Field welding on containers shall be limited to attachments on ____________ installed by the manufacturer.

The correct answer is that field welding on containers shall be limited to attachments on non-pressure parts installed by the manufacturer. This is based on safety standards and regulations concerning the integrity of pressure vessels. Non-pressure parts are components of the container that do not experience internal pressure and therefore do not compromise the structural integrity or safety of the container when welded.

Field welding on pressure parts could risk creating weak points or altering the designed pressure tolerance of the container, potentially leading to dangerous situations. Thus, regulations are strict about welding only on non-critical components that manufacturers have deemed safe for modification. This approach minimizes the risk of failure in high-pressure situations, ensuring the safety of the equipment and its operation.