Performance Differences of High-pressure Boiler Tubes in Different Materials

High-pressure boiler tubes are the core components of the boiler system. They are mainly used to transport high-temperature and high-pressure media (such as superheated steam, high-temperature flue gas, etc.). Their performance directly affects the safety and efficiency of the boiler. Different boiler pipe materials have significant differences in high temperature resistance, oxidation resistance, strength, corrosion resistance, and processing technology.

The following is a performance comparison analysis of common materials:

Carbon steel (such as 20G)

Composition characteristics: Carbon content is about 0.2%, the main alloying elements are iron and carbon, and a small amount of silicon and manganese.

Advantages:

Low price, good processing technology (excellent welding and cold bending performance).

The mechanical properties at room temperature are stable and suitable for medium and low temperature and medium and high pressure scenes.

Disadvantages:

Poor high temperature resistance, long-term use temperature generally does not exceed 450, and the strength decreases significantly at high temperature.

Weak oxidation resistance, easy to oxidize and peel in high-temperature flue gas or steam.

Application scenarios:

Water-cooled wall tubes and economizer tubes of medium and low pressure boilers, etc.

Steam pipes with low requirements for high temperature resistance.

Low alloy heat-resistant steel

1. 15CrMoG (P12, T12)

Composition characteristics: Contains about 1.0% Cr and about 0.5% Mo, belonging to Cr-Mo low alloy steel.

Advantages:

High temperature resistance is improved, long-term use temperature can reach 540, and good thermal strength (creep resistance) is maintained at high temperature.

Oxidation resistance is enhanced, Cr element forms an oxide film (Cr₂O₃), delaying high temperature oxidation.

Good weldability, preheating before welding and heat treatment after welding are required.

Disadvantages:

Low alloy element content, pearlite spheroidization may occur under high temperature and high pressure for a long time, affecting life.

Application scenarios:

Superheater tubes, reheater tubes, and main steam pipes of high-pressure boilers (wall temperature ≤540).

2. 12Cr1MoVG

Composition characteristics: Contains about 1.2% Cr, about 0.3% Mo, about 0.2% V, and vanadium (V) is added to strengthen the grains.

Advantages:

The thermal strength is better than 15CrMoG, the long-term use temperature can reach 580, and the creep resistance is better.

Good structural stability, V element inhibits carbide aggregation and delays pearlite spheroidization.

Disadvantages:

The welding process requires higher requirements (preheating temperature and post-weld treatment must be strictly controlled).

Application scenarios:

Ultra-high pressure, subcritical boiler high temperature section superheater and reheater tubes (wall temperature ≤ 580).

High alloy heat-resistant steel (martensitic stainless steel)

1. T91/P91 (9Cr1MoVNb)

Composition characteristics: Contains about 9% Cr, about 1% Mo, and adds strong carbide forming elements such as V and Nb.

Advantages:

High temperature resistance is significantly improved, and the long-term use temperature can reach 600~650, which is suitable for supercritical boilers.

Strong oxidation resistance, high Cr content, forming a dense oxide film, excellent resistance to steam oxidation and flue gas corrosion.

High strength, the martensitic structure has good comprehensive mechanical properties after tempering.

Disadvantages:

Welding is difficult, and the welding process needs to be strictly controlled (such as preheating temperature ≥200, post-weld heat treatment).

High cost and high alloy element content.

Application scenarios:

High temperature superheater and reheater tubes of supercritical and ultra-supercritical boilers (wall temperature ≤620).

High temperature and high pressure steam pipelines.

2. T92/P92 (9Cr2WMoVNbB)

Composition characteristics: Add W (about 2%) and B (boron) on the basis of T91, and reduce Mo content.

Advantages:

Higher thermal strength, W and B strengthen grain boundaries, creep rupture strength is better than T91, and the operating temperature can reach 620~650.

Excellent oxidation resistance and corrosion resistance, suitable for more severe high temperature and high corrosion environment (such as sulfur-containing flue gas).

Disadvantages:

The welding process is complex, and the welder's skills and equipment are required to be high.

Application scenarios:

High temperature section heating surface tubes of ultra-supercritical boilers (such as final superheaters and reheaters).

Austenitic stainless steel (such as TP304H, TP347H)

Composition characteristics: Contains about 18% Cr, about 8% Ni (304H) or adds Nb (347H), and the austenite structure is non-magnetic.

Advantages:

Excellent high temperature resistance, long-term use temperature can reach 700~800, and the maximum short-term temperature can reach 1100.

It has strong oxidation resistance and corrosion resistance. Cr and Ni form a stable oxide film, which is suitable for highly corrosive media (such as flue gas containing chlorine and sulfur).

Good plasticity and toughness, excellent processing formability (such as bending and flaring).

Disadvantages:

Poor thermal conductivity, pay attention to heat dissipation when using to avoid local overheating.

The cost is extremely high, and thermal cracks are prone to occur during welding. Matching stainless steel welding rods are required.

Application scenarios:

The highest temperature section heating surface of ultra-supercritical boilers (such as superheater outlet section, reheater high temperature section).

High temperature and high pressure corrosion-resistant pipelines in chemical, nuclear power and other fields.

Article source: https://article-realm.com/article/Business/74965-Performance-Differences-of-High-pressure-Boiler-Tubes-in-Different-Materials.html