Aplicação Em Indústria de Pulp& Paper - ÓTIMO

8/12/2019 Aplicao Em Indstria de Pulp& Paper - TIMO

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Duplex America 2000 Conference

Stainless Steel World

2000 KCI Publishing BV

DA2_061

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Increased usage of duplex materials in manufacturing of pulpingequipment

Authors: Alpo Tuomi, (VP Marketing, Valmet Chemical Pulping Oy, Finland), Allan Lfstrand, (Managing Director,

Sunds Defibrator Pty Ltd, South Africa) and Mikko Harju, (Welding Engineer, Metso Corporation, Pori Works, Fin-

land)

1 Introduction

In many industrial areas, chemical pro-cesses are developing in a direction whichis setting ever-increasing demands also onthe construction materials of the equip-ment. This same development has takenplace in the pulp and paper industry. Thedevelopment of pulp and paper processes

has been closely linked to the developmentof stainless steels and both industrial sec-tors have strong connections in the Nordiccountries. Due to demands from the earlypioneers in the pulp and paper industry inthe Nordic countries and the constantsearch for better acid-resistant materials,the stainless steel industry in the Nordiccountries was born and has become aworld leader in this field.Experience in this field goes back manyyears and suppliers have been involved in

replacing pulp digesters made of a rivetedcarbon steel construction and in the case ofthe sulfite industry, vessels lined with acidproof bricks. The next step was a processwhere old digesters were lined internallywith approximately 3mm stainless steelsheets held by a vacuum system betweenthe parent metal and the liner. In somecases the digesters were strip-lined with

150mm wide stainless steel strips. This wasa mammoth task which, however, served itspurpose since there was really no otherway, and solid stainless steel vessels wereout of the question in those days due to thehigh prices of heavy wall thicknesses.Later on solid stainless steel vessels havereplaced digesters manufactured from cladsteel material. The introduction of the

Avesta cold-stretching method made itpossible to manufacture solid stainlesssteel vessels with 4050% lower wall thick-ness thereby being price competitive withstandard solid stainless steel vessels. How-

EOP DI

D0 DII

Oxygen delignification

Bleaching

BalingPulp drying

Debarking Chipping Cooking

Deknotting

Screening

Washing

Reclaiming

Rescreening Cutter

Figure 1. A flow sheet of a typical pulping process.

Material Price factor

304L 1

316L 1.3

2304 1.5

2205 1.6

317L 2.3

2507 3.0

904L 3.4

254 SMO 4.7

654 SMO 7.5

Table 1. Relative fabrication material prices.
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Figure 2. Usage of duplex material in a modern pulping line.1 Solid duplex material2 Vats and conveyor screws, or even totally of duplex3 Upper shell parts

Figure 3. Wall thickness of a digester when fabricated of different materials, design temp. 204C, pressure 13.5 bar.


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In kraft pulping substantial savings can be

achieved when using duplex 2205 material,taking into consideration the differentcodes (in this case the ASME Code and theSwedish Pressure Vessel Code (TKN)). Ascan be seen, a saving of 50% in materialthickness is achieved compared to usingsolid carbon steel and a slightly lower sav-ing as regards the austenitic grades.Figure 3 shows the material savings inbatch digester fabrication for kraft pulping.According to the Avesta survey, September98, altogether 114 digesters, including

both continuous and batch digesters, havebeen fabricated of duplex material (table 3).As a conclusion, the following differences indigester wall thickness can be achieved:

Duplex digester wall 76% of solid 304 wall (ASME) 54% of solid 304 wall (TKN) 79% of clad steel wall (ASME) 68% of clad steel wall (TKN)

The biggest batch digesters made fromduplex 2205 are 400m

3 which today is our

standard size for new digesters.Figure 4shows a 400m

3 batch digester under fabri-cation (Metso Pori Works, Finland).Pressurized vessels in general, manufac-tured by our company, vary from 400 to1100m

3 and the wall thickness variesbetween 4 and 30mm.

2.2 Washing and screening

Single pieces of process equipment, suchas pulp washers and presses, have tradi-tionally been manufactured of various stain-

less steel grades, but today duplex

materials are increasingly used even for

fabrication of parts of those.In kraft pulping, water quality and thedegree of process closure are the majorinfluences on the environment in brownstock washing. Corrosion rates of morethan 5mm on carbon steel have beenreported. Depending on pH control, duplexsteels are proving to be the most suitable.Duplex materials are typically used todayalso in the fabrication of filter drums andpulp conveyor screws. In big modern pulp-ing lines wash presses are, however,

increasingly being used instead of tradi-tional drumfilters. The TwinRoll press(figure 5) isa typical washing apparatus.Earlier press vats were typically made ofduplex material, today even all parts of cer-tain press types are fabricated of duplex.Just recently we have also started to fabri-cate traditional drum washers from duplex.Figure 6 shows a duplex vacuum washerdrum in the workshop.

