QW-320 & 321 provides this information, which is summarised below:
Immediate Retest Using Visual Examination
A welder who fails to satisfy the visual examination criteria for a welded test coupon is allowed an immediate retest but must make two consecutive test coupons, for each test position failed, and both must satisfy the visual examination criteria.
The examiner may select one of the two test coupons that satisfied the visual examination for conducting the mechanical testing.
Immediate Retest Using Mechanical Testing
A welder who fails to satisfy the mechanical test criteria for a test coupon is allowed an immediate retest but must make two consecutive test coupons, for each test position failed, and both must satisfy the mechanical test criteria.
Immediate Retest Using Radiography
A welder who fails to satisfy the radiographic acceptance criteria for a welded test coupon is allowed an immediate retest but must make two consecutive test coupons, for each failed test, and both must satisfy the radiographic acceptance criteria.
A welder who fails the production weld alternative test (radiographic requirements) may be retested by radiography of twice the required length of production weld (or number of pipe circumferences) of the same, or consecutively made, production welds. To qualify, he must satisfy the radiographic requirements for this welding. He is allowed to repair his defective welds or this may be done by another qualified welder.
Further Training
A welder who fails a retest is expected to undergo further training or practice before attempting a new test but the Code does not give any details of type or duration of training.
A new test is required for each welding position that he failed to meet the acceptance requirements.