Pressure Vessel Systems (1 & 2 l) LEPVS-4600 Series

Head Design

Many of the non-stirred vessels offer a basic head with a 1/8″ NPT plug. These should be considered as only a starting point for custom built vessels as they do not include a safety relief device. Safety codes, good practice, and common sense dictate that a safety relief device should be installed on all vessels. The 1/8″ NPT plug is provided for the user to install their own safety relief device.

Users who take delivery of vessels without safety relief devices installed must take responsibility for installing adequate protective devices before the vessel is placed in service.

Reactors are normally made of Type 316 Stainless Steel, but they can also be made of other alloys as well. The list of available construction materials include:

• Type 316/316L Stainless Steel
• Alloy A-286
• Alloy 20
• Alloy 230
• Alloy 400
• Alloy 600
• Alloy 625
• Alloy B-2/B-3
• Alloy C-276
• Nickel 200
• Titanium Grades 2, 3, 4, & 7
• Zirconium 702 & 705

When special alloy construction is specified for a reactor, the head, cylinder and all internal wetted parts of the vessel will be made of the prescribed material, with the external valves and fittings constructed of stainless steel. Usually the external parts are not subject to the same corrosive conditions which exist inside the vessel, therefore, the higher cost of external parts made of special alloys is seldom justified.

Alloy Designation

Company uses alloy designation numbers to identify the various corrosion resistant alloys available for use in reactors and pressure vessels. These alloys can also be identified by trade names and by ASTM, ASME, DIN and other specification numbers. Many of the high nickel alloys were originally patented and sold under trade names, such as Monel, Inconel, Incoloy, Carpenter Alloy 20, Hastelloy, etc. Most of the original patents have expired and these alloys are now materials of construction available from other reputable suppliers, as well as from the owners of the original trade names.

Among the many corrosion resistant alloys now available, there may be two or three with very similar compositions and intended for use in the same corrosive environment. Each of these alloys has its own physical strength and temperature characteristics as well as its own unique resistance to certain corrosive materials. All of these factors must be considered when making a selection, with cost and availability also becoming factors in the final choice.

• MONEL, INCONEL, and INCOLOY are Registered Trademarks of Special Metals Corp.
• CARPENTER 20 is a Registered Trademark of Carpenter Technology Corporation.
• HASTELLOY is a Registered Trademark of Haynes International, Inc.

The basic composition of these alloys is listed in the table below. Corrosion resistance information can be obtained from various corrosion handbooks and metallurgical publications. Helpful information can also be obtained from the individual alloy manufacturers.

Any abridged listing of corrosion resistance of various metals and alloys can be potentially misleading since it cannot possibly deal with all of the effects of concentration, temperature, pressure and the presence of additional ions, all of which have a significant effect upon the ability of a reactor to withstand corrosion. In addition, the vulnerability of any material to stress corrosion cracking, intergranular corrosion and pitting must also be considered when judging the suitability of a material for a particular application.

The principal characteristics of the several construction materials offered by Company are summarized below. These listings are intended to serve only as a starting point for any study of comparative corrosion resistance and physical properties. Material manufacturer’s booklets on each alloy are available on our website. Additional details may also be obtained from other sources.

Type 316/316L Stainless Steel

Type 316 Stainless Steel is an excellent material for use with most organic systems. A few organic acids and organic halides can, under certain conditions, hydrolyze to form inorganic halogen acids which will attack T316SS. Acetic, formic and other organic acids are routinely handled in T316SS.

T316SS is not normally the material of choice for inorganic acid systems. At ambient temperatures it does offer useful resistance to dilute sulfuric, sulfurous, phosphoric and nitric acids, but sulfuric, phosphoric and nitric acids readily attack T316SS at elevated temperatures and pressures. Halogen acids attack all forms of stainless steel rapidly, even at low temperatures and in dilute solutions.

Although T316SS offers excellent resistance to surface corrosion by caustics, they can cause stress corrosion cracking in stainless pressure vessels. This phenomenon begins to appear at temperatures just above 100 °C and has been the most common cause of corrosion failure in stainless laboratory vessels. T316SS does offer good resistance to ammonia and to most ammonia compounds.

Halogen salts can cause severe pitting in all stainless steels. Chlorides can cause stress corrosion cracking, but many other salt solutions can be handled in stainless vessels, particularly neutral or alkaline salts.

At moderate temperatures and pressures, T316SS can be used with most commercial gases. In scrupulously anhydrous systems, even hydrogen chloride, hydrogen fluoride and chlorine can be used in stainless steel.

Essentially all of the T316SS produced today also meet the specifications for T316L, low carbon stainless steel.

Alloy 20

Alloy 20 is an enriched grade of stainless steel, designed specifically for use with dilute (up to 30 percent by weight) sulfuric acid at elevated temperatures. It can also be used for nitric and phosphoric acid systems as well as for all systems for which T316SS is suitable.

