Materials used for manufacturing the compressor unit shall be brand new, accompanied by mill test certificates, material composition analysis reports, heat treatment reports and other test documents. The manufacturer shall conduct re-inspection of incoming materials when necessary. Obsolete, inferior or scrap materials are not permitted.

Pressure-bearing castings shall not be subjected to repair welding without the buyer’s special approval. Post-weld heat treatment is required for major repair welds.

The casing shall be made of steel under the following conditions: (1) Air or non-flammable gas with a design pressure exceeding 1.765 MPaG; (2) Air or non-flammable gas where the calculated discharge temperature exceeds 235°C at any operating point within the operating range at maximum continuous speed; (3) Flammable or explosive gas with a design pressure exceeding 0.54 MPaG, or where the calculated discharge temperature exceeds 180°C at any operating point within the operating range at maximum continuous speed.

When the operating temperature is lower than -30°C, pressure-bearing components shall adopt alloy steel or special carbon steel suitable for low-temperature service. The material impact strength at the minimum operating temperature shall not be less than 20.6 N·m