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Do you know what steps are involved in the leak‑testing procedure for stainless steel reaction vessels?
发布时间:2025-12-05
Stainless steel reactors are widely used in the chemical, pharmaceutical, and food industries. Their sealing performance is influenced by both the production process and the condition of the product. Leak testing is an essential step in verifying equipment integrity. The following outlines the procedures and key technical considerations for leak testing.
I. Pre-examination Preparation
The following tasks must be completed prior to the leak test:
Equipment Integrity Inspection
Confirm that all attachments welded to the vessel body—such as manholes, nozzles, and instrument connections—have been installed, and that the weld surfaces are free of oil, rust, or unremoved spatter. In accordance with the “Technical Supervision Regulations for Pressure Vessels,” welds subject to tightness testing shall not be painted.
Media Selection and Water Quality Control
Use fresh water with a temperature of no less than 5°C. For reactors constructed from 304/316L stainless steel, the chloride ion concentration in the water shall not exceed 25 mg/L. If an aluminum‑topped reactor is involved, use water that is non‑corrosive to aluminum.
Strengthen pre-inspection of the loop
Use compressed air at 0.1–0.2 MPa to perform leak testing on the welds of the reinforcing ring. If any leaks are detected, re-weld the affected area and repeat this procedure.
II. Hydrostatic Test
Foundation Settlement Monitoring
The water fill level has reached the designated operating liquid level. During the 48-hour pressure-holding period, record the initial settlement at hourly intervals. If the settlement exceeds the design value—typically 1/500 of the vessel diameter—the test must be halted and the foundation subjected to remedial treatment.
Vessel Strength Test
Maintain the set liquid level for 48 hours and inspect the vessel wall for any leakage or deformation. If leakage is detected, mark the location, drain the liquid to a point 300 mm below the leak, perform a repair weld, and then conduct a re‑pressurization water test.
Top-of-the-reactor test
(1) Pressure Test: Fill the vessel with water to the design liquid level, then increase the pressure to 1.1 times the design pressure (e.g., if the design pressure is 1.0 MPa, the test pressure is 1.1 MPa). Maintain this pressure for 30 minutes, and inspect the top of the vessel for deformation and check the welds for leaks (soap solution may be used to aid observation).
(2) Stability test: After filling the vessel to the set liquid level, drain the liquid to create a negative pressure (typically –0.05 MPa), and observe any changes in the shape of the vessel head. Following the test, open the vent valve to restore the vessel pressure to atmospheric pressure.
III. Operating Precautions
Temperature: During testing under conditions with significant temperature fluctuations, thermal expansion differences may lead to uneven contraction of the reactor vessel material. If operating in a low-temperature environment, preheat the reactor vessel to above 10°C.
Breather valve: Ensure the breather valve remains unobstructed during filling and draining. Large reactors may be equipped with a dual-breather-valve system.
Weld seam treatment: The repaired area shall be ground flush with the base metal and subjected to penetrant testing (PT) or magnetic particle testing (MT). Following treatment, a re‑water‑filling test shall be conducted.
IV. Post-Inspection Records and Follow-Up Arrangements
Data Recording: Establish a leak-test inspection file and record parameters such as pressure, temperature, and settlement.
Reinspection cycle:
(1) High-frequency-use equipment (operating more than 8 hours per day): Conduct a water-filling test every six months.
(2) Low-frequency equipment: Conduct a visual inspection and a pressure‑based leak test once per year.
Seals: For mechanical seals, the wear condition of the rotating and stationary rings should be inspected quarterly, with a replacement interval not exceeding two years; for gland packings, the compression force should be adjusted monthly, and the leakage rate should not exceed 5 drops per minute.
V. Industry Practice
A chemical enterprise once failed to detect a leak at the reactor vessel flange during the leak‑testing phase, resulting in a subsequent material spill. In its subsequent corrective measures, the company implemented a digital monitoring system that uses pressure sensors to track pressure fluctuations inside the reactor and leverages software for data analysis.
Leak‑testing of stainless steel reaction vessels can be carried out throughout the equipment’s service life, with specific technical guidelines for each stage—ranging from preliminary preparation and in‑process operation to post‑operation documentation.
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