Technical

U bend fin tube heat treatment

One: GB/T151-2014 regulations:

When there is a stress to resist or required to eliminate residual stress, the carbon steel and low alloy steel U -shaped heat exchanges can be held at least 150 mm. Other materials U -shaped heat exchanges hot tube hot treatment reasons for supply and demand for negotiation between supply and demand.

Two: NB/T47019.1-2021 regulations:

When the contract stipulates, after the U -shaped heat exchanges, the U -shaped bending part and the direct tube section of at least 150mm shall be conducted, and the thermal treatment specification shall be specified by the design document or ordering contract.

Three: Regulations from some technical information:

1.Carbon steel and low alloy steel cold -curved U bend fin tube:

a)The medium has a stress corrosion tendency to cope with the U bend fin tube bending section and the direct tube section including 150mm for eliminating stress thermal treatment.

b)Cold forming deformation rate (100r/R% -where R is the outer radius of the steel pipe, R is the curved radius of the center line of the steel pipe) is greater than 50%of the lower limit of the extension (AS) after the steel pipe standard is broken, and the remaining back extension is left behind after forming. Steel pipes with a length of less than 10%(AS) should be treated with annealing to restore mechanical properties.

c)There are impact test requirements, steel pipes with a deformation rate of greater than 5%should be treated with annealing to restore mechanical properties.

2.Austenite stainless steel cold -curvedU bend fin tube, generally does not perform heat treatment. If it is used for a stress corrosive medium or a bending radius <5D (outer diameter of the steel pipe)), solution should be performed.

3.Croneis/Austeen bilateral stainless steel cold bendingU bend fin tube shall be soluble. G is used for low -temperature heat exchangers. When the curved radius is <10D (steel pipe diameter) when the cold bending is bending, stress thermal treatment should be performed.

4.Nonferrous metal pipes generally do not eliminate stress heat treatment. When necessary, the stress thermal treatment can be eliminated according to the methods and requirements of both parties in supply and demand.

Four:HG/T20584-2020 regulations:

After the steel pipe is cold, if the deformation rate (the deformation rate can be calculated according to the following method) exceeds the following range, the heat treatment should be performed after forming:

1)The outer fiber deformation rate of carbon steel and low -alloy steel steel pipes should not be greater than 1/2 of the elongation of the stipulated elongation of the steel pipe standard or the remaining extension rate of the outer material should be less than 10%;

2)The outer fiber deformation rate after stainless steel steel tube bending tube should not be more than 1/2 of the elongation rate specified by the steel pipe standard, or the remaining elongation of the outer material should be less than 15%;

3)For steel pipes with impact toughness, the maximum deformation rate of its outer fiber should be less than 5%.

Calculation of steel pipe cold -curved fiber deformation rate can be calculated according to formula (F.1), formula (F.2), formula (F.3):

ε=max(ε1，ε2)............................(F.1)

ε1=100(S-S´)/S%............................(F.2)

ε2=100r/R%..................................(F.3)

Ε-Deformation(%)；

S-Steel pipeline nominal thickness,mm;

S´-The minimum thickness of the outer wall after the steel pipe is cold bending,mm;

R-Direct radius,mm;

R-Bend tube radius,mm.

Five:GB/T16507.5-2022 "Part 5: Manufacturing" stipulates:

Calculation formula for deformation rate after steel pipe bending:ε=100r/R%

For the determination of the deformation rate after the steel pipe is bending, please refer to GB/T16507.5-2022 "Part 5 of the Water Pipe Boiler: Manufacturing".