Study on the Influence of Pipeline Steel Standards on Welding Procedure Parameters

In petroleum, natural gas, water transmission, and industrial pressure pipeline projects, many purchasers focus on verifying the steel grade, outside diameter, and wall thickness, but they may overlook one critical issue: different pipeline steel standards directly affect welding procedure parameters.

Although API 5L X52, ASTM A53 Grade B, and ASTM A672 C65 are all carbon steel pipe materials, they may have different requirements for chemical composition control, delivery condition, strength range, impact toughness, and inspection. If the construction contractor directly applies the same welding parameters to all these materials, problems may occur, including heat-affected zone hardening, cold cracking, lack of fusion, reduced impact toughness, or mismatched welded-joint strength.

Therefore, a reliable steel pipe supplier should not provide customers with only specifications and quotations. It should also help customers confirm the material standard, steel grade, carbon equivalent, and welding suitability. With more than 20 years of welded steel pipe manufacturing experience, LONGMA reduces the overall risks associated with steel pipe procurement and field welding through material analysis, welding process control, nondestructive testing, and laboratory verification.

Why Do Material Standards Change Welding Parameters?

Welding is essentially a process of rapid localized heating and cooling. Differences in the chemical composition, wall thickness, strength grade, and original microstructure of a steel pipe result in different microstructural transformations in the heat-affected zone after welding.

The main material factors affecting the welding procedure include:

• Carbon, manganese, and alloying-element content;
• Carbon equivalent and crack sensitivity;
• Steel grade and minimum yield strength;
• Delivery conditions such as normalized, quenched and tempered, or thermomechanically rolled;
• Pipe diameter, wall thickness, and degree of joint restraint;
• Impact test temperature and low-temperature toughness requirements;
• PSL1, PSL2, or additional project-specific technical conditions.

ISO 3183:2019 specifies PSL1 and PSL2 seamless and welded steel pipes used in pipeline transportation systems for the petroleum and natural gas industries, while supplementing the requirements of the 46th edition of API 5L. API released the 47th edition of API Specification 5L in June 2026 and updated several technical areas, including the quality control of high-frequency welded pipe. Therefore, the applicable standard edition must be clearly stated in the purchase contract. It is not sufficient to specify only “API 5L steel pipe.”

Comparison of the Effects of Common Standards on Welding Procedures

ASTM A53/A53M-24 covers welded and seamless black steel pipe and hot-dipped galvanized steel pipe in sizes from NPS 1/8 to NPS 26. ASTM A671 and ASTM A672 are respectively intended for electric-fusion-welded steel pipe used in atmospheric or lower-temperature service and moderate-temperature, high-pressure service. Their application scopes are different, and one standard cannot be substituted for another simply because the pipe dimensions are the same.

1. Carbon Equivalent Determines Preheating and Hydrogen-Cracking Control

Carbon equivalent is one of the key indicators used to evaluate steel weldability. Generally, as the carbon and alloying-element content increases, the heat-affected zone is more likely to develop high-hardness microstructures, and the risk of hydrogen-induced cold cracking also increases.

Ordinary carbon steel with a relatively low carbon equivalent and a small wall thickness generally has a wider welding parameter window. High-strength line pipe, heavy-wall steel pipe, or highly restrained joints may require:

• Increasing the preheating temperature;
• Strictly limiting the diffusible hydrogen content of welding consumables;
• Controlling the interpass temperature;
• Reducing the post-weld cooling rate;
• Extending joint insulation time or implementing the specified post-weld heat treatment.

However, a higher preheating temperature is not always better. Excessive temperatures may enlarge the heat-affected zone, reduce production efficiency, and even impair the local properties of thermomechanically rolled steel. Therefore, the preheating temperature should be determined through welding procedure qualification rather than selected solely from empirical tables.

Purchasers should require suppliers to provide the actual chemical composition in the material certificate and the applicable carbon equivalent data according to the purchase-order standard. Simply stating that a product “complies with X52,” without providing heat-specific chemical analysis, cannot adequately support the design of the field welding procedure.

2. Steel Grade Affects Heat Input and Welding Consumable Strength Matching

As the API 5L steel grade increases from Grade B and X42 to X52, X65, or an even higher grade, the strength, alloy design, and microstructural control method of the material also change.

