1. The allowable deviation of the outer diameter and wall thickness of the hot-rolled, hot-extruded, and hot-expanded low and medium pressure boiler steel pipes:
1) If the outer diameter is less than 159mm, the outer diameter deviation of ordinary grade +-1.0% (minimum +-0.50mm%) advanced +-0.75% (minimum +-0.40mm%)
2) Ordinary grade with outer diameter greater than 159mm +-1.0%, advanced +-0.9%.
3) If the wall thickness deviation is less than 20mm, ordinary grade +15%-12.5% (minimum 0.45mm-0.35mm), advanced +-10% (minimum +-0.30mm).
4) The allowable deviation of the wall thickness of the thermally expanded steel pipe with an outer diameter greater than 351mm is +-15%.
2. Allowable deviation of outer diameter and wall thickness of cold drawn or cold rolled low and medium pressure boiler tubes:
1) Ordinary grade +-0.4mm with outer diameter of 10-30, advanced +-0.2mm.
2) Ordinary grade +-0.45mm with outer diameter greater than 30-50, advanced +-0.25mm.
3) Ordinary grades with an outer diameter greater than 50 +-1.0%, advanced grades +-0.75%.
4) Wall thickness deviation of 1.5-3.0 allows +15%-10%, and advanced +-10%.
5) Normal grade with thickness greater than 3.0 +12.5%-10%, advanced +-10%
Length, bending and delivery quality of low and medium pressure boiler tubes:
Size specifications, outer diameter, wall thickness and theoretical quality of boiler steel pipes shall comply with the regulations.
Length: 1. The usual length, hot-rolled, extruded, hot-expanded steel pipe length is 4-12m. Cold-rolled and cold-drawn steel pipes have a length of 4-10.5m.
2. The length of the fixed length and the length of the double length should be within the normal length range, and the allowable deviation of the total length is +20mm. The specified incision margin should be reserved for each length of the ruler; the outer diameter is less than 159mm, 5-10m, and the outer diameter is greater than 159mm, 10-15mm.
Bending: 1.5mm/m if the wall thickness is less than 15mm, 2.0mm/m if the wall thickness is greater than 15mm, and 3.0mm/m if the outer diameter is greater than 351mm.
Both ends of the boiler tube should be perpendicular to the axis of the steel tube, and the burrs should be removed.
The out-of-roundness and wall thickness of boiler tubes shall be negotiated by both parties according to the requirements of the buyer, and shall be indicated in the contract.The out-of-roundness and wall thickness of the same section of steel pipe shall not exceed 80% of the outer diameter and wall thickness tolerances, respectively.