Piping Class and Piping Material Specification: An Overview

What are Piping Classes and Piping Material Specifications (PMS)?

In piping engineering, a Piping Class serves as a systematic category, such as “CS-150,” which defines the design requirements for a specific piping service based on its pressure, temperature, and fluid characteristics. The Piping Material Specification (PMS) is the comprehensive technical document that provides the detailed bill of materials defining the exact components—including material grades, dimensions, standards, and pressure-temperature ratings—required to build a system for that class. A key aspect of this relationship is that a single, master PMS is often developed to support multiple, closely related Piping Classes. For example, a master “PMS-CS-150” document specifying carbon steel components for 150-pound pressure service might be referenced by both the “CS-150-WATER” and “CS-150-AIR” Piping Classes, ensuring standardization while allowing for distinct service applications.

This foundational system is employed across a wide range of industries, including Oil & Gas, Petrochemical, Power Generation, and Pharmaceuticals. In EPC projects, the Piping Class listed on a P&ID and the detailed PMS provide a continuous thread of reference from the FEED and detailed design stages through to procurement, construction, and commissioning. This is especially critical in brownfield modifications, where this system ensures that new piping tie-ins are fully compatible with existing infrastructure, maintaining long-term integrity, compliance, and operational reliability.

Importance of Piping Class and Specification

Why are They Critical?

A Piping Material Specification (PMS) is not just a technical document; it is a foundation for safe and efficient piping system design. Its importance becomes evident in large-scale EPC projects, plant expansions, and brownfield modifications, where multiple stakeholders depend on a single, standardized reference.

Key reasons why PMS is critical include:

Standardizes Piping Components: The PMS maintains uniformity by providing a definitive bill of materials, making procurement, fabrication, and construction smoother and reducing the risk of mismatches.
Improves Safety and Reliability: The Piping Class ensures the design can handle the service conditions, and the PMS ensures every purchased component meets the required pressure-temperature ratings and codes, minimizing leaks and accidents.
Optimizes Costs: This system eliminates over-specification for less demanding services and prevents costly under-specification, striking the right balance between safety, performance, and budget.
Ensures Regulatory and Code Compliance: The development of both is governed by codes like ASME B31.3, guaranteeing adherence and helping avoid compliance failures.
Facilitates Vendor and Contractor Alignment: The Piping Class on a line list and the PMS for procurement provide a clear, uniform reference for all parties, ensuring smooth project execution.

Consequences of Not Having a Proper PMS

Without this structured system, projects are at risk of serious issues such as:

Material mismatches leading to corrosion, leakage, or catastrophic system failure.
Increased downtime due to repair and replacement of incompatible components.
Higher lifecycle costs from maintenance and unplanned shutdowns.
Regulatory non-compliance penalties, delays in project approvals, and potential legal consequences.
Loss of safety and reliability, ultimately increasing the risk to personnel and operations.

Components of Piping Material Specification

A Piping Material Specification (PMS) typically covers all essential details required to select, procure, fabricate, and install piping systems. Each component is carefully defined to ensure compatibility, safety, and compliance with international standards such as ASME, ASTM, and API.

1. Pipe Material & Grade

The PMS specifies pipe material according to process fluid, design pressure, and operating temperature.

Carbon Steel (ASTM A106 Gr. B, A53) → Widely used for general services like water, air, and low-pressure hydrocarbons.
Stainless Steel (ASTM A312 TP304/316) → Suitable for corrosive fluids, chemical services, and high-purity applications.
Alloy Steel (ASTM A335 P11, P22) → Used in high-temperature and high-pressure services, e.g., steam lines in power plants.
Duplex & Super Duplex (UNS S31803, S32750) → Excellent resistance to pitting, chloride stress corrosion cracking, and offshore seawater applications.
Non-metallic (PVC, HDPE, FRP, GRE) → Lightweight, corrosion-resistant solutions for water, drainage, and chemical handling.

2. Pipe Dimensions & Schedule

Standardization of dimensions ensures correct fit-up and pressure containment.

Nominal Pipe Size (NPS) → Defines pipe diameter for design and procurement.
Wall Thickness (Schedules 10, 40, 80, XXS) → Determined by design pressure and corrosion allowance as per ASME B36.10M/B36.19M.
OD (Outer Diameter) & ID (Inner Diameter) → Specified for fabrication accuracy and flow calculations.

3. Flange Specifications

Flanges form a critical part of joining systems and are defined by type, facing, and pressure rating.

