Temperature Limit for Carbon Steel Pipe Welding

The temperature limit for welding carbon steel pipe is typically controlled between 150°C and 260°C. This range is set to ensure good weld structure and strength, and is closer to the upper limit of interpass temperature or preheating temperature range under certain working conditions. Temperatures that are too high or too low can lead to welding defects and affect weld quality.

In actual engineering, the welding temperature of carbon steel pipes is not a single, fixed value. The temperatures that truly need to be controlled during the welding process mainly include: preheating temperature, interpass temperature, and post-weld heat treatment temperature (if necessary).

The Importance of Temperature for Carbon Steel Pipe Welding

Temperature control is crucial in the welding process of carbon steel pipes. Welding temperature not only affects the weld formation but also directly relates to the weld quality and strength.

A reasonable welding temperature ensures that the metal material is in a suitable state during the welding process, thereby forming a good weld.

General Specifications for Carbon Steel Pipe Welding

CS pipe welding must comply with international or national mandatory standards. Common standards include:

1. Material Matching

The base metal and welding materials must conform to GB/T 5117 (carbon steel welding rods) or AWS A5.1 standards. For example, Q235B steel pipes typically use E4315 welding rods, with a tensile strength ≥430MPa (refer to GB/T 5117-2012).

2. Bevel Design

The V-groove angle is generally 60°±5°, with a blunt edge height of 1.5~2mm and a gap of 2~3mm (ASME B31.3-2022).

3. Preheating Requirements

When the carbon equivalent (Ceq) ≥0.4% or the wall thickness >25mm, the preheating temperature must reach 100~200℃ (GB/T 20801.4-2020).

Temperature Limit for Carbon Steel Pipe Welding

What the temperature to weld carbon steel pipe? The temperatures that need to be controlled during welding mainly include: preheating temperature, interpass temperature, and post-weld heat treatment temperature (if required).

According to industry standards and practical experience, the suitable temperature range for CS pipe welding is usually controlled between 150°C and 260°C, which is closer to the upper limit of the interpass temperature or the preheating temperature range under certain working conditions.

Within this temperature range, the thermoplasticity of the metal material is moderate, preventing overheating that could lead to a loose weld, and also preventing defects such as hydrogen embrittlement or cold cracking due to excessively low temperatures.

Preheating Requirements for Carbon Steel Pipe Welding

1. Preheating Temperature

Generally, the preheating temperature for carbon steel pipeline welding is 100-150°C. 1. Preheating Temperature: Different types of carbon steel pipes require different preheating temperatures:

2. Preheating Time

The preheating time should be adjusted according to factors such as pipe wall thickness and ambient temperature, generally between 20-60 minutes.

3. Preheating Methods

Commonly used preheating methods include flame heating, electric heating, and induction heating. The appropriate method should be selected based on specific circumstances.

4. Preheating Precautions

The preheating temperature, time, and method should be adjusted according to the welding process specifications and should not be changed arbitrarily.

Overheating should be avoided during preheating to prevent affecting welding quality.

The preheating area should be covered with insulation material to ensure the preheating effect.

Interpass Temperature in Carbon Steel Pipe Welding

Interpass temperature refers to the actual temperature of the base material near the weld joint after the previous weld pass is completed and before the next weld pass begins during multi-pass welding.

Based on professional data and practical welding experience, the interpass temperature in the welding process of carbon steel pipelines should be controlled at around 150℃. This temperature range is derived from a comprehensive consideration of various factors, including the melting point and thermal conductivity of the welding materials, as well as heat input and dissipation conditions during welding.

Welding within this temperature range ensures a good metallurgical bond between the weld metal and the base metal, thereby improving the strength and durability of the welded joint.

Post-Weld Heat Treatment Temperature for Carbon Steel Pipes

1. Temperature Range

Post-weld heat treatment of carbon steel pipes typically uses 580-650℃ (refer to ASME B31.3 standard). The specific temperature needs to be adjusted according to the carbon content.

For example, mild steel (C≤0.25%) can use the lower limit (580-600℃), while medium- and high-carbon steel needs to be increased to 620-650℃ to fully eliminate residual stress.

Too low a temperature (<550℃) will result in incomplete stress elimination; too high a temperature (>700℃) may cause grain coarsening, reducing strength.

2. Insulation Time

Calculated based on carbon steel pipe wall thickness, generally 1 hour of insulation is required for every 25mm (GB/T 30583-2014), but the total insulation time must be ≥30 minutes. For example, a 50mm thick pipe requires 2 hours of insulation.

3. Heating and Cooling Rates

The recommended heating rate is ≤220℃/h, and the cooling rate is ≤275℃/h (ASME standard) to avoid cracking due to thermal shock.

Supplementary Requirements for Special Working Conditions

1. Low-Temperature Welding (Below -20℃)

Low-hydrogen welding electrodes must be used, and the preheating temperature should be increased by 20~50℃.

2. Corrosive Media Environment

Post-weld pickling and passivation treatment is required (HG/T 20584-2020).

Factors Affecting Welding Temperature Selection

1. First, the material of the carbon steel pipe. Different materials of carbon steel have different sensitivities to welding temperature.

2. Secondly, the difference in carbon steel pipes schedules is a factor. Pipes with thicker walls require higher welding temperatures to ensure full fusion of the weld.

3. In addition, factors such as the welding environment, welding method, and welding equipment also affect the selection of welding temperature.

Methods for Controlling Welding Temperature

To accurately control the temperature during the welding process, the following measures can be taken:

1. Preheating

Appropriate preheating should be performed before welding, depending on the thickness and type of material. Preheating can reduce the temperature difference of materials during welding, thereby reducing welding stress and the risk of cracking. Interpass temperature control should also be implemented.

2. Using Temperature Control Equipment

The welding temperature can be monitored and adjusted in real time using advanced temperature control equipment, such as thermocouples and temperature controllers.

3. Selecting Appropriate Welding Parameters

Based on the welding materials and process requirements, parameters such as welding current, voltage, and welding speed should be rationally selected to control the welding temperature. Strict adherence to Welding Procedure Qualification (WPS/PQR) is essential.

FAQ

1. Is carbon steel pipe weldable?

Yes. Carbon steel pipes have good weldability, especially low-carbon steel pipes (such as Q235, ASTM A36, ASTM A106 Gr.B, API 5L Gr.B).

2. Is carbon steel pipe hard to weld?

Generally not, but it depends on the material and working conditions.Welding mild steel, thin-walled carbon steel pipes is relatively easy.

When the carbon content is high, the wall thickness is large, or the ambient temperature is low, the welding difficulty increases, requiring preheating and strict control of interpass temperature.

3. Which welding rod is best for carbon steel pipe?

Low-hydrogen carbon steel welding rods are the best choice. Commonly used welding rods include E6013 and E7018 (AWS A5.1).

Summary

In conclusion, limiting the welding temperature of carbon steel pipes is one of the key factors in ensuring welding quality. By reasonably controlling the welding temperature range and making flexible adjustments based on actual conditions, the quality and strength of the weld can be effectively improved, ensuring the safe and reliable operation of carbon steel pipes.