Temperature Range of Carbon Steel Pressure Piping

According to ASME B31.3 "Process Piping" and ASTM A106/A53 material standards, the temperature range of carbon steel pressure piping is not a fixed value, but is determined by the material's minimum design metallographic temperature (MDMT) and high-temperature creep limit.

1. High-Temperature Limit

◆ General Upper Limit for Carbon Steel Pipes: 

For the most commonly used carbon steel pipes such as ASTM A106 Gr.B or A53 Gr.B, the maximum permissible operating temperature is set at 425°C in ASME B31.3.

◆ Core Risks—Creep and Graphitization:
Below 425°C: The material has reliable tensile strength and yield strength, and design calculations are performed based on elastic theory.
Above 425°C: The material enters the creep region (i.e., it will continue to deform slowly under constant stress). Simultaneously, long-term use will lead to graphitization (the decomposition of carbides in pearlite into free graphite), resulting in severe embrittlement of the material.

◆ Short-term exceptions:
Under special operating conditions, ASTM A106 Gr.B is permitted for transient use up to 480°C, but this requires very strict control of the service time and is usually accompanied by extremely low allowable stress.

2. Low-temperature limit

Carbon steel loses its toughness at low temperatures, becoming as brittle as glass. The American standard system does not directly specify an absolute low-temperature value, but rather uses the MDMT concept, mandating impact testing for verification.

◆ General default lower limit: -29°C
According to the "exemption curve" in ASME B31.3 and ASTM standards, when the thickness is ≤ 50mm and no low-temperature impact test is performed, the minimum service temperature of A106 Gr.B is generally considered to be -29°C. This is the lowest safe temperature for ordinary carbon steel.

◆ Forced Impact Temperature: Below -29°C
If the design temperature is below -29°C, or the wall thickness exceeds the thickness specified in the exemption curve, a Charpy V-notch impact test (CVN) must be performed at the expected lowest temperature according to ASME B31.3.

◆ Optional Alternative: -46°C
If the impact energy of A106 Gr.B does not meet the requirements at -46°C (or if you do not want to take this risk), the material must be replaced directly. For example, ASTM A333 Gr.6 (-46°C low-temperature carbon steel) can be selected, which is specifically designed for low-temperature environments.

Comparison of Commonly Used Carbon Steel Materials in US Standards:

Material Grade	Temperature Range	Characteristics and Limitations
A106 Gr.B / A53 Gr.B	-29°C to 425°C	Standard general-purpose carbon steel for industrial piping, with excellent cost performance. Impact testing is required below -29°C; use is strictly prohibited above 425°C.
A106 Gr.B (after impact verification)	-46°C to 425°C	Requires impact testing at -46°C, and the material must be smelted using a "fine-grained" process. However, this is rarely used in practice due to its high risk.
A333 Gr.6	-46°C to 343°C	Low-temperature carbon steel. This is the standard solution for -46°C conditions, requiring no impact testing, but it is more expensive than A106.
API 5L Gr.B	-20°C to 400°C	Linear conduit standard. While also used for transportation, its high-temperature stability is worse, and long-term use above 400°C is not recommended.

Conclusion: 

In the American standard system, when using carbon steel pipes, the following selection options can be considered:

a. Temperature > 425°C: Ordinary carbon steel cannot be used. Please use chromium-molybdenum alloy steel (such as ASTM A335 P11/P22).
b. Temperature between -29°C and 425°C: Use A106 Gr.B with confidence. This is the most economical and reliable choice.
c. Temperature < -29°C: Exercise caution. First, check the "exemption curve" according to ASME B31.3. If the thickness is thin and the stress is low, an exemption may be granted. Otherwise, switching to A333 Gr.6 low-temperature carbon steel is the easiest option.