Types: Weld Neck, Slip-On, Socket Weld, Blind, Lap Joint.
Pressure Ratings: Class 150, 300, 600, 900, 1500, 2500 (per ASME B16.5).
Facing: Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ) → selected based on pressure and sealing requirements.

4. Valve Specifications

Valves control the flow of process fluids and are specified by type, material, and connection.

Types: Gate, Globe, Ball, Butterfly, Check, Plug.
Material: Cast Iron, Carbon Steel, Stainless Steel, Bronze, or Alloy Steel depending on service.
End Connections: Flanged (ASME B16.5), Threaded (ASME B1.20.1), Butt Weld (ASME B16.25).

5. Fittings & Branch Connections

PMS defines fittings to match the selected pipe material and pressure class.

Fittings: Elbows (90°, 45°), Tees, Reducers (Concentric/Eccentric), Caps, Couplings, Unions.
Branch Connections: Weldolets, Sockolets, Thredolets → used for tapping into main lines while maintaining integrity.
Standards: ASME B16.9 (Butt Weld Fittings), B16.11 (Forged Fittings).

6. Gasket & Bolt Materials

Sealing and bolting are crucial for leak-free operation.

Gaskets: Spiral Wound (metal + filler), Ring Joint (RTJ), Soft Gaskets (PTFE, Graphite).
Bolting Materials: ASTM A193 B7, A320 L7, A194 Grade 2H nuts → chosen based on temperature and pressure service.
Proper gasket-bolt combination prevents blowouts and ensures long-term sealing performance.

7. Insulation & Coating Requirements

Thermal protection and corrosion resistance are part of PMS to ensure longevity.

Thermal Insulation: Calcium Silicate, Mineral Wool, Rockwool, Foam Glass → applied to steam, hot oil, or chilled water lines.
Corrosion Protection: Epoxy coatings, Galvanization, FBE (Fusion Bonded Epoxy), and wrapping systems for buried pipelines.
Fireproofing & Cryogenic Insulation: Specified in specialized services like LNG plants.

Key Parameters in Piping Class Development

When developing a Piping Class, engineers consider the following parameters, which then dictate the contents of the PMS:

Parameter	Description
Design Pressure & Temperature	Defines the maximum operating conditions the system must withstand.
Fluid Characteristics	Determines material compatibility (e.g., corrosive, erosive, toxic).
Environmental Conditions	Influences material selection (e.g., offshore, cryogenic).
Material Availability	Balances technical requirements with project economics (Local vs. imported material costs).
Fabrication Requirements	Considers weldability and necessary heat treatment.
Code Compliance	The governing design code, typically ASME, API, ASTM

Piping Class vs. Piping Specification

This table clarifies the distinct roles of these two interconnected concepts.

Feature	Piping Class	Piping Specification (PMS)
Nature	A concept/category (e.g., CS-150).	A detailed, executable document.
Purpose	To categorize systems with similar design conditions and fluid service.	To specify the exact components, standards, and fabrication methods for that class.
Content	Service fluid, P-T rating, material group, corrosion allowance.	Bill of Materials (BOM), component standards, testing procedures.
Primary Users	Process Engineers, Piping Engineers.	Piping Designers, Procurement, Fabricators, Construction.

Steps to Develop a Piping Material Specification

Developing a Piping Material Specification is a methodical process that translates process requirements into a technical procurement and fabrication document. It typically follows these key stages;

Define Fluid Service & Operating Conditions: Identify the process fluid, design pressure, and temperature.
Establish the Piping Class: Create a class designation (e.g., “SS-300-COR”) that encapsulates the service requirements.
Select Suitable Material: Based on the class, choose the base material for corrosion resistance and strength.
Determine Pipe Size & Wall Thickness: Perform code calculations (ASME B31.3) to establish pressure integrity.
Develop the PMS: Create the document detailing all components—flanges, fittings, valves, gaskets, and bolts.
Include Testing & Inspection Requirements: Specify hydrotest pressure, NDT methods, and material verification (PMI).
Review & Approve: Validate the Piping Class and PMS with process, mechanical, and QA/QC teams.

Best Practices for Piping Material Specification

Use Industry Standards (ASME, API, ASTM).
Conduct Material Compatibility Studies.
Involve Cross-Functional Teams (Engineers, Procurement, Fabricators).
Regularly Update PMS based on operational feedback.
Perform Failure Mode Analysis (FMEA) for critical services.

Conclusion

Piping Material Specification (PMS) is the backbone of safe and efficient piping systems. By following standardized practices, engineers can ensure reliability, compliance, and cost-effectiveness in industrial projects. Whether designing a new plant or upgrading an existing system, a well-drafted PMS minimizes risks and enhances operational longevity.