Lead seals are small deformable security devices manufactured from pure or low-alloy lead, used for tamper-evident sealing of containers, meters, valves, rail wagons, trucks, and utility equipment.
Their effectiveness relies on lead’s extreme softness and malleability, which allows permanent deformation during crimping—any attempt at tampering becomes immediately visible and irreversible.
Typical Chemical Composition
| Element | Typical Content (%) |
|---|---|
| Lead (Pb) | 99.5 – 99.9 |
| Antimony (Sb) | 0.1 – 0.5 (optional) |
| Tin (Sn) | Trace |
| Copper (Cu) | Trace |
| Bismuth (Bi) | ≤ 0.002 |
Pure lead provides maximum malleability, while small antimony additions improve shape retention and reduce creep.
Key Mechanical Properties
| Property | Typical Value |
|---|---|
| Tensile Strength | 12 – 20 MPa |
| Yield Strength | 5 – 10 MPa |
| Elongation | 35 – 55% |
| Hardness (Brinell) | 5 – 8 HB |
| Elastic Modulus | ~16 GPa |
| Creep Resistance | Low – Moderate |
| Impact Resistance | Excellent |
Low strength is intentional—lead seals must permanently deform during use.
Physical Properties
| Property | Value |
|---|---|
| Density | 11.34 g/cm³ |
| Melting Point | 327.5 °C |
| Thermal Conductivity | ~35 W/m·K |
| Electrical Conductivity | ~4.8 MS/m |
| Corrosion Resistance | Very good |
| Weather Resistance | Excellent |
| Magnetic | Non-magnetic |
Metallurgical & Strengthening Behavior
| Method | Effect |
|---|---|
| Cold Working | Minimal (rapid recovery) |
| Solid Solution (Sb) | Slight hardness increase |
| Heat Treatment | Not applicable |
| Precipitation Hardening | Not possible |
The face-centered cubic (FCC) crystal structure promotes extreme ductility and plastic flow rather than strength.
Key Characteristics
✔ Extremely malleable
✔ Permanent deformation on crimping
✔ Tamper-evident behavior
✔ Weather and corrosion resistant
✔ Easy to emboss or mark
✔ Long outdoor service life
❌ Not reusable
❌ Toxic – regulated handling
❌ Low mechanical strength
Refining & Processing Properties
Manufactured using primary refined lead or high-purity secondary lead under controlled impurity limits.
Typical process flow:
Melting & alloy adjustment
Ingot casting
Die or gravity casting into seal blanks
Punching & hole formation
Embossing (logos, serial numbers)
Inspection & packaging
Fabrication & Workability
| Operation | Suitability |
|---|---|
| Casting | Excellent |
| Stamping | Excellent |
| Embossing | Excellent |
| Machining | Poor (smearing) |
| Welding | Not used |
| Soldering | Possible (rare) |
Available Commercial Forms
Round seals • Flat disc seals • Button seals • Custom-shaped seals • Pre-drilled seals • Seals supplied with steel or copper wire
Typical sizes range from 8 to 15 mm in diameter.
Applications of Lead Seals
Logistics & Transport
Cargo containers, truck doors, rail wagons, shipping bags
Utilities & Infrastructure
Electricity, water, gas meters; telecom cabinets
Industrial & Energy
Valves, fuel tanks, oil & gas equipment
Government & Security
Customs seals, evidence tagging, historical ballot boxes
Advantages
✔ Irreversible tamper evidence
✔ Excellent environmental durability
✔ Easy customization and embossing
✔ Cost-effective security solution
Health, Safety & Regulations
⚠ Lead is toxic and requires PPE, controlled waste disposal, and regulatory compliance.
Permitted for industrial, infrastructure, and security use under REACH, OSHA, and RoHS exemptions.
Why Choose Lead Seals?
Choose lead seals when permanent tamper evidence, environmental durability, custom marking, and cost efficiency are required, and one-time security is acceptable.
Lead seals remain a globally trusted solution due to their irreversible deformation behavior, corrosion resistance, and long-term outdoor reliability.