Paper pulp and paper making Industry

The working environment for paper pulp production and paper making industry is highly corrosive, and can cause severe corrosive damage to technique equipments. Statistics show, the loss caused by corrosion is up to 6 dollars for each ton of paper pulp. In order to maintain smooth operation and to reduce cost, stainless steel and anti-corrosion alloy are widely used in paper pulp production, and have become the irreplaceable structure material in this area. When using different paper pulp and different pulp making technique, the brand of the stainless steel in use will differ accordingly, presently, the TP304, TP316, TP317, 254SMO, 654SMO and double phase stainless steel and so on, have been widely used in the production of different paper pulp.

1. Stainless steel used in paper pulp production.
(1) Mechanical pulp making
In the process of mechanical pulp making, as chemistry drugs are not used, the corrosive extent is not so severe as the pulp making with sulfate and sulfite. In the early time, stainless steel was not much used under such environment; in recent years, for the purpose to reduce the repairing fee of the normal material and to promote economic benefit, as well as to prevent the pollution to paper pulp caused by iron rust, stainless steel is now widely used in mechanical pulp making, shown in the following table:

The application of stainless steel in mechanical pulp making

(2) Pulp making with sulfate method
In the pulp making technique process with sulfate method, the corrosion of the medium is not as high as with the sulfite method. In this process, the wood in the floating sea, the salt water and chemical drugs in use will all make the technique medium contain certain chloride, thus increasing the equipment corrosion. Practice experiences show, TP304LN and TP316L can achieve a satisfying usage effect, and the application of stainless steel under this technique condition is shown in the table below:

The application of stainless steel in the pulp making with sulfate method

(3) Paper pulp making with sulfite method
The technique process of paper pulp making with sulfite method is one with the highest corrosion; in early time, the Calcium Hydrogen Sulfite that contains superfluous sulfur dioxide as the boiling liquid is used, this liquid is acidic, and can be only used to boil specific wood material. If the liquid is added with magnesium, sodium and ammonia to be treated as basic cooking liquor, then cooking liquor with different PH value can be acquired, and it can be applied to all kinds of wood material. As the chemical drug is expensive, and for the purpose of pollution prevention, the calcium hydrogen sulfite is forbidden to be released, thus it must be reclaimed through technique method like evaporation, etc, causing the processing equipment to be operated under severe corrosive environment. Equipments under this kind of environment shall bear sorts of corrosions including uniform corrosion, corrosive pitting, crevice corrosion, stress corrosion, abrasion, etc, so the material in use should have a higher grade than those used in the techniques illustrated above, the super austenite stainless steel （2RK65, 254SMO, 654SMO） and super double phase stainless steel have all been applied successfully. The application situations of stainless steel in the pulp producing process with sulfite method are shown in the table below:

Application of stainless steel in the pulp producing process with sulfite method

(4) Pulp producing with semichemical method
The technique process of the pulp producing with semichemical method is between the chemistry method and mechanical method, material choosing of which will differ according to different chemical method being chosen. The most common method is the neutral sulfite semichemical method, namely, NSSC method. The application of stainless steel in the technique equipments of pulp producing with semichemical method is shown in the following table:

Material in the technique equipments of Pulp producing with semichemical method

(5) Pulp producing with half wasted paper
The technique medium of pulp producing with waste water is not with very severe corrosion; in order to maintain the whiteness of the paper, TP304LN is commonly used as the equipment structure material; in the working procedure that requires the adding of chemical drugs (zinc hydrosulfite and sodium peroxide, sodium hypochlorite), TP316L steel has the satisfactory usage effect.

(6) Paper pulp bleaching
Paper pulp bleaching is the last working procedure, which requires chemical drugs. Different paper pulp making processes will require different bleacher with large discrimination. In the pulp producing with sulfate method or sulfite method, the bleaching should be operated when chlorine, alkali, hypochlorite and chlorine dioxide are used, and for the mechanical pulp making and semichemical pulp making, peroxide and hydrosulfite are often used in the bleaching. During the bleaching process, water circulation will be used, which will cause the chloride in technique medium to increase intensely, and adding chemical drugs in the technique process, the technique medium will become severely corrosive. For the purpose to operate smoothly, the anti-corrosion material chosen for the bleaching technique equipments should be regarded the lowest grade as TP316L，TP317。00Cr20Ni25Mo4.5Cu，00Cr18Ni20Mo6CuN; high grade material like the super double phase stainless steel and nickel-base anti-corrosion alloy etc. have been widely used; the technician shall choose properly according to the medium’s actual condition. The applications of stainless steel in the bleaching technique process are shown in the table below:

The application of stainless steel in the bleaching technique process

The application of stainless steel in paper pulp bleaching process in Japan

2   Paper making.
The production environment of paper making is not so highly corrosive like the technique medium of paper pulp making, but for the purpose of producing clean paper and easy maintenance, stainless steel is widely used in paper making technique process. The actual application situations are shown in the table below:

The application of stainless steel in paper making industry