Eng Standard Practice Metallurgy

1. Table of Contents

1. Table of Contents 1

2. Purpose 2

3. General 2

4. Accountability 2

5. Procedure 2

6. Materials Selection - General 5

6.1 Design Life 5

6.5 Factors Determining Material Selection 5

7. Environmental Considerations 7

7.1 Resistance to Hydrogen Degradation at Operating Temperatures Below 400°F (204°C) 7

7.2 Resistance to Hydrogen Attack at Design Temperatures Above 400°F (204°C) 7

7.3 Resistance to Sulfur 8

7.4 Resistance to Hydrogen Sulfide at Elevated Temperatures 8

7.5 Resistance to Elevated Temperature Oxidation 8

7.6 Resistance to Acids 9

7.7 Postweld Heat Treatment (PWHT) 9

7.8 Radiographic Examination (RT) 10

8. Special Requirements 11

8.1 Mesh Blankets 11

8.2 Valve Trim 11

9. Low Temperature Requirements 12

10. Process Unit Materials of Construction 13

10.1 Piping Materials of Construction 13

10.2 Materials of Construction Other than Carbon Steel for Common Process Units 13

Attachment 1 Average Rate Curves for High Temperature Sulfur Corrosion 20

Attachment 2 – Figure 1 Trend Curves for Predicting Corrosion Rates of 0-5% Chromium Alloy Steel in H2S 21

(Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures 21

Attachment 2 – Figure 2 Trend Curves for Predicting Corrosion Rates of 9% Chromium Alloy Steel in H2S (Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures 22

Attachment 2 – Figure 3 Trend Curves for Predicting Corrosion Rates of 11-13% Chromium Alloy Steel in H2S (Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures 23

Attachment 2 – Figure 4 Trend Curves for Predicting Corrosion Rates of 18% Cr - 8% Ni Alloy Steel in H2S (Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures 24

Attachment 3 Scaling Rate of Some Alloys in Air versus Temperature 25

Attachment 4 Caustic Soda Service Chart 26

Attachment 5 Piping Material Selection Logic 27

2. Purpose

This procedure outlines guidelines for materials selection and sets out special requirements deemed necessary to provide satisfactory service life based on process and metallurgical requirements.

3. General

Materials and special requirements shown on the project specifications will govern if there is a conflict with any Inflection Point Engineering Standard Specification.

4. Accountability

The Design Engineer is accountable for consulting with both the Process Specialist for a specific process and the Metallurgical Specialist to ensure that this procedure is followed.

The Metallurgical Specialist and the Process Specialist shall review the Customer metallurgical requirements to determine acceptability.

5. Procedure

5.1 A Material Selection Diagram (MSD) is required for all Inflection Point Engineering projects, including Revamps where appropriate. A file of “typical” MSDs is maintained within the appropriate Center. These typical MSDs are the accountability of the appropriate Center Leader. Typical MSDs may be used as modules to produce a project specific MSD.

5.2 Work is scheduled between the Project Engineer and the MSD scheduler as far in advance as practicable.

5.3 The Design Engineer will transmit to the Metallurgical Specialist an MSD, which defines and communicates all details of process streams, trace contaminants and alternate operations. The following information must be provided on the MSD:

a. Maximum operating temperatures

b. Equipment design pressures and temperatures including minimum design metal temperature

c. Design H2 partial pressure (Design Pressure x mole fraction H2 in vapor phase)

d. Mole percent H2S in total stream

e. Weight percent or weight ppm S in liquid phase

f. Wet H2S service per NACE MR0103 (Y or N must be indicated for all streams and each piece of equipment – including both shell and tubesides of exchangers). If no equipment is in wet H2S service, apply the following note: “No piping or equipment meets the NACE MR0103 definition of wet H2S service.”

g. CO2 and water partial pressures and dewpoints where applicable (e.g. Selexol, Ecofining, Amine Treating, FCC, etc.)

h. Caustic concentration where applicable

i. For Hydrotreating, Unionfining and Unicracking:

