sweet Carbon Steel, C-1/2 Mo, 1-1/4 CR-1/2 Mo, 2-1/4 CR-1 Mo

Choice depends on temperature and hydrogen partial pressure. See API Publi-cation 941

Hydrogen-Sour Same as above; also 321 Stain-less Steel

Materials choice depends on stainless steel temperature and on hydrogen and H2S partial pressure

Steam Carbon Steel CO2 corrosion may demand better mate-rials in a condensing environment



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Tube Quality and ASTM SpecificationsWhile specifying the proper alloy to get the required corrosion resistance, tube quality is ensured by ordering tubes to the appropriate ASTM specification. An ASTM specification not only covers chemical composition, but also the method tube manufacture and quality control tests. ASTM specifications cover a varietyend uses.

Some of the ASTM specifications commonly used for tubes are:

Except for the carbon steel, all of these specifications cover a number of relatedalloys. For example, B111 covers four kinds of Admiralty, several cupro-nickelsaluminum brass, and aluminum bronze. When specifying materials, cite both thASTM specification and the grade. For example, a welded Type 304 stainless twould be specified as ASTM A240-TP304.

Fig. 800-2 Some Typical Tube Velocity Limits

Service Material Maximum Velocity

Sea Water (Avoid velocities below 3 fps)

Admiralty

70—30 Cupro-Nickel

Titanium

5 fps

6 fps

Effectively no limit

Fresh Water All Materials No hard data available; seldom limits exchanger design

Hydrocarbons All Materials Depends on service but seldom limits exchanger design

Concentrated H2SO4 Carbon Steel 3 fps

Ammonium Bisulfide Solutions (3% +); in wastewater treatment and hydroprocessing plants

Carbon Steel

Stainless Steel,Incoloy 800

Titanium

20 fps in air-cooled exchangers; generally avoid water cooling

30 fps

Effectively no limit;do not use titanium if high-pressure hydrogen is also present

• A179 Seamless carbon steel

• A214 Welded carbon steel

• A199 Chrome-moly steel

• A249 Welded stainless steels

• A213 Seamless stainless steels

• B111 Copper alloys



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Welded vs. Seamless TubesIn general, seamless alloy tubes are ordered instead of welded, but carbon steetubes may be either seamless or welded. With carbon steel, there is little or no fice in life by using welded tubes, and the cost is much lower. However, weldedtubes should be purchased only from Company-approved suppliers who have aproven track record on quality control.

One exception to the above generality is the use of welded titanium tubes; the cdifferential between welded and seamless here is significant, and tube manufacturers have demonstrated their ability to produce defect-free tubing.

812 Tubesheets

MaterialsTubesheets are usually made of the same material as the tubes. One major exction is with copper alloys. General practice is to use naval-rolled brass (NRB) tubesheets with Admiralty tubes and Monel or 70-30 cupro-nickel tubesheets w70-30 cupro-nickel tubes.

CladdingWhen constructing an exchanger using alloy tubes in which the corrosive fluid ithe tubeside, it may be economical to use alloy-clad rather than solid alloy tubesheets. If clad tubesheets are used, cladding thickness should be 0.5 inch,that the first serration is entirely within the cladding. When the tubes are rolled iplace, this will allow an alloy-to-alloy seal at the first serration. Such a seal prevents corrosive fluid from entering the crevice between tube and tubesheet tcause galvanic corrosion where alloy and carbon steel are in contact. See Section 520 and Specification EXH-MS-2583 for more information on cladding.

Galvanic AttackIn places where tubesheet and tube materials differ take the following precautio

• Consider differential thermal expansion that can loosen rolled joints.

• Consider the galvanic relationship between tube and tubesheet when handa corrosive aqueous (i.e., electrically conductive) fluid such as sea water. Dnot use materials that are far apart in the galvanic series, and especially dohave the tubesheet be the more noble metal. (See the Corrosion Prevention Manual, Section 200.)

