Which of the following indicates a change in essential variables for procedure qualification?

In the context of procedure qualification under API 1104, essential variables are parameters that, when changed, can significantly affect the properties of the weld. Each of the choices indicates an essential variable.

The pipe material group refers to the classification of materials based on their composition and properties. A change in the material group can influence factors such as the required preheat temperature, welding process adjustments, and filler material selection.

The position, fixed to roll, refers to the welding position in which the weld is performed, such as flat, horizontal, vertical, or overhead. Changing the welding position can impact the weld's mechanical properties and penetration, potentially requiring adjustments to the welding technique or parameters.

The direction of welding indicates whether the welding is being done in a left to right or right to left manner, among other techniques. This can influence the heat input and cooling rates during the welding process, also necessitating adjustments to maintain weld quality and integrity.

Since all these variables can significantly affect the welding procedure's outcome, recognizing that any change among them constitutes a change in essential variables for procedure qualification is crucial. Therefore, the choice indicating that all of the listed factors represent changes in essential variables is accurate and highlights the importance of maintaining strict control over these parameters during the qualification