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P Numbers, F Numbers, and A Numbers in Welding: Comprehensive Guide II 5 FAQs, Quiz & Video


Welding is a critical process in various industries, from construction to manufacturing, where metals are joined together to create sturdy structures and components. To ensure the integrity and safety of welded joints, standardized systems are in place to classify welding procedures and materials. Among these systems, P Numbers, F Numbers, and A Numbers play pivotal roles. In this comprehensive guide, we’ll delve into the significance of these numbers, their applications, and how they contribute to efficient and safe welding practices.

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P Numbers: Decoding Welding Procedures

P Number Definition and Significance

P Numbers, also known as P-IDs (Procedure Identification Numbers), are a part of the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code. These alphanumeric codes provide essential information about qualified welding procedures for specific materials. P Numbers categorize welding procedures based on essential variables, such as base metals, joint designs, and welding processes. These numbers streamline the welding process by offering a clear reference for selecting the appropriate procedure for a particular welding task.

Applications of P Numbers

P Numbers find extensive use in industrial settings where diverse materials need to be joined accurately. When a P Number is assigned to a welding procedure, it signifies that the procedure has been tested and approved for use. This eliminates the need for requalification each time a similar joint is welded, saving time and resources. Industries ranging from oil and gas to aerospace rely on P Numbers to ensure consistency and quality in their welding operations.

F Numbers: Simplifying Filler Metal Selection

Definition and Purpose of F Numbers

F Numbers, or F-IDs (Filler Metal Identification Numbers), are another integral aspect of welding classification. F Numbers provide a standardized system for categorizing filler metals based on their chemical composition, mechanical properties, and usability. This classification assists welders in selecting the appropriate filler metal that complements the base metal and welding process, ensuring a strong and durable welded joint.

Significance in Welding Practices

The compatibility between filler metals and base metals is crucial for achieving a successful weld. F Numbers aid in this compatibility by simplifying the selection process. Welders can refer to a filler metal’s F Number to determine its suitability for a specific application. This streamlined approach reduces the risk of using incompatible filler metals, which could lead to weak welds and compromised structural integrity.

A Numbers: Unveiling Base Metal Groupings

Understanding A Numbers

A Numbers, or A-IDs (Base Metal Group Numbers), are an essential element in welding standards, particularly those set by the American Welding Society (AWS). These numbers define groups of base metals that possess similar weldability characteristics. A Numbers help in assessing the compatibility between different base metals, facilitating efficient and effective welding procedures.

Importance in Welding Selection

When faced with various base metals that need to be joined, welders can turn to A Numbers for guidance. By referencing A Numbers, they can determine which base metals can be welded together without compromising the quality of the joint. This eliminates the need for time-consuming trial and error, resulting in increased productivity and enhanced structural integrity.

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Understanding ASME P Numbers, F Numbers, and A Numbers in Welding

Welding is a complex process that involves joining different materials to create strong and durable structures. To simplify the classification and qualification of welding procedures and materials, the ASME (American Society of Mechanical Engineers) has introduced P Numbers, F Numbers, and A Numbers. These systems play a critical role in ensuring the quality, efficiency, and safety of welding operations. In this article, we’ll dive deeper into each of these numbering systems and their significance in the welding industry.

ASME P-Number System: Categorizing Base Metals

The ASME P-Number system is a part of ASME Section IX, which provides guidelines for welding and brazing qualifications. P Numbers are assigned to specific base materials and alloys, grouping them according to their welding characteristics. This categorization simplifies the welding process by allowing welders to select qualified procedures without repeated testing. Here’s a breakdown of some common base materials and their corresponding P Numbers:

  1. Carbon Steel (C-Mn): P-Number 1
  2. Low Alloy Steel (Cr-Mo Steels): P-Numbers 4, 5A, 5B, 5C, 15E
  3. Stainless Steels (Cr-Ni steels): P-Numbers 8, 10H
  4. Nickel & Ni-base Alloys: P-Numbers 41 to 49
  5. Aluminum & Aluminum Alloys: P-Numbers 21 to 26
  6. Copper & Copper Alloys: P-Numbers 31 to 35
  7. Titanium & Titanium Alloys: P-Numbers 51 to 53
  8. Zirconium & Zirconium Alloys: P-Numbers 61 and 62