Alloy 400

Alloy 400 is an alloy comprised essentially of two-thirds nickel and one-third copper. For many applications it offers about the same corrosion resistance as nickel, but with higher maximum working pressures and temperatures and at a lower cost because of its greatly improved machinability.

Alloy 400 is widely used for caustic solutions because it is not subject to stress corrosion cracking in most applications. Chloride salts do not cause stress corrosion cracking in Alloy 400. It is also an excellent material for fluorine, hydrogen fluoride and hydrofluoric acid systems. Alloy 400 offers some resistance to hydrochloric and sulfuric acids at modest temperatures and concentrations, but it is seldom the material of choice for these acids. As would be expected from its high copper content, Alloy 400 is rapidly attacked by nitric acid and ammonia systems.

Alloy 600

Alloy 600 is a high nickel alloy offering excellent resistance to caustics and chlorides at high temperatures and high pressures when sulfur compounds are present. In caustic environments, Alloy 600 is unexcelled. It also is often chosen for its high strength at elevated temperatures. Although it can be recommended for a broad range of corrosive conditions, its cost often limits its use to only those applications where its exceptional characteristics are required.

Alloy B-2/B-3

Alloy B-2/B-3 is an alloy, rich in nickel and molybdenum, which has been developed primarily for resistance to reducing acid environments, particularly hydrochloric, sulfuric and phosphoric. Its resistance to these acids in pure forms is unsurpassed, but the presence of ferric and other oxidizing ions in quantities as low as 50 ppm can dramatically degrade the resistance of this alloy.

Alloy C-276

Alloy C-276 is a nickel chromium-molybdenum alloy having perhaps the broadest general corrosion resistance of all commonly used alloys. It was developed initially for use with wet chlorine, but it also offers excellent resistance to strong oxidizers such as cupric and ferric chlorides, and to a variety of chlorine compounds and chlorine contaminated materials. Because of its broad chemical resistance, Alloy C-276 is the second most popular alloy, following T316SS, for vessels used in research and development work.

Nickel 200

Nickel 200 is one of the designations of commercially pure nickel. It offers the ultimate in corrosion resistance to hot caustic environments, but its applications are severely restricted because of its poor machinability and resultant high fabrication costs.

Titanium

Titanium is an excellent material for use with oxidizing agents, such as nitric acid, aqua regia and other mixed acids. It also offers very good resistance to chloride ions. Reducing acids, such as sulfuric and hydrochloric, which have unacceptably high corrosion rates in their pure form can have their corrosion rates in titanium reduced to acceptable levels if relatively small quantities of oxidizing ions, such as cupric, ferric, nickel or even nitric acid are present to act as corrosion inhibitors.

This phenomenon leads to many successful applications for titanium in the hydrometallurgy field where acids, particularly sulfuric acid, are used to leach ores. In these operations, the extracted ions act as corrosion inhibitors.

Prospective users must remember that titanium will burn vigorously in the presence of oxygen at elevated temperatures and pressures. While there have been many successful applications in hydrometallurgy where oxygen and sulfuric acid are handled in titanium equipment, the danger of ignition is always present and must be protected against whenever titanium and oxygen are used together.

Commercially pure titanium is available in several grades. Grade 2 is the material most commonly used for industrial equipment since it can be fabricated by welding and can be used to make vessels compliant to the PED & ASME Codes. Grade 4, which has slightly higher trace levels of iron and oxygen, has higher strength than Grade 2 but it is not suitable for welding and it is not covered by the PED or ASME Codes.

Since most  vessels are not welded, Grade 4 can be used to obtain higher working pressures than can be obtained with Grade 2. Grade 7, containing small amounts of palladium, and Grade 12 containing small amounts of nickel and molybdenum, offer enhanced resistance to certain environments and can be used for reactors and pressure vessels if suitable billets can be obtained.

Zirconium

Zirconium offers excellent resistance to hydrochloric and sulfuric acids however, as with Alloy B-2/B-3, oxidizing ions such as ferric, cupric and fluorides must be avoided. Zirconium also offers good resistance to phosphoric and nitric acids, and to alkaline solutions as well. Two different grades are available: Grade 702 which contains hafnium is the standard commercial grade offering the best resistance to most corrosive agents. Grade 705 contains small amounts of both hafnium and niobium which increases the strength characteristics and allows for higher maximum working pressures for a vessel. Grade 702 typically offers better corrosion resistance than Grade 705. Grade 702 is also more widely available from commercial stocks of raw materials.

High Temperature / High Strength Alloys

In addition to the metals chosen for their corrosion resistance Company also offers some alloys that are selected for their outstanding strength values, their high temperature strengths, or both.

