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Tubesheet Welding
MLP for different ASME joints .
Key examples First example : Fillet weld – full strength weld joint
a r
= ( 0.75d o ) 2 + 2.73t ( d o - t ) f w f d
– 0.75d o
Sa = 92.4 Mpa ….. Tube all . stress ASEM sec . II part D St = 138 Mpa ….. Tubesheet all . stress ASEM sec . II part D Fw = Sa / Sw = 1 ( Sw is smaller of Sa and St ) Fd = 1 for full strength weld
a r
= [( 0.75 × 19.05 ) 2 + 2.73 × 2.018 × ( 19.05 - 2.018 ) × 1 × 1 ] - 0.75 × 19.05
ar = 2.93 mm ……. 1,4t = 1.4 × 2.018 = 2.825 mm af >= greater of ar or 1.4t …….. af = 2.93 mm MLP Throught distance = af / 2 = 2.93 / 2 = 2.07 mm
Calculated MLP = 2.07 mm MLP as 2 / 3 t = 1.405 mm …… per API 660
Second example : Groove weld – full strength weld joint
a r
= ( 0.75d o ) 2 + 1.76t ( d o - t ) f w f d
– 0.75d o
Sa = 92.4 Mpa ….. Tube all . stress ASEM sec . II part D St = 138 Mpa ….. Tubesheet all . stress ASEM sec . II part D Fw = Sa / Sw = 1 ( Sw is smaller of Sa and St ) Fd = 1 for full strength weld
a r
= [( 0.75 × 19.05 ) 2 + 2.73 × 2.018 × ( 19.05 - 2.018 )
× 1 × 1 ] - 0.75 × 19.05 ar = 2.93 mm ……. ag >= greater of ar or t …….. ag = 2.93 mm MLP = depth of groove = ag = 2.93
Calculated MLP = 2.93 mm MLP as 2 / 3 t = 1.405 mm …… per API 660
Example 1 .
Example 2 .
Please note the big difference between the calculated value considering the design calculations and the general rule form API 660 .
In these examples , the following material and design data is assumed and will be used for both examples :
• Tube material : carbon steel ASME SA 179
• Tubesheet material : carbon steel SA 266 Gr . 2
• Tube DO : 19.05 mm , tube thickness BWG 14 ( 2.108 mm )
• Design temperature ( to be used for getting the material allowable stresses ): 200 ° C
Conclusion A mock-up of tube-to-tubesheet assembly is a vital requirement to achieve good quality , long life joints . The successful mock-up will represent the actual conditions of the production joints and provide required inputs to control all essential and important parameters controlling the quality of the joints depend on many aspects covering the dimensions control , tools to be used , procedure and sequence to be applied , quality checks and testing . The mock-up should be a reference point in the ITP ( Inspection and Test Plan ) of the exchanger . Users and owners should incorporate the application of a mock-up to ensure that detailed procedure is welldeveloped and reviewed including all the aforementioned aspects in addition to draft for the final report form .
About the author
Baher Elsheikh is a Mechanical Engineer at SABIC . He has twenty years of experience in the engineering , reliability , construction , commissioning and inspection management of pressure equipment , piping systems , fired heaters , and power boilers .
34 Heat Exchanger World April 2023 www . heat-exchanger-world . com