ASME F-Number System: Classifying Filler Metals

F Numbers, or Filler Metal Identification Numbers, assist welders in selecting appropriate filler metals based on their composition and properties. This system reduces the need for extensive procedure qualification, as F Numbers are assigned to groups of consumables that exhibit similar welding behavior. Some examples of filler metals and their corresponding F Numbers include:

  1. Carbon Steel: F-Numbers 1 to 6
  2. Low Alloy Steel (Cr-Mo Steels): F-Numbers 1 to 6
  3. Stainless Steels (Cr-Ni steels): F-Numbers 5, 6
  4. Nickel & Ni-base Alloys: F-Numbers 41 to 46
  5. Aluminum & Aluminum Alloys: F-Numbers 21 to 26
  6. Copper & Copper Alloys: F-Numbers 31 to 37
  7. Titanium & Titanium Alloys: F-Numbers 51 to 56
  8. Zirconium & Zirconium Alloys: F-Number 61
  9. Hard-facing Weld Metal Overlays: F-Numbers 71 and 72

ASME A-Number System: Analyzing Weld Metal Composition

The A-Number system assigns numbers to groups of metals and alloys based on their chemical composition for weld metal deposition. This reduces the need for extensive procedure qualifications. However, A-Numbers are specific to the chemical composition of the weld metal, not the raw filler metal. A few examples of materials and their corresponding A Numbers are:

  1. Carbon Steel: A-Number (Not commonly used)
  2. Stainless Steels (Cr-Ni steels): A-Number (Not commonly used)
  3. Nickel & Ni-base Alloys: A-Numbers (Group-specific)
  4. Aluminum & Aluminum Alloys: A-Number (Not commonly used)
  5. Copper & Copper Alloys: A-Numbers (Group-specific)
  6. Titanium & Titanium Alloys: A-Numbers (Group-specific)

In conclusion, the ASME P, F, and A Number systems are indispensable tools in the welding industry. They simplify the selection of welding procedures, filler metals, and ensure that welds meet stringent quality and safety standards. By understanding these numbering systems, welders can achieve efficient and effective welding operations while maintaining consistency and reliability in their work.


Q1: What is the difference between P Numbers, F Numbers, and A Numbers? A1: P Numbers relate to welding procedures for specific materials, F Numbers classify filler metals, and A Numbers group similar base metals for compatibility assessment.

Q2: Can P Numbers change based on welding processes? A2: Yes, P Numbers can vary depending on the welding process, joint design, and other essential variables.

Q3: Are F Numbers universally recognized? A3: F Numbers are widely accepted in the welding industry, especially in countries that adhere to the ASME codes.

Q4: How can A Numbers enhance welding efficiency? A4: A Numbers allow welders to quickly identify compatible base metals, reducing the need for extensive testing and experimentation.

Q5: Do these numbering systems apply to all welding applications? A5: While these numbering systems are widely used, some specialized applications might require additional considerations beyond P, F, and A Numbers.


In the realm of welding, precision and reliability are paramount. P Numbers, F Numbers, and A Numbers provide the necessary structure and classification to ensure consistent and high-quality welding outcomes. By understanding these numbering systems and their applications, welders and industries can streamline their processes, enhance productivity, and guarantee the safety and durability of their welded joints. Whether you’re a seasoned professional or a newcomer to the welding field, a firm grasp of P Numbers, F Numbers, and A Numbers will undoubtedly contribute to your success in the world of welding.

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  6. Material Requisitions 
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P Numbers, F Numbers, and A Numbers: Video details

Attempt Quiz

Question 1:

What is a P Number used for in welding?

Question 2:

What does the F Number represent in welding?

Question 3:

What does the A Number indicate in welding?

Question 4:

Which classification system is commonly used for identifying materials in the ASME Boiler and Pressure Vessel Code?

Question 5:

What is the main benefit of using classification systems like P Numbers, F Numbers, and A Numbers in welding?

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