Alloy 230

Alloy 230 is an alloy approved for ASME pressure vessel design for temperatures up to 980 °C. It is an alloy high in nickel, chromium, tungsten, and cobalt. While it has resistance similar to Alloy 600, it is normally selected for its high strengths at very high temperatures. It is sometime selected as a bolting material.

Alloy 625

Alloy 625 is an alloy with chemical resistance similar to Alloy C-276, but with much greater strength. We use this alloy to obtain additional pressure ratings for high temperature applications.

Alloy A-286

Alloy A-286 is an alloy of the Stainless Steel family with very high strengths up to 371 °C. It is commonly used as a bolting material.

Pressure and Temperature Limits

The maximum pressure and temperature at which any reactor or pressure vessel can be used will depend upon the design of the vessel, its material of construction, and other components integral to its design. Since all materials lose strength at elevated temperatures, any pressure rating must be stated in terms of the temperature at which it applies. The listings shown in this catalog show the maximum allowable working pressure (MAWP) for each vessel in pounds per square inch (psi) and in bar at the maximum rated temperature for that particular design when that vessel is constructed of Type 316 Stainless Steel. Maximum pressure and temperature limits for vessels constructed of other alloys are computed and assigned by the Engineering Department in accordance with all applicable regulations.

Lower operating temperatures sometimes permit higher working pressures. For example, the 4560HT High Temperature reactors are rated at 2000 psi (138 bar) maximum pressure and 500 °C maximum temperature. Standard 4560 reactors are rated at 3000 psi (200 bar) maximum pressure at 350 °C maximum temperature.

One should not assume that any vessel being operated at a lower temperature can be used at pressures exceeding the rated MAWP. Factors other than the material strength of the vessel wall may well be the constraint controlling the rating. Other factors that can limit the pressure and temperature ratings are the closures design, the magnetic drive, the type of seal, the choice of other components used, as well as the material of construction.

The maximum operational temperature of some materials is much lower than what is permissible with stainless steel as shown in the table below.

Alloy 20426 °CAlloy 400482 °CAlloy 625 Gr 1648 °C

Multiple factors are involved in safely calculating the maximum working pressures and temperatures of Reactors and Pressure Vessels.

Many optional accessories and fittings are available to customize your pressure vessel to meet and exceed your specifications.

Primary Accessories

• Heaters
• Temperature Controllers
• Gage Block Assemblies
• Coned Pressure Fittings
• Valves and Fittings

Accessories*

• Automated Liquid Sampler
• Liners
• Pressure Hose
• Safety Check Valves
• Liquid Pipettes
• Gas Filling Systems

*May require modifications of vessel to install.

Gaskets & Seals

There are four different types of gasket materials for the main head seal in reactors and pressure vessels, each with its own advantages and limitations. Some of these are recent additions which have significantly expanded the choices a user can consider when selecting a closure and gasket material for the intended operating conditions.

Confined and Contained Flat PTFE Gaskets for Temperatures to 350 °C

The traditional and most popular main head gasket for vessels is a flat gasket made of a PTFE fluoropolymer. In flat gasket closures, the gasket is held in a recess in the vessel cover. The mating lip on the cylinder closes the recess, leaving the gasket completely confined with only a small inside edge exposed to the reactants within the vessel. This combination of complete gasket containment and the exceptional properties of PTFE materials produces a reliable closure for working temperatures up to 350 °C.

Flat contained gaskets require an initial loading pressure in order to develop and to maintain a tight seal. In designs this is produced by tightening a ring of cap screws in a split-ring cover clamp. Fortunately PTFE is slightly “plastic” and will flow under pressure, producing a seal that improves with each use as the gasket is forced into the faces on the head and cylinder. It also is a very forgiving seal which does not require the special care needed to achieve a uniform loading, which is essential when working with a metal or other non-plastic gasket material.

An equally important advantage of the PTFE gaskets is their essentially universal chemical resistance.

Self Sealing O-Rings

Company has greatly expanded its offerings of reactors and vessels which feature self-sealing O-Ring closures. In these designs the sealing force on the gasket is developed from pressure within the vessel itself, eliminating the need for cap screws in the split ring to pre-load the seal. In these self-sealing closures the split ring sections simply lock the head and cylinder together.

Users who select the self sealing O-Ring design must consider two important characteristics of elastometric materials. First, they will not withstand operating temperatures as high as the PTFE gaskets. Secondly, none of these materials offers the universal chemical resistance of PTFE polymers. The chemical resistance is especially important since the O-Ring is directly exposed to the contents of the vessel. Although there are a number of available O-Ring materials, the real choice comes down to two. Fluoroelastomer (FKM) O-Ring, such as Viton, are a first choice for self-sealing closures. They have good chemical resistance and a working temperature up to 225 °C. Perfluoroelastomer (FFKM) O-Ring, such as Kalrez, have extremely broad chemical resistance and can be used at working temperatures up to 275 °C.

