Strictly speaking, the present piping codes give no specific limits for local stresses. As an industry practice, the calculated local stress is added to the general pipe stress and then compared with the pipe stress allowables specified by the applicable code. As an example, the total (general plus local) pipe stresses for ASME Class 2 and 3 piping shall satisfy the following equations ⬇️
Local Stresses⏬
1. Design loading
2. Service loadings
3. Sustained and thermal expansion loading
4. Local stress limit loading
1. Design loading
2. Service loadings
3. Sustained and thermal expansion loading
4. Local stress limit loading
Local Stress Due to Restraint of Pipe Radial Expansion⬇️
The membrane and flexural stresses can be calculated as follows⏬
In the case of the local stress produced by restraint to the pipe radial expansion SL = SL1 = 0, For fillet weld, i = 2.1 should be used. In addition, the stress check on limit loading is required. Here, SL3 = SL2.
Local Stress Due to Contact⬇️
The membrane and flexural stresses can be calculated as follows:
The membrane and flexural stresses can be calculated as follows:
Other Types of Local Stresses ⏬
The two types of local stresses previously described are commonly encountered by stress analysts. Detailed descriptions and analysis methods for other types of local stresses such as the local stresses at integral welded attachments to pipe (e.g., lugs and trunnions) can be found in technical publications, Welding Research Council Bulletins 107 and 198, and ASME Code Cases.
The two types of local stresses previously described are commonly encountered by stress analysts. Detailed descriptions and analysis methods for other types of local stresses such as the local stresses at integral welded attachments to pipe (e.g., lugs and trunnions) can be found in technical publications, Welding Research Council Bulletins 107 and 198, and ASME Code Cases.
ANALYSIS OF INTEGRAL WELDED ATTACHMENTS (IWA)⬇️
Integral Welded Attachments are often used to support piping systems. The local stresses in the piping at IWA locations are commonly evaluated using the Welding Research Council (WRC) Bulletin #107 approach,21 which is based on Bijlaard’s work. Generally.
Integral Welded Attachments are often used to support piping systems. The local stresses in the piping at IWA locations are commonly evaluated using the Welding Research Council (WRC) Bulletin #107 approach,21 which is based on Bijlaard’s work. Generally.
The various methods for local stress evaluations can be categorized in accordance with the following list. (Friction-induced loads due to weight and thermal expansion, if applicable, should be included.)
1. Stress intensification factor (SIF) approach for certain configurations
2. WRC Bulletin #107 approach with limitation on ß (attachment parameter) and γ (shell parameter) parameters
3. ASME Code cases approach
4. Approach based on utilization of any available finite element analysis (FEA) results or published data
5. Rigorous FEA approach
1. Stress intensification factor (SIF) approach for certain configurations
2. WRC Bulletin #107 approach with limitation on ß (attachment parameter) and γ (shell parameter) parameters
3. ASME Code cases approach
4. Approach based on utilization of any available finite element analysis (FEA) results or published data
5. Rigorous FEA approach
SIF Approach ⏬
In this method, the local stresses are not evaluated directly but are indirectly accounted for by applying a SIF to the general piping stresses.
The SIF approach has the following limitations:
• Applicable to some specific IWA configurations only
• Not applicable to lugs, irregular shapes, and so forth
In this method, the local stresses are not evaluated directly but are indirectly accounted for by applying a SIF to the general piping stresses.
The SIF approach has the following limitations:
• Applicable to some specific IWA configurations only
• Not applicable to lugs, irregular shapes, and so forth
The SIF approach has the following limitations: ⬇️
1- 360° (full) wrapper plates. This configuration is no longer a local stress problem.
A SIF (i) of 2.1 or 1.3 can be applied, depending on the applicable code.
2- 180° wrapper plates. The following SIFs are recommended by Rodabaugh (see Fig. B4.5e):
i = 4.2 for the run pipe torsional moment (Mtr) component
i = 2.1 for the run pipe out-of-plane bending moment (Mobr) component
i = 1.3 for the run pipe in-plane bending moment (Mibr) component
3- Circular trunnion/stanchions on straight pipe. Consider the configuration as a reinforced tee (RTEE) and intensify the general piping stresses using a SIF (i) of RTEE per the applicable code requirements. Since there is no hole made in the pipe’s pressure boundary, the run pipe thickness can be considered as a
reinforcement. If there is a pad, the pad thickness can be considered as an additional reinforcement. Of course, the codes limit the effective thickness of reinforcement [(te)max = 1.5 × t].
4- Attachments on fittings. Cross multiplication of SIFs (for example, a round
attachment on elbow or on a tee) can be used (elbow SIF × RTEE SIF or TEE SIF
× RTEE SIF).
1- 360° (full) wrapper plates. This configuration is no longer a local stress problem.
A SIF (i) of 2.1 or 1.3 can be applied, depending on the applicable code.
2- 180° wrapper plates. The following SIFs are recommended by Rodabaugh (see Fig. B4.5e):
i = 4.2 for the run pipe torsional moment (Mtr) component
i = 2.1 for the run pipe out-of-plane bending moment (Mobr) component
i = 1.3 for the run pipe in-plane bending moment (Mibr) component
3- Circular trunnion/stanchions on straight pipe. Consider the configuration as a reinforced tee (RTEE) and intensify the general piping stresses using a SIF (i) of RTEE per the applicable code requirements. Since there is no hole made in the pipe’s pressure boundary, the run pipe thickness can be considered as a
reinforcement. If there is a pad, the pad thickness can be considered as an additional reinforcement. Of course, the codes limit the effective thickness of reinforcement [(te)max = 1.5 × t].
4- Attachments on fittings. Cross multiplication of SIFs (for example, a round
attachment on elbow or on a tee) can be used (elbow SIF × RTEE SIF or TEE SIF
× RTEE SIF).