I am procuring Pipe bend with following specification for economizer section of Boiler:
Outer Diameter: 33.40mm
Length of pipe bend: 226mm
Material: A106 Grade B
Design Pressure: 800 PSIG
Design Temperature: 232 Centigrade = 450 Fahrenheit
Bend radius at Center-line of Bend = 40mm
Supplier is providing thickness of 2.5mm at extrados. I want to confirm that this thickness of 2.5mm at extrados is acceptable or not as per applicable ASME standard
I have calculated the thickness of bend, ,using ASME B31.1.
Using formula mention in 104.1.2 of ASME B31.1 for straight pipe minimum wall thickness through eqn(3)= 2.26mm
Using formula for extrados mention in 102.4.5 Bending of ASME B31.1 equation 3(B) , minimum required thickness, of a bend,after bending= 2.15mm
As obvious, thickness will decrease at extrados form 2.26mm to 2.15mm. Also for thickness calculation, I considered corrosion allowance of 1.5mm as material of bend is carbon steel and intended to be used in economizer section of boiler .
Note supplier is providing bend with thickness at extrados = 2.5mm
According to ASME B31.1 The minimum wall thickness at any point on the bend shall conform to (A) or (B) below.
(A) The minimum wall thickness at any point in a completed bend shall not be less than required by eq.(3) or (3A) of para. 104.1.2(A). According to this requirement 2.5mm is greater than 2.26mm. Therefore bend with 2.5mm extrados thickness is acceptable.
(B) The minimum required thickness, tm of a bend, after bending, in its finished form, shall be determined in accordance with eq. (3B) or (3C). I have used eqn 3B and thickness calculated is 2.15mm . Since 2.5mm is greater than minimum required 2.15mm thickness at extrados. Therefore 2.5mm thickness provided by supplier is acceptable.
Supplier is making bend from 3.38mm pipe and required thickness at edge of bend is 3.38mm which is fulfilled by supplier and after
bending, thickness and extrados becomes 2.5mm , I believe it is acceptable as it is fulfilling the two above mentioned conditions of standard.My question is that , does this is right approach for selecting 2.5mm extrados thickness bends using standard or I am making mistake if any??