• weight ppm nitrogen in the liquid feed;
• volume percent NH3 in the reactor effluent;
• chloride content of the liquid feed and make-up gas;
• location of ammonium chloride salt deposition, if applicable.

j. For Crude and Vacuum units:

• the total acid number (TAN) of the liquid hydrocarbon streams. This also applies to units where the liquid feed is from a Crude or Vacuum unit.

k. List type and concentrations of any acids used or produced in the process.

l. Amine type and concentration for absorbers and strippers; amine solution loading (mol acid gas/mol amine) for lean and rich solutions

m. For heat exchangers identify all exchangers where the tubes are strength welded to the tube sheet

n. For heat exchangers with multiple exchanger shells (e.g. combined feed exchangers), itemize each exchanger with the information required in 5.3.a-m using the (G:\ESE\Skill Centers\MMESC\Technical\Project Skills & Infrastructure Team\Metallurgy\Metallurgy\ExchangerWorksheet.xls).

o. For process water streams

• Type of cooling water (treated and inhibited, fresh, sea, etc)
• Metallurgy of existing system
• Temperature
• pH
• Total alkalinity as CaCO3, wt ppm
• Oxygen, wt ppm
• Conductivity, micromhos

p. The following information shall be provided with the MSD:

• Customer material requirements
• Customer Design Life requirements, if different from Inflection Point Engineering
• Any applicable Customer/Contractor documents, e.g., Standards, etc.

5.4 When alternate conditions exist for a unit/piece of equipment, such as regeneration, hydrogen stripping, etc., itemize the conditions (5.3.a-m) for each affected piece of equipment in a separate equipment box.

5.5 For REVAMPS: all piping and equipment shall be included on the MSD with all applicable information from 5.3.a-m. Equipment shall have one of three designations labeled at the top of the equipment box:

(1) Existing – for old equipment that is unaffected by new design conditions.

(2) Revamp – for old equipment that is affected by the new design conditions.

(3) New – for new equipment.

5.6 The Heater Specialist shall select the metallurgy for fired heaters. This information is obtained by the Design Engineer and indicated on the MSD.

5.7 Metallurgy for pressure vessels, heat exchangers and piping is selected per IPE-TM-700-02 and indicated on the MSD by the Metallurgical Specialist.

5.8 After the Metallurgical Specialist has completed the MSD mark-up, the MSD is scanned and a link is sent to the Project Engineer, who forwards it to drafting. Drafting then produces the completed MSD. For additional details, see 2069-03, “Material Selection Diagram (MSD) Work Process.“

5.9 After drafting, it is the accountability of the Design Engineer to compare the drafted copy with the marked-up copy and ensure that they match.

5.10 The Design Engineer informs all interested parties of the metallurgy requirements shown on the MSD.

5.11 The Design Engineer is accountable for revising the MSD if any changes are made to conditions outlined in 5.3 a-p. Submit any such changes to the Metallurgical Specialist for re-review.

5.12 The marked-up MSD originals will be filed and maintained by the Metallurgical Specialist.

6. Materials Selection - General

6.1 Design Life

Select equipment construction materials to provide a satisfactory service life for the particular environment encountered, such as:

• 20 year life - high pressure ( 1000 psig) heavy wall reactors, vessels and exchangers

• 10 year life - vessels, exchanger shells, heater coils, pumps and compressor casings and piping

• 5 year life - easily replaced heat exchanger tube bundles and replaceable internals for rotating equipment

Since there are many factors that contribute to the service life of equipment, these target design lives are based on expected operating conditions. In most cases, standard corrosion allowances will provide a service life in excess of these listed.

6.2 Unless requested otherwise by the customer, specify materials by their generic names (e.g. KCS, Type 304, Monel, etc.).

6.3 Where carbon steel is the required material, specify killed carbon steel. Exceptions are tower trays and heat exchanger baffles, where carbon steel is specified.

6.4 Materials conforming to foreign standards equivalent to the ASTM or ASME Specifications are acceptable. Equivalent foreign materials specifications are those that conform to method of manufacture, chemistry, mechanical properties, quality, testing and inspection.

