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Materials of Construction - Metals - Lead
June 23, 2003
Introduction
When lead or a lead alloy are used for its
corrosion resistance, the chemical composition or grade is very important and must be
specified. Several specifications for lead
exist worldwide, such as:
| United States |
ASTM B29 Standard Specification for Refined Lead
ASTM B749 Standard Specification for Lead and Lead Alloy Strip,
Sheet and Plate Products
Federal Specification QQ-L-171 |
| Germany |
DIN 17640-1 Lead Alloys for General Purposes |
| United Kingdom |
BS 334 |
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ASTM B29
The American Society for Testing and
Materials recognizes four different grades of lead which differ mostly on the allowable
contents of copper, silver and bismuth. ASTM B29 and B749 are similar in the
classification of the different grades of lead.
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Low Bismuth, Low Silver Pure Lead
Most of the lead produced in the USA is
refined to meet the requirements for this highest purity grade of lead. Used primarily to produce chemicals, this
material assures that products will be free from unwanted impurities.
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Refined
Pure Lead
This grade, like low bismuth, low silver
pure lead, is not so likely to be used for corrosion resistance applications.
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Pure Lead
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Chemical-Copper
Lead
Chemical-Copper lead contains small amounts
of copper which brings to the material improved corrosion resistance and higher mechanical
strength. A small amount of silver further
improves the corrosion resistance in some applications. In the past, chemical lead
and copper-bearing lead were separate specifications having the same copper content.
Copper-bearing lead was basically the same as chemical lead but with lower silver
levels and higher bismuth levels.
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ASTM
B29 Specification
| |
Low Bismuth, Low Silver
Pure Lead |
Refined Pure Lead |
Pure Lead |
Chemical-Copper Lead |
| UNS |
L50006 |
L50021 |
L50049 |
L51121 |
| Lead, min |
99.995 |
99.97 |
99.94 |
99.90 |
| Antimony |
0.0005 max |
0.0005 max |
0.001 max |
0.001 max |
| Arsenic |
0.0005 max |
0.0005 max |
0.001 max |
0.001 max |
| Tin |
0.0005 max |
0.0005 max |
0.001 max |
0.001 max |
| Sb, As and Sn |
- |
- |
0.002 max |
0.002 max |
| Copper |
0.0010 max |
0.0010 max |
0.0015 max |
0.040-0.080 |
| Silver |
0.0010 max |
0.0025 max |
0.005 max |
0.020 max |
| Bismuth |
0.0015 max |
0.025 max |
0.05 max |
0.025 max |
| Zinc |
0.0005 max |
0.0005 max |
0.001 max |
0.001 max |
| Tellurium |
0.0001 max |
0.0001 max |
- |
- |
| Nickel |
0.0002 max |
0.0002 max |
0.001 max |
0.002 max |
| Iron |
0.0002 max |
0.001 max |
0.001 max |
0.002 max |
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DIN 17640-1
DIN 17640-1 defnes four grades of lead as
follows:
| |
Feinblei |
Feinblei |
Hüttenblei |
Kupfer feinblei |
| Werkstoff Nr. |
2.3010 |
2.3020 |
2.3030 |
2.3021 |
| Lead, min |
99.99 |
99.985 |
99.94 |
99.9 |
| Antimony |
0.001 |
0.002 |
0.002 |
0.002 |
| Arsenic |
0.001 |
0.001 |
0.001 |
0.001 |
| Tin |
0.001 |
0.001 |
0.001 |
0.001 |
| Copper |
0.001 |
0.001 |
0.001 |
0.04 - 0.08 |
| Silver |
0.001 |
0.001 |
0.001 |
0.0025 |
| Bismuth |
0.005 |
0.01 |
0.05 |
0.01 |
| Zinc |
0.001 |
0.001 |
0.001 |
0.001 |
| Iron |
0.001 |
0.001 |
0.001 |
0.001 |
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Physical
Properties
| Density |
11341 kg/m³ (708 lb/ft³) |
| Melting Point
|
327.4ºC (621ºF) |
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Mechanical Properties (rolled Chemical Lead)
| Tensile Strength |
1760 psi |
| Elongation |
53% |
| Brinell Hardness |
3.8 |
| Young’s Modulus |
2.0 x 10-6 |
| Creep Strength (2%) |
170 psi |
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Lead Burning
The burning of lead is described in the
Welding Handbook of the American Welding Society. Some
important aspects of lead burning are:
The filler metal has the same melting point
as the lead being burned. Therefore
considerable skill is required to produce an effective joint without burning through or
damaging the lead sheet or pipe. This is why
the use of experienced lead burners is recommended.
Whenever lead is being burned the proper
safety precautions must be followed.
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Testing of Lead Lining
The integrity of a lead lined piece of equipment is important if the lead
lining is going to protect the underlying material. The followng method can be used
to test the integrity of lead lined carbon steel.
The acid wash test is used to detect surface imperfections and penetrating
defects in lead lined equipment. The entire lead lined surface is first cleaned of
oil and grease with a solvent. A dilute (5 to 15%) hydrochloric acid solution is
generously applied to the surface and allowed to dry for 12 to 24 hours. The lead
surface is then washed with water and allowed to dry. Porosity is indicated by a wet
spot. If there are pinholes or cracks that penetrate to the underlying steel, rust
coloured areas will be visible.
An additional indicator used with this method is a solution of potassium
ferricyanide. The indicator is applied after the hydrochloric acid solution has
dried. Prussian blue discolourations will be visible at points where ferricyanide is
in contact with iron salts which are formed where the steel has come into contact with the
acid.
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