Bolted flange joint assembly guidelines from ASME PCC1-2019

ASME PCC1-2019 : technical notes about sealing performance

Lotfi Grine, Eng. – Product Specialist at Robco

In the following technical notes, you will find valuable technical extracts from the ASME PCC1 2019 (bolted flange joint assembly (BFJA) guidelines) to help better understand sealing behaviour and produce a positive seal.

- Calculating Target Torque Values are based on the root area. The root areas are based on coarse-thread series for sizes 1 in. and smaller with 8-pitch thread series for sizes 1 1/8 in. and larger (Section H).

- The major long-term value of coated bolts is to protect against corrosion of the exposed threads and to minimize break-out and nut-removal torque, thereby promoting ease of joint disassembly (Section 7).

- Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code requires that nuts engage the threads for the full depth of the nut (Section 8.2).

- Start-up re-torque is performed when the temperature of the flange or bolts is between 150°C (300°F) and 230°C (450°F) or within 24 h of unit start-up if the joint temperature remains below 150°C (300°F). This temperature range and time window is selected to allow for the maximum amount of gasket relaxation prior to re-tightening while avoiding significant evaporation of lubricating oils from the anti-seize product. Loss of lubricating oils greatly reduces the accuracy of the torque. Start-up re-torque is typically not recommended for PTFE-based gaskets (Section 10.4).

- The life of the bolt can be extended by specifying a lower load (Section O-2).

- Leakage due to flange rotation may be due to concentration of the gasket stress on the gasket outer diameter causing damage or additional relaxation (Section O-2).

- The maximum permissible flange rotation (θgmax) at the assembly gasket stress and the gasket operating temperature must be obtained from industry test data or from the gasket manufacturer. There is presently no standard test for determining this value; however, typical limits vary from 0.3 deg for expanded PTFE gaskets to 1.0 deg for typical graphite-filled metallic gaskets (per flange) (Section O-4-1).

- The minimum permissible bolt stress (S_bmin) must be selected by the user. This value is intended to provide a lower limit such that bolting inaccuracies do not be come a significant portion of the specified assembly bolt stress, Sbsel. The value is typically in the range of 140 MPa to 245 MPa (20 ksi to 35 ksi) (Section O-4-1-c).

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