6.5 Factors Determining Material Selection

a. Material Properties

(1) Strength

Materials used to contain process fluids shall have adequate strength at design conditions.

(2) Corrosion Resistance

Materials shall possess sufficient resistance to corrosion or hydrogen attack from the process environment including start-up, shutdown and regeneration.

(3) Toughness

Materials shall possess toughness to resist brittle fracture.

(4) Thermal Shock

Materials must be reasonably resistant to thermal shock caused by rapid process temperature changes.

(5) Abrasion Resistance

In some processes, select materials to provide abrasion resistance from solids in the process stream.

(6) Oxidation

Materials shall possess oxidation resistance if high temperatures in an oxidizing environment are encountered.

(7) Fabrication

Materials shall be compatible with all required fabrication procedures.

b. Design Codes, Standards, and Practices

Materials of construction must comply with code requirements for design, fabrication, inspection and testing. The following are utilized in the :

(1) ASME Section I: Rules for the Construction of Power Boilers

(2) ASME Section VIII, Division 1: Rules for the Construction of Pressure Vessels

(3) ASME Section VIII, Division 2: Rules for the Construction of Pressure Vessels - Alternate Rules

(4) ASME B31.3: Process Piping

(5) ASME B16.5: Pipe Flanges and Flanged Fittings NPS ½ through NPS 24

(6) ASME B16.47: Large diameter steel flanges NPS 26 through NPS 60

(7) Standards of the Tubular Exchanger Manufacturers Association (TEMA)

(8) API Standards and Recommended Practices

(9) NACE Standard Practices and Material Requirements; e.g. MR0103.

(10) ASTM Standards

7. Environmental Considerations

7.1 Resistance to Hydrogen Degradation at Operating Temperatures Below 400°F (204°C)

Specify killed carbon steel for all equipment and piping, except for tower trays and heat exchanger baffles.

7.2 Resistance to Hydrogen Attack at Design Temperatures Above 400°F (204°C)

Resistance to hydrogen attack must be provided for materials, in contact with liquids and vapor containing hydrogen, at elevated temperatures and pressures. Use the latest edition of API Publication 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants”, as a guide for selecting hydrogen resistant materials. Use the following method to utilize this API curve:

a. Determine the hydrogen partial pressure (psia) by multiplying the mole fraction hydrogen in the vapor phase by the absolute DESIGN PRESSURE.

b. The hydrogen partial pressure in a liquid is the same as in the vapor in equilibrium with it. Do not use the mole fraction hydrogen in the liquid for determination of the hydrogen partial pressure. An example where this controls material selection is a Unicracking separator liquid pump and its associated piping.

c. Using the DESIGN TEMPERATURE for the particular equipment, find the point defined by it and the DESIGN HYDROGEN PARTIAL PRESSURE (determined above).

d. The point defined above identifies the minimum metallurgy to resist hydrogen attack. If this point is on a material line, specify the next higher material.

7.3 Resistance to Sulfur

Resistance to elevated temperature sulfur must be provided for materials in contact with sulfur bearing hydrocarbon streams. Determine the corrosion rates in these streams using the graph in Attachment 1, Average Rate Curves for High Temperature Sulfur Corrosion. These curves aid in determining corrosion rates for materials in contact with sulfur bearing hydrocarbon streams and are used primarily for crude, vacuum, visbreaker, asphalt oxidizing units, and raw oil charge lines to hydrotreating, Unionfining and Unicracking units.

In using this curve, use the maximum OPERATING TEMPERATURE of the equipment and select the corresponding corrosion rate for one of the materials listed. Adjust the corrosion rate with a correction factor, taking into account the weight percent sulfur. Note that the reference sulfur level for this curve is 1.0 weight percent.

