Page 2: Para 2 is added Page 2: Para 3 is amended Page 2 Para4 is amended and cautions has been been added added Page 2 Para5 , sketch has been added. Page 3 Para 11 is removed.
1 – Torque Level has been added for Flat face flanges as well with TF gasket o r Krol / Ziller Gasket.
This method statement covers the instructions for flange tightening at site for all diameters and both grooved face flanges (with O ring gasket) and flat face flanges (with EPDM / Compressed Asbestos Gasket). Moreover, this document outlines also the maximum recommended torque value that can be applied on the GRP flanges. 2 – Instructions:
1. Thoroughly clean the flange and the ‘O’ ring groove or EPDM/ CA gasket. 2. Check if the gasket has been stored in a manner that prevents creases or warp 3. Check that during both storage and handling, the sealing surfaces of the gasket are not damaged and are free of debris or surface contamination. 4. Position the gasket in the groove or on the face of the flange for EPDM/CA gasket and secure in position, if necessary, with small strips of adhesive masking tape. Caution1: DO Not tape the gasket in place in such a way that the tape runs across the sealing surface. This leaves potential leak paths across the gasket face. Caution2: DO NOT glue or stick the gasket in place with a material that will contaminate the sealing surfaces once the gasket is put into operation. Caution3: DO NOT assume that gasket, put in place before the flange is positioned, will automatically stay in position.
5. Make sure that the two flanges or connecting flange with valve or expansion joint is well aligned with GRP flanges. Make sure that the two mating flanges touch each other from inside or a gap of maximum 2-3mm should be allowed. Any misalignment or more gaps would require high bolt torque and could lead to high stress at flange and could cause damage.
Ref: AQAP-MS-002
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6. Insert bolts, washers, and nuts. All hardware must be clean and lubricated to avoid incorrect tightening. Washers must be used on all GRP flanges. 7. Using a torque wrench, tighten all bolts to 35 N-m (20 N-m for small dia pipes <= 250) torque, following standard flange bolt tightening sequences shown in figure 2.0. 8. The below table is showing the minimum and maximum torque level. Minimum level is required to achieve the sealing, maximum level is the maximum allowable for flange.
GRP Flanges Groove Face with O Ring Gasket Min Torque Level (N.m) Max Allowable Torque Level
20 20 34 34 34 68 68
30 40 70 80 110 125 125
GRP Flanges Flat Face with TF Gasket or EPDM (Krol & Ziller) Gasket DN Min Torque Level (N.m) Max Allowable Torque Level
25 – 80 100 150 – 200
20 20 30
30 35 50
250
30
55
Ref: AQAP-MS-002
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300 350-500 600-800
35 60 100
70 100 170
900-1100 1200-1400
160 200
220 300
9. Repeat this procedure, raising the bolt torque until the flanges almost touch at their inside edges or maximum bolt torque. Do not exceed this torque without consulting AQAP for advice.
10. Uniform pressure should be established over the flange face by tightening bolts in 7 N.m increments according to the sequence shown in figure 2.0. For flanges with more than 20 bolts, similar altering bolt tightening sequences shall be used. (As per ASTM D 4024-00)
11. Check bolt torque one hour later and adjust as seen necessary to the maximum torque. Figure 1: Flange Joints Grooved Face