• Using the wrong materials combination may result in accelerated corrosionend impingement. For example, in sea water service use of a Monel rathernaval brass tubesheet with Admiralty tubes can reduce tube life by an ordemagnitude.

• Know that there are many fluids in which the probability of galvanic attack may not be obvious. The answer here is to search for relevant experience wthat fluid.



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Note that galvanic attack is not a problem in hydrocarbons and usually is not sein fresh water. Galvanic attack can sometimes be prevented through the use official anodes.

Tube RollingThere is no problem in rolling soft tubes into a hard tubesheet. But rolling hard tubes into a soft tubesheet can result in the enlargement of tubesheet holes, withe joint becoming tight. See Section 520 for information on the tube-to-tubeshejoint.

813 BafflesBaffles are usually made of the same material as the exchanger shell, carbon sbeing the most common. The most important consideration in choosing baffle mrial is corrosion resistance; it is poor economy to have to rebuild an exchanger because the baffles have corroded while the tubes are still in good condition. Baffles should be designed to last at least as long as the tubes. One refinery hareplace four expensive titanium bundles after 4 years because the steel carcascorroded.

Seal strips on longitudinal baffles (so-called “lamiflex baffles”) have some speciproblems. They are very thin and have little tolerance for corrosion. In addition,bending stresses render them susceptible to stress corrosion cracking in certaiservices. The 300 Series stainless steels are the most common seal strip matebut special alloys are required for some services such as hydroprocessing planSeek the advice of corrosion or materials engineers before choosing seal strip rials for new services.

814 ShellAn exchanger shell is nothing more than a pressure vessel and is designed according to the same criteria (typically ASME Code, Section VIII, Division 1). Materials suitable for pressure vessels are also acceptable for exchanger shellsimportant materials limitation is that it is seldom practical to use more than 1/4-inch corrosion allowance on an exchanger shell. If corrosion is deeper than thispassing around the baffles will cause a major degradation in exchanger perfor-mance.

820 Minimum Pressurizing TemperatureMinimum pressurizing temperature (minimum design metal temperature) is a crical design factor for pressure vessels. Exchanger shells and channels are presvessels, and must be designed accordingly. This subject is covered in detail in Pressure Vessel Manual.

In brief, we establish a minimum pressurizing temperature to avoid a catastrophbrittle fracture. Ordinary carbon steels, for example, become brittle at low temptures. The ductile-to-brittle transition temperature may range from well above



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ambient to well below ambient, depending on the grade and thickness of steel uA material must be chosen that will not suffer brittle fracture under the conditionin which an exchanger is expected to operate. This includes hydro-test, which mbe done at a temperature above the minimum pressurizing temperature.

830 Sacrificial AnodesThe purpose of sacrificial anodes is to extend the life of critical heat exchanger parts by the application of cathodic protection. The subject is discussed in detaSection 1600 of the Corrosion Prevention Manual.

The Company does not often use cathodic protection for heat exchangers. Althsacrificial anodes can be installed in exchanger channels or water boxes to protubesheets, tube ends, and the channel section itself, anode life usually is not lenough to justify their installation. While such anodes can protect tube ends frocorrosion (as long as the anodes last) protection generally does not extend mothan one or two tube diameters down the inside of the tube.

One application that did prove to be reasonably successful was the installation carbon steel sacrificial anodes in water boxes in the Borco Refinery sea water desalination plant. This was to protect the 90-10 cupro-nickel tubesheets from galvanic corrosion caused by contact with the titanium tubes.

Another successful anode installation was the use of aluminum anodes in exchchannels at Richmond. They prevented galvanic attack of Monel tubesheets caby dissimilar metal contact with titanium tubes in a sea water environment.

840 InsulationHeat exchangers are basically pressure vessels and are insulated as such. Thisubject is covered in the Insulation and Refractory Manual.

The large flanged connections on heat exchangers cause the major problem winsulation. For more information on the criteria for insulating large flanges and tdesign of the flanges and bolting, see Section 550 of this manual.

