API MPMS 3.2 2025 PDF

Full title and description

API MPMS CH 3.2:2025 — Standard Practice for Gauging Petroleum and Petroleum Products in Tank Cars. This 2025 edition updates the Manual of Petroleum Measurement Standards (MPMS) guidance on methods, equipment, and procedures for measuring liquid and liquefied-gas contents of railroad tank cars by liquid‑level (gauging) methods, including considerations for vapor‑space measurement and temperature control to improve repeatability and comparability between loading and unloading terminals.

Abstract

This standard specifies a uniform method for measuring liquids and liquefied gases in tank cars using liquid level measurement. It addresses measurement of both vapor space and liquid level, describes gauging and temperature‑measurement equipment used in open and closed systems, and provides procedures intended to reduce variability in custody‑transfer and inventory results.

General information

• Status: Current (in force, 2025 edition).
• Publication date: March 2025 (published March 2025; API lists the 2025 edition).
• Publisher: American Petroleum Institute (API).
• ICS / categories: 75 — Petroleum and related technologies; relevant subcategories include equipment and handling of petroleum products (ICS 75.180 / 75.200).
• Edition / version: 2025 edition (2nd edition / revised MPMS Chapter 3.2, replacing the prior 1995(R2019) version).
• Number of pages: 24 pages (approx.).

Scope

This practice applies to gauging petroleum and petroleum products contained in tank cars by liquid‑level measurement. It covers procedures for obtaining reliable liquid‑level and vapor‑space readings, equipment descriptions for both open and closed measuring systems, and guidance on associated temperature measurement where relevant. The standard is intended for use in inventory and custody‑transfer contexts where tank‑car contents are measured by gauge readings rather than weighing or metering.

Key topics and requirements

• Procedures for liquid‑level (gauge) measurement of tank cars, including ullage/innage methods and required number of readings for reproducibility.
• Measurement and accounting for vapor‑space; guidance on converting or considering vapor space for custody comparisons.
• Descriptions and requirements for gauging equipment (dip tapes, float/tape, servo gauges) and temperature sensors used with gauging operations.
• Calibration, verification and field checks (e.g., gauge tape verification, reference points, bob‑weight/temperature effects).
• Procedures to reduce variability between loading and unloading terminals (standardized measurement steps, documentation and reporting).
• Safety, handling, and basic applicability limitations (e.g., product types and pressure considerations).

Typical use and users

Used by terminal operators, railroad and tank‑car operators, commercial gaugers and inspection companies, custody‑transfer personnel, quality assurance groups, customs/commercial regulators, and trading companies involved in rail transport of petroleum products. API tank‑gauging chapters are commonly referenced by commercial gaugers and regulators for approval and accreditation of gauging services.

Related standards

Closely related MPMS chapters and documents include: API MPMS Chapter 3.1A (Manual Gauging), Chapter 3.1B (Automatic Tank Gauging), Chapter 3.3 (ATG for pressurized tanks), Chapters 4 (Proving Systems), 7 (Temperature Determination), 8 (Sampling), 9 (Density/API gravity determination), and 12 (Calculations for converting level to volume and vapor ↔ liquid corrections). National and international level‑measurement standards (e.g., relevant GB/T/ISO documents for level measurement) may also be used in conjunction with MPMS 3.2.

Keywords

API MPMS, MPMS 3.2, tank car gauging, liquid level measurement, ullage, innage, vapor space, custody transfer, gauge tape, tank car, temperature measurement, commercial gauger.

FAQ

Q: What is this standard?

A: It is API MPMS Chapter 3.2 (2025) — a Manual of Petroleum Measurement Standards practice that defines procedures and equipment for gauging petroleum and petroleum products in railroad tank cars by liquid‑level measurement.

Q: What does it cover?

A: It covers methods for obtaining liquid‑level and vapor‑space measurements in tank cars, equipment descriptions for open and closed gauging systems, temperature measurement considerations, and procedures to improve repeatability and comparability of measurements between terminals.

Q: Who typically uses it?

A: Terminal operators, railroad and tank‑car operators, commercial gaugers and inspectors, custody‑transfer personnel, regulators and customs‑approved gauging services, and companies trading or transporting petroleum by rail. API tank‑gauging chapters are commonly listed in approvals and accreditation guidance for commercial gaugers.

Q: Is it current or superseded?

A: The 2025 edition is current and replaces the prior API MPMS CH 3.2:1995(R2019) version; users should adopt the 2025 text for the most up‑to‑date gauging practice.

Q: Is it part of a series?

A: Yes — it is part of API’s MPMS (Manual of Petroleum Measurement Standards) Chapter 3 (Tank Gauging) and is used together with other MPMS chapters (e.g., 3.1A/3.1B/3.3, Chapters 4, 7, 8, 9, 12, 17) depending on the measurement method and custody‑transfer workflow.

Q: What are the key keywords?

A: Tank car gauging; liquid level measurement; ullage/innage; vapor space; custody transfer; gauge tape; API MPMS; temperature measurement; commercial gauger; tank car.