Clearance Number

Incorrect. A clearance number refers to the number of consecutively inspected units found defect-free.

Incorrect. This is partially correct, but it doesn't specify the requirement for defect-free units.

Correct! This is the core definition of a clearance number.

Incorrect. This refers to the scope of inspection, not the clearance number concept.

Incorrect. Increased efficiency is a key benefit.

Incorrect. Reduced costs are a direct result of less intensive inspections.

Correct! Clearance numbers don't eliminate the need for regular inspections, but they adjust their frequency and intensity.

Incorrect. Clearance numbers enhance safety by ensuring thorough inspections until a certain level of confidence is reached.

Incorrect. Clearance numbers have a wider range of application.

Correct! This reflects the broad use of clearance numbers.

Incorrect. While drilling equipment maintenance might use them, it's not limited to this.

Incorrect. Production facilities are one area of application, but not the only one.

Incorrect. While cost is a factor, it's not the primary one.

Incorrect. Historical data is valuable, but the primary consideration is the risk associated with the task.

Correct! This is the most crucial factor influencing the clearance number.

Incorrect. Inspector availability is important for execution, but the clearance number is based on risk assessment.

Incorrect. Statistical soundness is essential.

Incorrect. Continuous monitoring is crucial for ensuring effectiveness.

Correct! The clearance number should be tailored to the specific risks of each task.

Incorrect. Record-keeping is essential for monitoring and decision-making.

Here's a possible solution for the exercise:

1. Initial Inspection Method:

A comprehensive initial inspection would involve:

• **Visual Inspection:** Thorough visual examination of the weld for surface defects, cracks, or inconsistencies.
• **Radiographic Testing (RT):** Using X-rays or gamma rays to detect internal defects such as porosity, slag inclusions, or lack of fusion.
• **Ultrasonic Testing (UT):** Using sound waves to identify internal flaws and measure weld thickness.
• **Magnetic Particle Testing (MT):** Detecting surface cracks or defects by applying magnetic fields and iron particles.

2. Determining the Clearance Number:

Given the high-risk nature of pipeline welds, a clearance number of 20 would be reasonable. This ensures a high level of confidence in the welding process before transitioning to a less stringent method.

Reasoning:

• **High Stakes:** Pipeline failure can have devastating consequences, including environmental damage, economic losses, and potential harm to human life.
• **Prioritization of Safety:** A higher clearance number reflects a greater emphasis on ensuring the integrity of the pipeline.
• **Statistical Significance:** A larger clearance number provides a more statistically robust sample to demonstrate consistency in the welding process.

3. Less Stringent Inspection Method:

After achieving the clearance number of 20, subsequent welds could be inspected using:

• **Visual Inspection:** A thorough visual inspection, coupled with a portable ultrasonic thickness gauge to confirm weld thickness.
• **Dye Penetrant Testing (PT):** A less intensive method for detecting surface defects by applying a dye solution.