How much undercut is allowed on the root pass of the B pressure weld test?

How much undercut is allowed on the root pass of the B pressure weld test?

• A. 0
• B. 1/16 inch
• C. 1/8 inch
• D. 1/4 inch

Answer: (A)

Undercut is a groove melted into the base metal along the weld toe that reduces the weld throat at the root. For the root pass of a B pressure weld test, there must be no undercut, because any loss of base metal at the root weakens the joint and can compromise its ability to hold pressure. Therefore, zero undercut is required. The other options would indicate some depth of groove at the root, which would fail the acceptance criteria. To prevent undercut, control travel speed and heat input so the root is properly fused without gouging into the base metal, and ensure the weld fills the root uniformly before adding subsequent passes.

Undercut is a groove melted into the base metal along the weld toe that reduces the weld throat at the root. For the root pass of a B pressure weld test, there must be no undercut, because any loss of base metal at the root weakens the joint and can compromise its ability to hold pressure. Therefore, zero undercut is required. The other options would indicate some depth of groove at the root, which would fail the acceptance criteria. To prevent undercut, control travel speed and heat input so the root is properly fused without gouging into the base metal, and ensure the weld fills the root uniformly before adding subsequent passes.