I/EC
Materials of Construction
Shielding Against Corrosives a n d Radioactivity by Alfred
P. Knapp, Knapp Mills Inc.
Lead-surfaced Insmetals combine g o o d structural properties w i t h resistance to radiation a n d corrosion
INSMETALS (International Shielding Metals) are a new family of metals, yet about 50,000 tons of prototypes has already been fabricated. Except for one, Inslead which is lead alone, they are lead-surfaced metals and combine the excellent gamma-shielding as well as corrosion-resistant properties of lead with those of the metal (called the base metal) on which the lead surface is applied. Insmetals are fundamental mediums for designers, engineers, and chemists to consider for equipment throughout the chemical process industries. Where Insmetals are used in conventional chemical process equipment, the lead-surfaced face of the metal is intended to withstand the
Nicrolum heating and cooling coil. less steel and the outside is l e a d
corrosive conditions. Where radioactive corrosion is involved, the lead surface has high gamma-shielding value, and, depending on the corrosive, it may have good corrosion resistance as well. In those instances where lead is not correct from a corrosion viewpoint, the opposite side of the metal can be faced toward the corrosive. However, regardless of whether corrosion only or radioactive corrosion is involved, performance data of lead under various operating conditions are important to consider in establishing whether or not Insmetals are basically the best material. E q u i p m e n t Costs
T h e following discussion covers Ferrolum process equipment and piping, and Cupralum heating and cooling coils or heat exchangers; these are the two metals preferred for chemical process equipment. T h e initial cost of Ferrolum equip-
The inside is stain-
ment usually is lower than stainless steel, glass-lined equipment, corrosion-resisting nickel or copper alloys, high silicon iron, or sheet-lead linings if supported or protected by brick. Likewise initial cost of Cupralum heating and or cooling coils or heat exchangers usually is lower than stainless steel, high silicon iron, corrosion-resisting nickel, copper alloys, or Karbate. Where high steam pressures are available, Cupralum can have a lower initial cost than even ordinary lead pipe, because the footage needed for heating in such cases is appreciably less. This is because Cupralum can withstand high steam pressure (150 to 200 p.s.i. standard wall), whereas lead pipe normally is not considered, except at relatively low steam pressures. Installation cost of both Ferrolum and Cupralum may be less, but never more than comparable mediums. Maintenance is practical,
S h i p p i n g cask f o r spent nuclear f u e l is m a d e o f F e r r o - N i c r o l u m . Its w a l l s a r e a f o o t thick VOL. 53, NO. 3
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MATERIALS OF
CONSTRUCTION
These are the Insmetals BAUXILUM. Comparatively new to the chemical industry, but receiving increasing consideration in the nuclear industry. Base metal, aluminum and its alloys. CUPRALUM. Used increasingly in chemical industry but relatively new in nuclear industry. Base metal, copper and its alloys. INSLEAD. Oldest and yet newest of the group. Has been used in chemical industry for centuries, but use in the nuclear industry presents new possibilities. Product is solid lead without base metal.
and simple, reliable techniques are provided to users. The lead surfaces do not require burner's techniques—by using a patented walking mold, repairs are easily made, even in an upright position. Where a leak occurs in Ferrolum equipment, it penetrates the lead surface to the outside steel surface, and may be repaired from the outside of the equipment if necessary. The metallurgical bond between the lead and steel surfaces prevents corrosive liquor from penetrating between the two metals. Often, after years of service, a flame-washing treatment may be used to reprocess, a n d / o r increase, if necessary, the thickness of the lead surface of Ferrolum. For practical purposes such flame-washed vessels are in as-new condition. Cupralum also may be readily repaired or reprocessed by simple techniques. Cost of Ferrolum and Cupralum, related to production losses caused by failure of equipment, is minimized by three factors: 1. The entire thickness of the lead surface is available for corrosion protection. Strength is provided by the opposite steel or copper surface. The lead thickness, generally 3 /ic, y 4 , and 3/s inch or more, usually is greater than the thickness provided by competing metals for corrosion protection only.
2. The lead surface readily lends itself to simple inspection. The development of possible areas needing attention after service can easily be determined in advance. These areas may be treated long before they represent a source of trouble. Periodic shutdown and inspection, 76 A
FERROLUM. Except for Inslead, has received widest attention in both chemical and nuclear industries. Base metal, carbon steel. NICROLUM. Used widely in nuclear industry and being considered by chemical industry. Base metal, stainless steel or other nickel < "oys. FERRO-NICROLUM. Becoming a standard gamma shield in nuclear industry, and being introduced in the chemical industry. Base metal, stainless clad carbon steel.
as part of good, normal plant maintenance, therefore is indicated. II equipment does leak in service, the repair may be made in prompt and simple fashion, often without shutdown. 3. Probability of shutdowns also is related to how the metal or materials selected will withstand operating and corrosive conditions involved. Under conditions such as thermal cycling, pressure, vibration, shock, or vacuum, Ferrolum compares with steel and Cupralum with copper. Temperature Limits
Temperature limits for Insmetals are related to two factors: 1. The metallurgical bond between lead and steel or copper can withstand temperatures up to the melting point of lead itself—i.e., 621° F. 2. Corrosive value of lead with a given corrosive at a given temperature. Much data has been gathered on corrosion of the lead surface of these metals under various conditions for the chemical process industries in the United States, Canada, Great Britain, France, Germany, and Italy. The metals have wide utility. Corrosives against which they have established good to excellent resistance include sulfuric acid, chromic acid, phosphoric acid, aluminum sulfate, ammonium sulfate, copper sulfate, ferric sulfate, barium sulfide, hydrogen sulfide, ammonium sulfite, calcium bisulfite, potassium bisulfite and metabisulfite, sodium bisulfite, bromine, chlorine dioxide, aniline dyes, some concentrations of hydro-
INDUSTRIAL AND ENGINEERING CHEMISTRY
chloric and hydrofluoric acid, and nitrocellulose. Lead Thickness
Corrosion value of the lead surface results from a protective, tenacious film which forms on the surface in contact with the corrosive. If the usual thickness of the lead surface is insufficient, it can be made heavier at only slightly increased cost— lead is inexpensive, and manufacturing costs are not importantly affected by greater thicknesses. Where velocity, abrasion, erosion, or severe vibration may repeatedly remove these protective coatings, heavier surfaces are desirable. Also, the protective film may be preserved by a suitable brick liner or other membrane installed over the surface. Selecting Materials
Where lead has a good corrosion value with a given chemical and process temperature, equipment made with Insmetals is usually cheaper. When the corrosive is radioactive, these metals are especially desirable and lowest in cost. And, if the radioactive corrosive attacks lead, the base-metal side can face the corrosive with the lead side acting as a gamma shield. Such equipment may cost less than other design approaches.
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