Introduction to degreasing, pickling, passivation, and pre-filming of petrochemical static equipment

In the installation and construction of petrochemical equipment, specific cleanliness requirements are often mandated by system design, such as the need to avoid oils and contaminants. This necessitates special treatments of the equipment’s internal surfaces, including degreasing, pickling, passivation, and pre-filming.

Petrochemical Static Equipment

Degreasing of Equipment

In petrochemical engineering, it is crucial to degrease equipment, especially when the petroleum equipment, transport, and storage materials are prone to combustion or explosion upon contact with oils and other organic substances. Degreasing is also necessary when these organic substances can mix with the materials being transported or stored, altering their properties, or when the purity and quality of the product could be compromised. Additionally, degreasing is required before pickling processes according to design and specification requirements.

Degreasing of static equipment should be conducted after passing strength tests. The method used depends on the medium in contact, the structure, and the degree of oil contamination. Common methods include wiping, spraying, immersion, circulation, and tank dipping.

For machinery, any components that contact oil-sensitive mediums must be degreased before production. However, this should follow the completion of body installation, alignment, and adjustment of various gaps, after which the machine is disassembled for degreasing.

Pickling and Passivation

Requirements for Pickling

During construction, equipment with special internal cleanliness requirements should undergo pickling. The most common methods for pickling are tank immersion and system circulation. Typically, the pickling solution is composed of hydrochloric acid with a certain amount of surfactant added to enhance its effectiveness.

Passivation

Following pickling, equipment must be promptly passivated. Passivation involves using a solution that raises the pH value without causing iron hydroxide precipitation. This process neutralizes the acid residues that may have adhered to the inner walls during pickling, forming a passivation film on the surface. After passivation, the equipment should be rinsed with slightly alkaline water to protect the passivation film and prevent re-rusting when exposed to air. Sodium nitrite solution is commonly used for passivation. The processes of pickling, neutralization, and passivation are conducted in a continuous cycle.

Pre-Filming

Pre-filming, also known as chemical conversion coating, is a type of protective layer applied to metal surfaces. Especially after successful pickling and passivation, pre-filming can be employed to safeguard the equipment. With advancements in science and technology, the application of pre-filming in engineering to protect metal surfaces is becoming increasingly prevalent.

The treatments of degreasing, pickling, passivation, and pre-filming are essential for ensuring the cleanliness and longevity of petrochemical static equipment. These processes not only protect the equipment from contamination and corrosion but also enhance its overall performance and safety in petrochemical operations. By adhering to these procedures, petrochemical installations can achieve higher standards of cleanliness and durability, meeting the stringent requirements of modern industrial applications.