Gate Valves Leakage 2

[juancito]

Dear all,
During the pressure test of a piping system, 3 out of 20 3/4" #800 gate valves had a minor leakage,(according to customer inspector about 1 drop per minute). These valves were SW/NPT and the leak was detected once removed the sealing plug inserted in the threaded side of the valve.
So,is some minor leakage accepted by API-598? (if this is the applicable norm).
Thanks in advance

 

[PVRV]

1. Reference to API-602, cl. 5.2 (PR as per API 598)

2. Note: API-598 requires the tests to be preformed at the
manufacturer Plant, cl. 3.1

3. Type of tests required (Table 1-A:

3.1 Shell
3.2 Back seat
3.3 Low Pressure Closure

4. For shell & backseat tests to visible leakage is
permitted.(cl.3.9.1)

5. *Closure Tests (Table 5)

5.1 The maximum allowable leakage rate (NPS <=2)

5.1.1 ZERO for all resilient seated valves
5.1.2 ZERO drops (no visible leakage) metal
seated valves
5.1.3 Less than one bubble for gas testing of
metal seated valves.

6. API 6D (1999)

6.1 Cl. 10.4.4, No visible Leak for soft seat valves
6.2 Refer to ISO 5208, Rate D for metal seated valves.



References;
API 598 7th Edition
API 602 7th Edition

 

[juancito]

THANKs A LOT PVRV! for the usefull and precise information you provided.

 

[stewbaby]

For what it is worth, from the practical side:

Welding procedure / practices on the SW connection can greatly help prevent this type leakage. We had this problem until we started removing the bonnets / stem / seat from the valve body until body is welded into place. Also, once valve body is tacked in place it is evenly pre-heated by torch before the SW is completed.

 

[PVRV]

juancito,

Please advise if you require information on preventive measures against leakage.

 

[juancito]

Please PVRV, let me know your recommendations regarding preventive measures.
Thanks in advance

 

[PVRV]

A 1.5mm (1/16&quot internal gap between the male and female should be in place before welding. Random RT can be utilized for verification.

For details,
Refer to ANSI B31.3-2002,
Fig. 328.5.2C

Cheers