7.4 Resistance to Hydrogen Sulfide at Elevated Temperatures

For determining materials of construction for process streams handling hydrogen sulfide (H2S) and hydrogen at elevated temperatures, use the curves in Attachment 2, “Trend Curves for Predicting Corrosion Rates”, for steels in H2/H2S environments at elevated temperatures. This includes a family of curves grouped according to alloy content as follows:

Figure 1 0 – 5% Chromium	Figure 2 9% Chromium	Figure 3 11 – 13% Chromium	Figure 4 18% Cr-8% Ni Stainless Steel
Carbon Steel	9 Cr - 1 Mo	Type 405	Type 304
C- 1/2 Mo		Type 410	Type 304L
1 Cr - 1/2 Mo		Type 410S	Type 304H
1 1/4 Cr - 1/2 Mo			Type 316
2 1/4 Cr - 1 Mo			Type 316L
3 Cr - 1 Mo			Type 316H
5 Cr - 1/2 Mo			Type 321
			Type 321H
			Type 347
			Type 347H

In utilizing these curves, use the maximum anticipated OPERATING TEMPERATURE during normal operation and volume percent H2S to determine an anticipated corrosion rate for a particular material.

7.5 Resistance to Elevated Temperature Oxidation

For determining an anticipated metal loss from oxidation, use Attachment 3, Scaling Rates of Some Alloys in Air Versus Temperature. The temperature used is the maximum anticipated OPERATING TEMPERATURE for sustained operation.

7.6 Resistance to Acids

a. Hydrochloric (HCl)

Typically, specify Monel where resistance to HCl (formed during processing) must be provided. Some examples of this are Monel lining in the top of a crude column, Monel mesh blankets in Platforming equipment, and Monel trim valves in streams handling wet Platformer gas.

b. Naphthenic

Where resistance to naphthenic acids is required, use Type 317L.

Typically, use Type 317L in Crude and Vacuum Units processing crude oils that possess total acid numbers (TAN, mg KOH/g Crude) over 0.6, or in areas of high velocity where temperatures range from about 450F (232C) to 750F (399C). The most common areas where Type 317L is employed for naphthenic acid protection is the vacuum column lining from the 450F (232C) zone and hotter, the heavy vacuum gas oil circuit, and the vacuum unit heater coils and transfer piping.

Typically, use Type 317L in units downstream of the Crude and Vacuum Units that possess total acid numbers (TAN, mg KOH/g oil sample) over 1.5, in areas where temperatures range from about 450F (232C) to 750F (399C)

c. Phosphoric (H3P04)

Where resistance to phosphoric acid is required, use Type 316L. Examples of this are in certain areas of catalytic condensation units where phosphoric acid “syrup” is formed.

d. Hydrofluoric (HF)

For resistance to hot HF acid environments and HF acid concentrations below about 60 percent at ambient temperature, use Monel 400. Some examples of this (all in the HF Alkylation Process) are the Acid Regenerator, Polymer Surge Drum and the scrubbing section of the Relief Gas Scrubber.

7.7 Postweld Heat Treatment (PWHT)

Specify post weld heat treatment for killed carbon steel regardless of Code requirements under the following environmental conditions:

a. Hydrogen Sulfide (H2S)

Where the stream meets the definition of wet H2S service as defined by NACE MR0103, paragraph 1.3.5.1.

b. Hydrofluoric Acid

For equipment where the process stream contains any amount of HF acid. (This is not a requirement where seal or strength welding of heat exchanger tubes is performed.)

c. Caustic (NaOH)

Reference Attachment 4, “Caustic Soda Service Chart", to determine if PWHT is required. Use maximum operating temperature and concentration of NaOH (weight percent). Follow the same criteria for KOH. PWHT all equipment and piping in caustic service subject to steamout.

d. Amine

In MEA, DEA or other amines at a concentration greater than 2.0 wt %.

7.8 Radiographic Examination (RT)

RT examination is required for process reasons in addition to construction code requirement in hydrofluoric acid environments:

a. 100 percent radiographic examination is required for the following equipment, due to the high concentration of HF acid. See Inflection Point Engineering Standard Specification 3-11 for additional details.