If welding heat input is too low, insufficient fusion, an excessively rapid cooling rate, and heat-affected zone hardening may occur. If the heat input is too high, it may cause grain coarsening, reduced weld toughness, and heat-affected zone softening in certain high-strength steels.

The selection of welding consumables should not simply follow the principle that “higher strength is safer.” The weld metal must satisfy the design-strength requirements, but excessive overmatching may increase joint hardness and crack sensitivity. For low-temperature pipelines, the impact toughness of both the weld metal and the heat-affected zone must also be considered.

3. Wall Thickness and Pipe Diameter Change the Welding Thermal Cycle

As wall thickness increases, the heat dissipation rate, joint restraint, and number of welding passes also change. Heavy-wall pipelines generally require a higher preheating temperature, stricter interpass temperature management, and a multilayer, multipass welding procedure.

Field girth welds on large-diameter LSAW steel pipes also involve a long bevel circumference, accumulated fit-up deviations, and continuously changing welding positions. If pipe ovality, pipe-end squareness, or bevel dimensions are unstable, uneven root gaps, excessive misalignment, or local lack of fusion may occur at the jobsite even when the welding procedure qualification is acceptable.

Therefore, when purchasing products manufactured according to a pipeline steel standard, the following items should also be checked:

• Pipe-end outside diameter and ovality;
• Negative wall-thickness tolerance;
• Bevel angle and root face;
• Pipe-end squareness;
• Straightness and transportation deformation;
• Whether an allowance has been reserved for field machining.

In the production of round ERW and LSAW steel pipes, LONGMA combines dimensional inspection with weld quality control to help customers improve field fit-up efficiency and reduce welding rework caused by steel pipe dimensional deviations.

4. PSL Level Affects Impact Toughness and Welding Verification

API 5L and ISO 3183 both establish two Product Specification Levels: PSL1 and PSL2. Compared with PSL1, PSL2 generally includes stricter requirements for chemical composition, mechanical properties, carbon equivalent, toughness, traceability, and nondestructive testing. ISO 3183:2019 explicitly covers both Product Specification Levels.

When a project requires PSL2, low-temperature impact performance, or application in a high-consequence area, welding procedure qualification cannot verify tensile strength alone. Charpy V-notch impact specimens may also need to be taken from the weld, fusion line, and heat-affected zone.

This means that welding current, voltage, travel speed, weaving width, and interpass temperature may all become essential variables that require control.

How Does Welding Procedure Qualification Connect Material Standards?

Steel pipe product standards mainly specify how the steel pipe is manufactured and accepted, while field girth welds must also comply with the construction code adopted by the project. ASME BPVC Section IX is used for welding procedure and welder performance qualification. Its core structure includes:

• QW-200 series: Welding procedure qualification and WPS/PQR requirements;
• QW-250 series: Essential variables for different welding processes;
• QW-300 series: Welder performance qualification;
• QW-400 series: Variables relating to base metals, filler metals, electrical characteristics, gases, and welding techniques.

Official ASME information states that Section IX is used for the qualification of welding, brazing, and fusing procedures and personnel, and that it must be used together with the applicable construction code.

A complete set of welding documents usually includes:

1. Welding Procedure Specification: Specifies the range of parameters to be used in the field;
2. Procedure Qualification Record: Records the actual parameters and test results of the qualification test coupon;
3. Welder Qualification Certificate: Demonstrates that the welder can use the specified process to produce an acceptable joint;
4. Base Material and Welding Consumable Certificates: Confirm the traceability of the base metal, electrodes, or welding wire;
5. Inspection Records: Demonstrate that the weld satisfies visual inspection, NDT, and mechanical property requirements.

Purchasers should pay particular attention to one point: an API or ASTM material certificate for the steel pipe does not automatically mean that the field welding procedure has been qualified.

How Does LONGMA’s Internal Laboratory Verify Weld Quality?

Compared with general promotional statements, laboratory test records provide stronger evidence that a supplier truly understands the relationship between welding procedure parameters and material performance.