2.3 Oxygen delignification

The majority of O

2 stages operate at

medium consistency and 316L has gener-ally been used as the fabrication material.SAF 2205 is constantly gaining ground atthe expense of other grades. Today almostall O

2 reactors made by our company are ofduplex 2205 as well as all the batch digest-ers. According to the Avesta survey of 1998,various pulping equipment suppliers in theworld have so far fabricated totally 107 oxy-gen reactors of duplex material. Figure 7.

2.4 Bleaching

Besides a similar type of reactors andwashers as in the preceding process

Figure 5. A TwinRoll press used for pulp washing. Figure 6. A vacuum washer drum made of duplex.


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The pressure vessel codes used so far forfabrication have been:

SFS (Finnish requirements), based onGerman code

ASME Code TKN (Swedish code) ADM (AD Merkblatt, German code)

Plate materials used depending onrequirements have been:

W. 1.4462 AD W2 + VdTV Wb 418 ASME SA 240 S31803 Avesta Sheffield 2205 PKVP-03.155

Rev. 2

Edge preparation for shell plates is made bymachining. Double-V or double-U groovesare used depending on the material thick-ness. Careful edge preparation helps keeprepair costs low.

Semi-spherical and elliptical heads deliv-ered in segments are ordered as coldformed without annealing. The sub-suppliermakes edge preparation and pre fit-up.Material thickness of vessel shells has been4 to 40mm. This makes submerged arcwelding (SAW) an attractive process formost longitudinal and circumferential weldseams of shell and major nozzles. Otherpressure-retaining parts are welded usingthe shielded metal arc process (SMAW), seefigure 4. For some non-pressure-retaining

parts flux-cored arc welding (FCAW) isused.Welding instructions (WPS) shall be basedon welding procedure tests. For 2205 mate-rial the control of heat input during weldingis necessary to avoid reduction of corrosionresistance and toughness of the weldedjoint. The allowable range depends on thecase but normally it is 1.0 to 2.5kJ/mm. It isrelatively easy to keep within that rangewhile most of the welding is flat position.Documented spot checking helps the weld-ers to keep in mind that it is important to fol-low the welding parameters given in WPS.The number of necessary welding produc-tion tests depends on the requirements ofeach code. So far we have not met anyproblems in fulfilling the test requirements.

The qualifications of welders and plateworkers for 2205 work shall always containa theoretical part even if they are alreadyfamiliar with austenitic stainless steel work.One can pass the welding test but still makeexpensive mistakes in actual work. Qualifi-cation tests should be done using 2205base and filler material even if the qualifica-tion standard allows using austenitic mate-rial.The quality control of a 2205 pressure ves-sel is based on a quality plan made soon

after the order. The NDE methods based onthe code used are visual (VT), dye penetrant(PT) and radiographic examination (RT).All the welds are examined visually 100%.PT can be 100% for all nozzle to shell welds(ASME) or 25% of shell weld seams and10% of nozzle and fillet welds (ADM). Typi-cal examination RT is 100% for longitudinalwelds and 25% (ADM) or spot (ASME) forcircumferential welds. The percentage ofrejected X-ray films is used for measuringwelding quality. This figure has been lessthan 2% during the past few years, which

has been considered acceptable.

Figure 9. Delivery of duplex digesters for Riau Andalan Pulp &

Paper, Indonesia.

Ahlstrm 1

Beloit 15

Kvrner 5

Sunds 83

Other 10

Total 114

Table 3. Duplex digesters fabricated until 1998.


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4 Conclusions

SAF 2205 with its high strength and corro-sion/erosion properties is becoming morepopular. It can often be justified on a costbasis. Wall thickness reductions of 50% oncarbon steel and 35% on clad steel can beachieved. A kraft pulping process includesa large number of pressurized reactors andatmospheric large tanks and towers, as wellas various main equipment. Total savingsachieved through favorable characteristics

of duplex materials are huge, consideringthat a total cost of an average fiber lineequipment delivery can be up to MUSD100.

References

1 Committee of steel producers of AISI; stainlesssteel for pulp and paper manufacture.

2 Conference paper, Basil Goldswain, AllanLfstrand, Application of Stainless Steels in thePulp and Paper Industry, TAPPSA 1997, Durban,South Africa.


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