The proper procedure for pressurizing a double walled tank includes:

The proper procedure for pressurizing a double walled tank includes:

• A. Pressurizing the interstice before pressurizing the primary tank to conduct a soap water test first.
• B. Pressurizing the primary tank and the interstice immediately afterwards
• C. Pressurizing the primary tank and the interstice following the recommended test duration
• D. Pressurizing the primary tank and interstice simultaneously to avoid causing damage to either tank wall.

Answer: (C)

The test sequence is designed to verify each barrier of a double-walled tank without interference between tests. The correct approach is to complete the inner tank pressure test and hold it for the recommended duration, then proceed to pressurize the interstitial space. Doing the inner tank test first ensures any loss of pressure can be attributed to the inner wall and is detected during the specified hold time. Only after that duration is the interstice pressurized to check for leaks between the walls. This ordering avoids masking inner-wall leaks, prevents unnecessary stress or confusion from simultaneous or premature interstice testing, and aligns with standard procedures for reliable, valid results.

The test sequence is designed to verify each barrier of a double-walled tank without interference between tests. The correct approach is to complete the inner tank pressure test and hold it for the recommended duration, then proceed to pressurize the interstitial space. Doing the inner tank test first ensures any loss of pressure can be attributed to the inner wall and is detected during the specified hold time. Only after that duration is the interstice pressurized to check for leaks between the walls. This ordering avoids masking inner-wall leaks, prevents unnecessary stress or confusion from simultaneous or premature interstice testing, and aligns with standard procedures for reliable, valid results.