1. Chemical Composition Analysis

Purpose: Confirm the actual heat-specific chemical composition and evaluate weldability.

Procedure: Verify the heat number, prepare the specimen, perform spectrometric analysis, review the results, and enter the data into the traceability system.

Procurement value: Prevents the preheating and hydrogen-cracking risks from being underestimated when the chemical composition is close to the upper limit permitted by the standard.

2. Tensile and Bend Testing

Purpose: Verify weld strength, ductility, and joint integrity.

Procedure: Take specimens from the specified locations, machine the specimens, perform tensile or guided-bend testing, and record the fracture location and test results.

Procurement value: Confirms that the weld is not merely visually acceptable while lacking adequate mechanical performance.

3. Impact Testing

Purpose: Evaluate the ability of the base metal, weld, and heat-affected zone to resist brittle fracture at the specified temperature.

Procedure: Confirm the notch location, condition the specimen to the required test temperature, perform the impact test, and record the individual and average values.

Procurement value: Particularly important for PSL2 products, cold-region projects, and low-temperature service.

4. Hardness Testing

Hardness testing helps identify abnormal hardening in the heat-affected zone. Excessively high local hardness may indicate an overly rapid cooling rate, insufficient preheating, or improper heat-input control.

5. Nondestructive Testing

The API 5L product standard includes requirements for manufacturing, acceptance, inspection, testing, and product marking. Actual projects must also be executed according to the edition specified in the contract and the project nondestructive testing procedure. The 47th edition, released in 2026, added or revised more than 15 technical areas. Therefore, new orders should confirm whether the customer is using the 46th or 47th edition.

Five Risks Most Commonly Overlooked by Purchasers

First, the standard and steel grade are provided without specifying the standard edition. Different editions may affect manufacturing and inspection requirements.

Second, only the minimum yield strength is reviewed, while the actual chemical composition, carbon equivalent, and delivery condition are not verified.

Third, the steel pipe product certificate is mistakenly treated as a field welding procedure qualification certificate.

Fourth, low-temperature impact testing, additional NDT, or third-party witnessing is requested only after production has been completed.

Fifth, attention is focused only on the unit price, without evaluating hidden costs caused by dimensional deviations, missing documentation, and field welding rework.

A professional API 5L steel pipe supplier should identify these issues during the contract review stage instead of dealing with disputes after the products arrive at the jobsite.

Why Choose LONGMA?

LONGMA has more than 20 years of welded steel pipe manufacturing experience and mainly produces round ERW and LSAW steel pipes. For petroleum and natural gas, water transmission, structural, and industrial pipeline projects, LONGMA can organize production and inspection according to the material standard, steel grade, wall thickness, and service environment.

LONGMA’s advantages include:

• Manufacturing according to API 5L, ISO 3183, and applicable ASTM standards;
• Maintaining traceability of steel plate or strip heat numbers, chemical composition, and mechanical properties;
• Controlling ERW welding heat input, squeeze pressure, and weld heat treatment;
• Controlling the formation and welding parameters of internal and external LSAW welds;
• Providing chemical analysis, tensile testing, impact testing, hardness testing, hydrostatic testing, and NDT capabilities;
• Supporting EN 10204 3.1 documentation and third-party inspection;
• Reviewing supplementary technical conditions before production to reduce the risk of project changes.

Conclusion

Pipeline steel standards not only determine the material grade of the steel pipe but also affect welding heat input, preheating temperature, interpass temperature, welding consumable selection, and post-weld inspection planning. A truly reliable procurement decision should treat the material standard, steel pipe manufacturing, welding procedure qualification, and field construction as one complete system.

As an experienced API 5L steel pipe supplier, LONGMA does not simply provide a quotation. Based on the steel grade, PSL level, dimensions, wall thickness, operating temperature, impact requirements, and inspection scope, we help customers clarify the manufacturing and delivery conditions for their steel pipes.

When submitting an inquiry, purchasers are advised to provide the material standard and edition, steel grade, outside diameter, wall thickness, quantity, length, design temperature, impact requirements, NDT scope, pipe-end configuration, and destination port. Complete technical information enables LONGMA to provide a more accurate manufacturing solution, quality plan, delivery schedule, and commercial quotation.