Complete Analysis of Economizer Tube Grades HT150 and HT200 (GB/T 9439 Gray Cast Iron)
HT150 and HT200 are grey cast iron grades specified in GB/T 9439, where the letters HT come from the initials of the Chinese name for grey cast iron and the number after them is the minimum tensile strength in MPa. When they are used for economizer tubes, the two grades differ clearly in strength, wear resistance and applicable duty. An economizer sits in the rear flue of the boiler, and its tubes face flue gas scour outside and feedwater pressure inside, so material selection has to balance strength against casting behaviour.
Meaning of the grade
HT150 means that a φ30 separately cast test bar has a tensile strength of not less than 150MPa, and HT200 means a test bar of the same size reaches not less than 200MPa. The grade number only gives the lower limit of tensile strength, it does not directly stand for heat resistance temperature, and it is not equal to the strength at the actual wall thickness.
Property comparison
HT150 has lower strength, but its casting fluidity is fairly good, it forms easily, damps vibration and conducts heat well, and it costs less. Its drawbacks are poor high-temperature resistance and insufficient toughness, so it easily cracks under thermal stress. HT200 has higher strength and hardness than HT150, balanced overall properties, and better wear resistance and thermal shock resistance than HT150. In boiler fittings HT200 offers fairly good value for money.
| Grade | Tensile strength | Properties and typical uses |
|---|---|---|
| HT150 | φ30 test bar ≥150MPa | Good casting fluidity, good damping and heat conduction, low cost; poor heat resistance, low toughness; used for passive grates of small domestic boilers, furnace door bases, light castings and non-pressure shells |
| HT200 | φ30 test bar ≥200MPa | Higher strength and hardness, better wear and thermal shock resistance; used for small and medium chain grate bars, ash doors, fire doors and regular boiler accessories |
Use in the boiler industry
For low-temperature, lightly loaded positions where cost control matters, HT150 can be chosen; for long-running mainstream standard fittings that take slight heat and wear, HT200 is chosen. Neither grade is recommended above 650℃, where RTSi5 or RQTSi5 heat-resistant cast iron should be used instead. In export quotations the two grades are written as Gray Cast Iron HT150 and Gray Cast Iron HT200.
Related News