Acid Mixer	Dump Drum
Acid Settler	HF Stripper
Acid Storage Drum	HF Stripper Feed Settler
Acid Regenerator	Isostripper
Alkylation Reactor	Isostripper Sidecut Receiver
Depropanizer	Liquid Knockout Drum
Depropanizer Feed Settler	Polymer Surge Drum
Depropanizer Receiver

b. Spot radiographic examination is required for all vessels (excluding those listed above) containing any amount of acid.

c. 100% RT is required for 1 Cr – ½ Mo, 1¼ Cr – ½ Mo, 2¼ Cr – 1 Mo and 3 Cr – 1 Mo. See Inflection Point Engineering Standard Specification 3-12 for additional details.

8. Special Requirements

8.1 Mesh Blankets

The standard construction material for vessel mesh blankets is an 18% Cr - 8% Ni stainless steel, usually Type 304. The grid and wire are constructed of the same material as the blanket. Exceptions to the standard material are:

a. Use Monel Mesh Blankets in the Following Environments:

(1) Chloride and HCl

Examples are the top mesh blanket in a vacuum column, product separator mesh blanket in Butamer, Isomar, Penex and Platforming Units and mesh blankets in compressor suction drums handling chloride containing gases.

(2) Hydrofluoric Acid

Mesh blankets in contact with hydrocarbons or gas streams containing HF.

b. Use Type 316 Mesh Blankets in the Following Environments:

(1) Hydrogen sulfide and ammonium bisulfide

An example is the product separator in Unicracking service.

(2) Phosphoric Acid

Examples are in Catalytic condensation units where the presence of phosphoric acid syrup is anticipated.

8.2 Valve Trim

The standard material for valve trim in a killed carbon steel valve is a hardened straight chromium stainless steel, usually 11-13% chromium. Exceptions to the standard valve trim are:

a. Use Monel Trim Valves in the Following Environments:

(1) For all process streams containing any amount of hydrofluoric acid.

(2) For gas streams that meet the wet H2S service definition in NACE MR0103 and chlorides are present greater than 1 ppm.

(3) For cold (less than 400F (204C)) gas streams saturated with water, containing chlorides greater than 1.0 ppm. An example of this is Platforming gas used in a hydrotreating unit.

(4) For valves in sour water streams that meet the wet H2S service definition in NACE MR0103 and chlorides are present in the unit feed streams greater than 0.5 ppm.

(5) For streams where chlorides exceed 0.5 ppm in the feed or 1.0 ppm in the makeup gas.

b. Use Type 316 Trim Valves in the Following Environments:

(1) For gas streams that meet the wet H2S service definition in NACE MR0103 and no chlorides are present.

(2) Where the presence of phosphoric acid syrup is anticipated in a Catalytic condensation Unit.

(3) For valves in sour water streams that meet the wet H2S service definition in NACE MR0103 and no chlorides are present.

c. Use 300 series stainless steels (Types 304 or 316) for valve trim for all carbon steel valves handling hot carbonate solutions in the CO2 removal section of a hydrogen production unit.

d. Valve Trim Substitutes

(1) Hastelloy B-2 or B-3 are acceptable substitutes for Monel trim in hydrofluoric acid service.

(2) Stellite (Cobalt/Chromium/Tungsten Alloy) is an acceptable substitute for Monel trim for valves in all the services described above except hydrofluoric acid.

9. Low Temperature Requirements

9.1 At an MDMT below -20°F (-29°C), killed carbon steel must meet the requirements of ASME Section VIII, Part UCS-66.

9.2 At an MDMT below -55F (-46C), use nickel alloy steels containing 3 1/2% Ni, or austenitic stainless steel; e.g. Type 304.

10. Process Unit Materials of Construction

10.1 Piping Materials of Construction

Attachment 5, "Piping Materials Selection Logistics", provides a step-by-step approach for selecting piping materials of construction and corrosion allowances. This approach considers resistance to hydrogen, combined sulfur and hydrogen sulfide.

10.2 Materials of Construction Other than Carbon Steel for Common Process Units

a. Crude

(1) Use Monel lining in the upper section (usually the top head and shell through tray four) of the crude column for protection against HCl corrosion.

(2) Use Type 405 or Type 410S (11-13 Cr) lining for resistance to high temperature sulfur corrosion. Line the entire bottom section of the crude column, up to a zone where the temperature is approximately 500F (260C). Trays in all lined areas are the same material as the shell lining, i.e., Monel or Type 410.

