API STD 650 Vertical Tank Accessories - Nameplate & Grounding Plates

9/27/20253 min read

1. Introduction

In storage tanks constructed under API Standard 650 – Welded Tanks for Oil Storage, in addition to the main structural components (bottom, shell, and roof), certain complementary accessories are required to ensure safe, reliable, and code-compliant operation.

Among these accessories, two elements are of particular importance:

Nameplates, which provide the essential technical information of the tank and ensure traceability throughout its service life.
Grounding lugs, which play a fundamental role in protecting against electrostatic discharges, by integrating the tank into the facility’s grounding system.

Although relatively simple in appearance, both elements are critical for regulatory compliance, operational safety, and installation reliability.

2. Nameplates

2.1 What are they and what are they used for?

Identification plates are permanent metallic plates attached to the tank that contain the essential design, fabrication, and certification data. Their main function is to provide traceability and compliance, acting as the “identity card” of the tank.

2.2 Mandatory information (API 650, Section 10.1.1)

Annex: The applicable Annex (E, F, G, etc.).
Year Completed: The year the tank was completed.
Nominal Diameter: Diameter (m or ft).
Nominal Hight: Shell height (m or ft).
Maximum Capacity: Tank capacity at maximum design liquid level (m³ or bbl). See Figure. 1.
Design Liquid Level: Level or height use for calculation (m or ft).
Design Specific Gravity: Specific gravity used for calculation.
Design Metal Temperature: The lowest temperature consider in the design (Celsius degree or Fahrenheit degrees). See API par. 3.8.
Design Pressure: Which shall be shown as “Atmospheric” unless Annex F and/or Annex V applies (kPa, mm w.c., psi, ich of w.c.). See API 650 par. 10.1.1.i
Maximum Design Temperature: Maximum Temperature used for calculation (Celsius degree or Fahrenheit degrees)
Manufacturer’s Serial No.: Manufacture serial number or Contract number
Stress Relief: Post weld heat treatment (PWHT) conditions. See API 650 par. 10.1.1.n.
Int. Press. Comb. Factor: Ratio of normal operating internal pressure to design internal pressure, with a minimum value of 0.4. See API par. 5.2.2
Purchaser’s Tank No.: Number of the tank.
Ext. Press. Comb. Factor: Ratio of normal operating external pressure to design external pressure, with a minimum value of 0.4. See API par. 5.2.2
Fabricated By: Name of fabricator company
Erected By: Name of erecter company
Shell Course / Material: Show shell rim plate number and material.

Nameplate.

Figure 1

2.3 Location and installation

Typically placed on the lower shell course, near a manhole, or on the reinforcement plate immediately above a manhole.
Must be attached permanently by welding, riveting, bolting, or brazing.
Should be made of corrosion-resistant materials, ensuring legibility throughout the service life of the tank.

2.4 Importance

Provides unambiguous identification of the tank and verification of API 650 compliance.
Serves as an essential reference for inspection, auditing, and maintenance.
Supplies critical design information (capacity, temperature, pressure) during emergencies.

3. Grounding Lugs

3.1 What are they and what are they used for?

Grounding lugs are metal plates welded to the lower shell course, used for the grounding connection of the tank. Their function is to dissipate electrostatic charges, preventing dangerous accumulation that could lead to sparks or ignition during filling, emptying, or mixing operations.

Grounding Lug.

3.2 Minimum quantity required

API 650 establishes that the minimum number must be specified by the Purchaser.
Recommended practice (based on NFPA 77 and API guidelines):
o 2 lugs for small tanks.
o 4 lugs for medium tanks.
o 6 or more lugs for large-diameter tanks.
The final number depends on the tank diameter and the required grounding resistance (usually < 10 ohms).
The suggested maximum lug spacing is 30 m (100 ft)

3.3 Materials and construction details

Made of stainless steel for carbon steel or low carbon steel alloy tanks. If they are attached to other materials lug material shall be similar to the material to which attached.
Typical dimensions:
o Width: 65 mm.
o Length: 100 mm (It can be higher. Add thermal insulation thickness in insulated tanks).
o Thickness: 6 mm.
Equipped with drilled or tapped holes for copper cables or grounding straps.
In carbon steel tanks or low carbon steel alloy tanks it is recommended to install a reinforcement plate between the shell plate and the grounding lug.

3.4 Location and installation

Welded to the lower shell course, near the tank bottom.
Evenly distributed around the circumference.
The connection point must be accessible from outside the tank.

3.5 Importance

Ensure operational safety by preventing electrostatic discharges.
Fulfill electrical and fire safety requirements (API, NFPA).
Provide integration of the tank into the plant-wide grounding system.

4. Conclusions

Nameplates guarantee traceability and regulatory compliance, while grounding lugs ensure electrical and fire safety. Despite their simple nature, both accessories are critical components for the safe and compliant operation of API 650 storage tank