The technical requirements for stainless steel tubes in a shell and tube heat exchanger
What is the technical requirements for stainless steel tubes in a shell and tube heat exchanger?
- Material Specification and Standards
- Compliance: Tube material shall conform to the ASME Section II material specification
- Preferred Type: Seamless tubes are preferred, although welded tubes are acceptable. If welded tubes are offered, the type must be specified.
- Heat Treatment: Welded austenitic stainless steel tubes must be mill solution annealed.
- Testing and Inspection
- Non-Destructive Testing: All tubes must be tested by a non-destructive electric method, as described in Section V of the ASME Boiler and Pressure Vessel Code.
- Non-Destructive Testing: All tubes must be tested by a non-destructive electric method, as described in Section V of the ASME Boiler and Pressure Vessel Code.
- Corrosion Resistance
- Intergranular Corrosion Test: Where specified, austenitic stainless steel materials of pressure components (including tubes) shall be subjected to an inter-granular corrosion test as per ASTM A262.
- Test Method: The material shall initially be subjected to Practice A (Oxalic acid etch test combined with metallographic examination). If the structure is unacceptable, the material shall be further examined as per Practice E, or strictly as per any other practice specified in the drawing or specification.
- Painting and Coatings Restrictions
- Prohibited Paints: Aluminum, zinc, lead, or other low melting point metal-containing paints shall not be used for identification on stainless steels. Paints with chlorides shall also not be used on stainless steel.
- Prohibited Paints: Aluminum, zinc, lead, or other low melting point metal-containing paints shall not be used for identification on stainless steels. Paints with chlorides shall also not be used on stainless steel.
- Hydrostatic Testing Restrictions
- Chloride Content: Austenitic stainless steel exchangers or parts of exchangers shall be tested with water having a maximum total chloride content of 25 PPM.
- Post-Test Drying: To prevent stress corrosion cracking, the heat exchanger must be drained and thoroughly dried as soon as possible, but not more than 48 hours after testing. Drying should be done by blowing with dry air, and stagnant water should not be allowed to dry on the interior surfaces.
- Rinsing for Stress Corrosion Prevention: Where the possibility of austenitic stainless steel stress corrosion cracking exists (e.g., in bellows or when the service temperature is above 70°C), the exchanger shall be rinsed with demineralized water immediately after hydraulic testing and before drying.