(3) Crude heater coils are usually 9 Cr - 1 Mo.

(4) Heat exchanger tubes are either Type 410, 5 Cr - 1/2 Mo or 1 1/4 Cr - 1/2 Mo, depending on anticipated corrosion rate.

(5) Piping is usually 5 Cr - 1/2 Mo or carbon steel with corrosion allowances adjusted based on anticipated corrosion rate. Large diameter pipe ( 16 inches diameter) may be specified as carbon steel clad with Type 405 or Type 410S as an alternative to 5 Cr - 1/2 Mo.

(6) When naphthenic acids are a consideration, use Type 317L for the heater coils, heater transfer piping and the crude column lining (the bottom section up to and including the zone where the temperature is approximately 450F (232C)).

b. Vacuum

Use the same approach for materials selection as in crude units; however, do not use Monel in the upper section of the vacuum tower.

When naphthenic acids are a consideration, use Type 317L for the heater coils, heater transfer piping, vacuum column lining (the bottom section up to and including the zone where the temperature is approximately 450F (232°C)), and the heavy vacuum gas oil circuit.

c. Thermal Cracking and Visbreaker

(1) Use the same approach for materials selection as crude units.

(2) Line the residuum stripper and the lower section of the flash fractionator with Type 405 or Type 410S stainless steel.

(3) Piping in the hot areas (usually above 550°F (288°C)) is 5 Cr - 1/2 Mo. Heater transfer piping is 9 Cr - 1 Mo.

d. Fluid Catalytic Cracking

(1) The major considerations for materials selection are corrosion resistance, elevated temperature strength, oxidation and abrasion resistance. Line the majority of areas where abrasion resistance is required with hex-steel and an abrasion resistant lining, e.g. Resco AA-22.

(2) The reactor is typically 1 Cr - 1/2 Mo or 1 1/4 Cr - 1/2, usually lined with Type 405 or Type 410S.

(3) The regenerator is killed carbon steel, internally insulated with 4” or 5” of refractory.

(4) Regenerator cyclones and internals are Type 304 with 0.04% Carbon minimum materials.

(5) The main column is carbon steel in the upper section and typically 1 Cr - 1/2 Mo or 1 1/4 Cr - 1/2 Mo lined with Type 405 or Type 410S in the lower section.

(6) Hot piping around the reactor and regenerator is either Type 304H or 1 1/4 Cr- 1/2 Mo lined with hex-steel and lined or internally insulated (cold wall designed) piping. Slurry piping is 5 Cr - 1/2 Mo.

e. Platforming

(1) The primary concern with selection of construction materials in this unit is resistance to elevated temperature hydrogen.

(2) Reactor heater coils are 9 Cr - 1 Mo.

(3) Reactors are either 1 1/4 Cr - 1/2 Mo or 2 1/4 Cr - 1 Mo, with internals of either Type 321 or Type 347.

(4) The combined feed exchangers are killed carbon steel, or 1 1/4 Cr - 1/2 Mo, depending on resistance to hydrogen. The welded plate exchanger design has Type 321 or Type 304 internal plates.

(5) The hot reactor circuit piping is 1 1/4 Cr - 1/2 Mo or 2 1/4 Cr - 1 Mo.

(6) Mesh blankets, relief valves trim, orifice plates, and thermowells are Monel.

f. CCR

(1) The primary concern with selection of construction materials is resistance to elevated temperature HCl and chlorine.

(2) The Regeneration Tower and associated equipment is Type 316 stainless steel with a 0.04% minimum carbon content.

(3) The air heater and regeneration gas heater are Type 304H.

(4) The venturi scrubber is Hastelloy C-2000 or Alloy 59.

g. Cyclemax

(1) The regeneration tower and associated equipment is Type 316 with the option to use Inconel 600, Incoloy 800 or Type 321.

(2) The air heater and reduction gas heater are Type 304 with 0.04% carbon minimum.