Unfortunately, this material should probably be considered an “exotic” because it costs approximately 80 times as much as an FKM O-Ring. And while it will raise the allowable working temperature to 275 °C, as a practical matter, most users intending to work at this temperature level would be well advised to choose a closure with a flat PTFE gasket and a 350 °C temperature limit. Other exotic O-Ring materials are available, and there are economically priced materials such as ethylene-propylene that will resist some materials that cause FKM to fail, with only slight sacrifices in operating temperatures.

Contained Flat Flexible Graphite Gaskets for Temperatures to 600 °C

For operating temperatures above 350 °C, Company uses a flexible form of graphite, called Grafoil®, which has proven to be an excellent high temperature sealing material. It consists of flexible layers of graphite bonded together to produce a gasket that is almost as easy to seal as a flat, PTFE gasket, but with an almost unlimited temperature range and excellent chemical resistance.

Company has converted all of its standard designs to accept a flat, Grafoil gasket whenever operating temperatures above 350 °C are required, replacing the metal gaskets formerly used for high temperatures. These flexible graphite gaskets are held in grooves identical to the ones used for PTFE gaskets and sealed with the same split-ring closures. This makes it possible to substitute a PTFE gasket whenever the vessel is to be used at temperatures below 350 °C. Grafoil gaskets are reusable, but their service life is shorter than can be obtained with a PTFE gasket.

Metal Gaskets

Metal gaskets have traditionally been the only gaskets available for use at temperatures above 350 °C. Company has designs for diamond cross-section metal gaskets which can be furnished for special applications, but we would recommend the flexible graphite gaskets described above for most applications.

Trademarks of Sealing Materials

A number of gasket materials have so dominated their product categories that their Trade Names have become more common than the actual material designation itself. In an attempt to respect the value of these Trade Names and their proper usage and to minimize the disruptions in our descriptions, we have adopted the following generic material descriptions and designations for use in this catalog. Where available we have selected the ASTM material designation.

• Viton®, Kalrez®, and Teflon® are registered trademarks of DuPont Dow Elastomers.
• Grafoil® is a registered trademark of UCAR Carbon Co.Inc.

Pressure Gages

Gages for pressure vessels can be furnished with either 3-1/2 inch or 4-1/2 inch dials in any of the ranges shown in the table below. All have stainless steel Bourdon tubes and 1/4 inch NPT male connections. Alloy 400 gages are available on special order. Accuracy is .5% of full scale for the 4-1/2 inch size and 1 percent for the 3-1/2 inch gages. All standard gages include dual scales, with graduations in both pounds per square inch (psi) and bars. Gages in Pascal units are available on special order. Compound gages which show vacuum to 30 inches of Mercury and positive pressures to 300 psi/20 bar are also available.

When ordering a special gage, specify the gage diameter, the desired range and scale units.

The gage on a pressure vessel should be 150 percent of the maximum operating pressure. This allows the gage to operate in the most accurate pressure range and prevents the gage from being stressed repeatedly to its full range, which will effect the calibration.

Safety Rupture Discs

Pressure Vessels are protected by custom built rupture discs furnished by Fike® Corporation, a specialist in this exotic art. Examination of these discs will indicate that each of these discs is domed. This dome was produced at the factory by taking the individual disc to 70% of its burst pressure.

The ASME as well as other pressure vessel codes dictate that pressure vessels must be equipped with a rupture disc designed to burst no higher than the design pressure of the vessel. For pressure loads that do not cycle rapidly such as our vessels, Fike suggests limiting the actual operating pressure to no more than 90% of its burst pressure. This combination will limit operating pressures to no more than 90% of the design pressure of the vessel.

We have selected Alloy 600 as the standard material for these rupture discs. It provides excellent corrosion resistance while retaining over 90% of its room temperature rating at temperatures up to 450 °C. For added corrosion resistance we can furnish these discs with gold facing or replace with discs made of Alloy C276. Discs can be produced to match any operating pressure and temperature above the stated minimums.

Reactors and pressure vessels from 25 mL to 2000 mL use the 526HC Series Alloy 600 disc or 581HC Series Alloy 600 with gold facing. The 1 gallon and larger use the 708HC Series discs. The 4580 Reactor Systems use the 1415HC Series discs. For a complete listing of part numbers, burst ranges and materials see 231M Safety Rupture Disc Assemblies Operating Instructions.

In general, the 1000 psi disc in the 526HC/581HC Series discs and the 600 psi in the 708HC Series are the lowest available ranges in the Alloy 600 material. Alternate disc materials are available but they do not offer the same corrosion resistant properties and temperature capabilities.

For applications where users prefer a lower range pressure gage, we would add a spring loaded relief valve set to protect the gage and a 1000 psi rupture disc as the fail safe protection.

Users are invited to contact the Technical Support Staff with requirements for special rupture discs.

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