Removable InsulationRemovable covers can be removed for exchanger maintenance, or to look for fleaks after startup, and then reinstalled after inspection. Large covers, howeverhard to handle, particularly those used on very hot equipment. For design informtion on removable covers, see the Insulation and Refractory Manual, Section 100, and IRM-EG-4197.


800 Materials Considerations

Heat Exchanger and Cooling Tower M

anual

December 1989

800-8Chevron Corporation

Fig. 800-3 Commonly Used Materials for Components of Shell-and-Tube Heat Exchangers (1 of 2)

High Alloy Steels

8Cr-8Ni-3Mo 18Cr-8Ni18Cr-8Ni

Stabilized

A-240-TP316rA-240-TP316L

SA-240-TP304orSA-240-TP304L

SA-240-TP321orSA-240-TP347

A-312-TP316rA-312-TP316Leamless or elded)

SA-312-TP304orSA-312-TP304L(Seamless or welded)

SA-312-TP321orSA-312-TP347(Seamless or welded)

A-182-F316rA-182-F316L

SA-182-F304orSA-182-F304L

SA-182-F321orSA-182-F347

ELDED:A-249-TP316rA-249-TP316LEAMLESS:A-213-TP316rA-213-TP316L

WELDED:SA-249-TP304orSA-249-TP304LSEAMLESS:SA-213-TP304orSA-213-TP304L

WELDED:SA-249-TP321orSA-249-TP347SEAMLESS:SA-213-TP321orSA-213-TP347

Components Carbon Steel

Low Alloy Steels

C-1/2Mo 1-1/4Cr-1/2Mo 2-1/4Cr-1/2Mo 5Cr-1/2Mo 12 Cr 1

PLATES:

(For rolled and welded shells, shell covers, channels and nozzle necks, heads flat covers, tubesheets and baffles)

SA-285-CSA-515 and 516(All grades)

SA-204-ASA-204-B orSA-204-C

SA-387-11Class 1 or 2

SA-387-22Class 1 or 2

SA-387-5Class 1 or 2(Tubesheets and baffles only. Use 12Cr clad for shells and channels.)

Do not use 12Cr for pres-sure containing parts (except tubes). Use 5Cr-1/2Mo tubesheets with 12Cr tubes.

SoS

PIPE:

(For pipe sized shells and nozzle necks)

SA-106-B orSA-53-B

SA-335-P1 SA-335-P11 SA-335-P22 Not used Do not use SoS(Sw

FORGINGS:

(For body and nozzle flanges, blind flanges, couplings and forged flat covers and tubesheets)

SA-105 orSA-181(Class 60 or 70)

SA-182-F1 SA-182-F11 SA-182-F22 SA-182-F5 orSA-182-F5a(For forged tubesheets and covers only)

Do not use SoS

TUBES: WELDED:SA-214SEAMLESS:SA-179

SA-209-T1 SA-199-T11 SA-199-T22 SA-199-T5 SA-268-TP405orSA-258-TP410(Seamless or welded)

WSoSSSoS

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Chevron Corporation800-9

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SA-193-B8 SA-193-B8TorSA-193-B8C

SA-194-8 SA-194-8TSA-194-8C

F

h Alloy Steels

o 18Cr-8Ni18Cr-8Ni

Stabilized

BOLTS:SA-193-B7 SA-193-B7 SA-193-B7 or

SA-193-B16SA-193-B7 orSA-194-B16

SA-193-B5 Do not use SA-193-B8M

Caution: For hydrogen service, verify that Cr and Mo content are high enough to resist H2 attack.

NUTS:SA-194-2H SA-194-2H SA-194-2H SA-194-2H SA-194-3 Do not use SA-194-8M

ig. 800-3 Commonly Used Materials for Components of Shell-and-Tube Heat Exchangers (2 of 2)

Components Carbon Steel

Low Alloy Steels Hig

C-1/2Mo 1-1/4Cr-1/2Mo 2-1/4Cr-1/2Mo 5Cr-1/2Mo 12 Cr 18Cr-8Ni-3M

CHEVRON 800 Materials-Considerations-Heat-Exchanger

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