(3) The venturi scrubber is Hastelloy C-2000 or Alloy 59.

h. Hydrotreating, Unionfining and Unicracking

(1) Criteria for materials selection in these units is primarily resistance to elevated temperature hydrogen, sulfur, and hydrogen sulfide. Materials selection is often dependent upon minimizing corrosion products that may plug the reactor bed.

(2) Reactors, hot separators, and flash drums are usually 1 Cr - 1/2 Mo, 1 1/4 Cr - 1/2 Mo, or 2 1/4 Cr - 1 Mo. Reactors are lined with either Type 405/410S or Type 347. Cold separators and flash drums are typically lined with 316L or Monel.

(3) Units with feeds that contain high levels of naphthenic acids (TAN > 1.5) require use of Type 317L material up to and including the lining of the first reactor.

(4) Reactor charge heater coils are usually 9 Cr - 1 Mo or Type 347H.

(5) Combined feed versus effluent exchanger tubes are usually Type 304 (Type 321 when welded to tube sheets), Type 410, 2 1/4 Cr - 1 Mo or 1 1/4 Cr - 1/2 Mo, depending on anticipated corrosion rates.

(6) Reactor circuit piping is 1 1/4 Cr - 1/2 Mo, 2 ¼ Cr – 1 Mo, Type 321 or Type 347.

(7) Reactor effluent air coolers - when an alloy material is required for a Kp of 0.4 or greater, specify Incoloy 825. Kp is the product of mole fraction H2S and mole fraction NH3 in the reactor effluent. When using Incoloy 825, limit velocity to 30 fps.

(8) Mesh blankets in vessels downstream of the reactor circuit are either Monel or Type 316. With heavier charge stocks that contain nitrogen, specify Type 316.

(9) Specify high pressure recycle gas scrubbers using MEA with Type 304L lining. Specify the rich amine piping to the Amine Flash Drum as Type 304L. Other amines may also require lining per the recommendations of the amine supplier.

(10) Product fractionators may be specified to be lined with Type 405 or Type 410S if the anticipated corrosion rate warrants.

(11) For valve trim materials, see section 8.2.

(12) Where the concentration of H2S is greater than 25%, make piping Type 316L. Make vessels KCS clad with Type 316L, or solid 316L.

(13) Where the stripper is steam reboiled, line the top of the column to 150 mm below the top 3 trays with Type 316L. Make the top 3 trays Type 316, all other trays Type 410.

i. Thermal Hydrodealkylation

(1) Material selection is based primarily on elevated temperature strength and resistance to elevated temperature hydrogen.

(2) Reactors are of the cold shell design. They are either 1 Cr - 1/2 Mo or 1 1/4 Cr - 1/2 Mo.

(3) Charge heater coils are Type 347H.

(4) Hot reactor circuit piping is Type 304H.

() The hot combined feed exchanger is constructed primarily of Type 304H.

(6) Incoloy 800H may be used for heater tubes, piping, and exchanger components.

(7) The cold combined feed exchanger is usually 1 Cr - 1/2 Mo or 1 1/4 Cr - 1/2 Mo.

j. HF Alkylation

(1) Use Monel for its resistance to hot hydrofluoric acid in the following equipment:

• Acid regenerator
• Polymer surge drum
• Scrubber section of the relief gas scrubber
• Acid regenerator overhead condenser
• Acid regenerator superheater if isobutane recycle or depropanizer/ HF stripper feed is used as the stripping vapor to the acid regenerator.

(2) Specify all killed carbon steel valves in HF service with Monel trim and other special requirements.

k. Hydrogen Plant

(1) Reformer furnace tubes are centrifugally cast HP modified stainless steel.

(2) The inlet header and pig-tails are 2 1/4 Cr - 1 Mo.

(3) The outlet header and pig-tails are Incoloy 800H.

(4) Base materials for the remaining equipment for resistance to elevated temperature hydrogen is usually 1 Cr - 1/2 Mo, 1 1/4 Cr - 1/2 Mo or 2 1/4 Cr-1

l. Catalytic Condensation

(1) Use Type 316L in this process for resistance to phosphoric acid "syrup".

