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Boiler Quality Plates

Large cylindrical pressure-holding components like drums, RH headers, blowdown tanks and so on are required to be made from BQ plates.

BQ plate is primarily a very high-quality, fully deoxidised, mild steel (MS) plate of medium to high thickness, suitably alloyed where necessary to withstand high p & t. The essential requirements are

  • Very good weldability
  • Assured and verified high-temperature properties
  • High tensile strength even at high temperatures

BQ plates are available in three classes of metallurgy

  1. CS (low, medium and high C)
  2. Low and medium AS
  3. High AS—not in ASME steels

CS Plates

Low CS has good weldability while high CS has good tensile strength.

The American practice prefers

  • CS for both LP and HP applications and
  • Thick CS to thinner AS drums

The European method is to avoid C > 0.25% and adopt AS plates for HP and have thinner drums.

High CS plates of SA 515, 516 and 299 are extensively used for generally thickness up to ~40, <100 and >100 mm for the three steels, respectively.

Low and Medium AS Plates

SA 302 is a very popular low-alloy American steel employed for high PS & TS. For SH and RH headers of large diameter, when they are required to be rolled out of plates, medium- and high-AS plates are regularly employed.

High AS Plates

High AS plates are not listed in ASME standards but are routinely used in Europe to reduce the drum and header thicknesses. A thin drum is helpful in cycling duty of boilers.

Alloy plates are preferred in European practice.

Boiler Quality Plates to ASME Specification are given below:


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