Question 34 1AE01 - First Assistant Engineer

The Correct Answer is A. **Why option A ("descaled by using a pickling solution") is correct:** New piping fabricated for hydraulic systems invariably contains contaminants that must be removed before installation. The most critical contaminant is mill scale (iron oxide) formed during the high-temperature manufacturing processes (welding, bending, drawing). Mill scale is abrasive, chemically reactive, and easily dislodged by hydraulic fluid flow, leading to rapid component damage (especially pumps and valves) and system failure. Descaling involves chemically removing this scale, often through a process called **pickling**, where the piping is immersed in an acidic solution (like sulfuric or hydrochloric acid) specifically designed to dissolve the mill scale and rust. This process is essential and precedes final flushing/cleaning operations, making it the primary and necessary initial step for preparing new hydraulic piping. **Why the other options are incorrect (or incomplete/secondary):** * **B) hydrostatically tested to 100% of maximum working pressure:** Pressure testing (hydrostatic or pneumatic) is an important quality control step performed to verify the structural integrity and leak-tightness of the fabricated piping assembly. However, testing is *secondary* to cleaning. If testing is performed *before* descaling, the internal scale remains and poses a major contamination risk immediately upon system startup. Therefore, descaling/cleaning must occur first. * **C) cleaned using a water-based detergent:** While the piping must be thoroughly cleaned and flushed *after* descaling (to remove residual pickling acid and any manufacturing debris), using a simple water-based detergent alone is insufficient to remove hardened mill scale and rust. Detergents are used for final cleaning and passivation, not for the primary task of descaling the metal surface. * **D) all of the above:** Although all these steps (descaling, testing, and final cleaning) are crucial parts of the overall preparation process, the question asks what the piping *should* be prior to installation. **Descaling (A)** is the necessary foundational step for ensuring the cleanliness required for hydraulic operation. If forced to choose the single most necessary step related to internal cleanliness upon fabrication, descaling is the answer, making A the most fundamentally correct choice over D, which implies an order of operation that is often incorrect (cleaning precedes testing) and includes steps (B and C) that are insufficient without A.