(2) Specify Type 316L for the following equipment:

(a) Line the effluent rectifier in the bottom area up to the feed point.

(b) Acid knockout drum

(c) Piping from the reactor effluent pressure control valve to the rectifier, and from the effluent rectifier to the acid knockout drum.

m. Amine Treating

(1) Use Type 304L for lining in the top section (from the top head to 6” below tray 5) of the amine stripper.

(2) Use Type 304L for the inlet piping of the amine stripper downstream of the control valve.

(3) Use Type 304 exchanger tubing and baffles; and Type 304L tube sheets in the amine stripper reboiler and the amine reclaimer.

(4) Use either steam jacketed carbon steel or Type 316L for vapor piping leaving the amine stripper receiver.

n. Waste Water Stripping

(1) Contact Condenser Design

• Line the stripper column in the contact condenser area with Type 316L.
• Stripper column trays - Trays 1-7 plus accumulator are Alloy 20. Balance of trays are Type 410.
• Specify the side-cut pump around circuit pump to have an Alloy 20 case and impeller.
• The side-cut pump around cooler is titanium.

(2) Overhead Receiver Design

• The stripper column has Type 316 trays, usually three at the feed point.
• Specify the overhead receiver reflux pump to have an Alloy 20 case and impeller.
• The stripper overhead condenser is titanium.

o. Benfield

(1) Use Type 304L for most of the equipment where both water and CO2 are present.

(2) Line the upper section of the regenerator and absorber with Type 304L.

(3) The rich carbonate solution line is Type 304L from the pressure reducing valve to the solution stripper.

(4) Piping containing lean carbonate solution is carbon steel, except all components smaller than full line size (reducers, valves and line segments) are Type 304L.

(5) Use Type 316L case and impeller for pumps handling streams containing carbonate solution or CO2 and water.

Attachment 1 Average Rate Curves for High Temperature Sulfur Corrosion

Reference Sulfur Level – 1.0 wt%)

Correction Factor	Correction Factor
Wt%	% of Base Rate
<0.02	0%
0.02	5%
0.03	10%
0.06	20%
0.1	30%
0.2	48%
0.3	60%
0.4	67%
0.5	75%
0.6	80%
0.7	85%
0.8	90%
0.9	95%
1	100%
1.2	109%
1.4	115%
1.5	120%
>1.50	120%

Attachment 2 – Figure 1 Trend Curves for Predicting Corrosion Rates of 0-5% Chromium Alloy Steel in H2S

(Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures

Attachment 2 – Figure 2 Trend Curves for Predicting Corrosion Rates of 9% Chromium Alloy Steel in H2S (Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures

Attachment 2 – Figure 3 Trend Curves for Predicting Corrosion Rates of 11-13% Chromium Alloy Steel in H2S (Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures

Attachment 2 – Figure 4 Trend Curves for Predicting Corrosion Rates of 18% Cr - 8% Ni Alloy Steel in H2S (Predominantly Hydrogen + Hydrocarbon) Environments at Elevated Temperatures

Attachment 3 Scaling Rate of Some Alloys in Air versus Temperature

Attachment 4 Caustic Soda Service Chart

Attachment 5 Piping Material Selection Logic

1. Select hydrogen resistant material - use DESIGN temperature and DESIGN hydrogen partial pressure to consult the API Publication 941 Chart. This is the minimum required metallurgy.

2. Using MAXIMUM OPERATING temperature and weight percent sulfur, determine corrosion rate on material selected from the "Average Rate Curves for High Temperature Sulfur Corrosion".

3. Using MAXIMUM OPERATING temperature and volume percent H2S, determine corrosion rate from "Trend Curves for Predicting Corrosion Rates" of 0-5 % Chromium Alloy Steel in H2S Environments at Elevated Temperatures."

4. Compare corrosion rates anticipated from both weight percent sulfur and volume percent H2S.

5. Using the higher of the two rates, choose a metallurgy and corrosion allowance such that the designated design life is met or exceeded.

6. Corrosion allowances for various alloys can be found in Inflection Point Engineering Specification 8-1200.