3_niro standard 2.04

8/2/2019 3_Niro Standard 2.04

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Standard 2.04

1998-10-01 Surface Treatment - Stainless Steel Sheet/Plate /5

Niro A/SNiro A/S · Gladsaxevej 305 · PO Box 45 · DK-2860 Soeborg · Denmark · Tel +45 3954 5454 · Fax +45 3954 5800 · Reg No 12682

Contents Page

1. Preface.........................................................................2

2. Indications on drawings.............................................3

3. Surface t reatment of the welding zones...................4

4. Surface t reatment of the general surface .................5

Surface TreatmentStainless Steel Sheet /Plate



Standard 2.04

1998-10-01 Surface Treatment - Stainless Steel Sheet /Plate /5

Niro A/S

1. Preface

1.1 Scope

This standard applies to equipment surf acesof stainless steel sheets or plates. It specif ies

the standardized surface treatments anddef ines the corresponding symbols for useon technical drawings.

Requirements of any other surfacetreatment shall be completely specified onthe drawings.

1.2 Plate/sheet f inish

Unless otherwise specified, the followingplates/sheets shall be used (see EN 10088-2):

Plate thickness£ 6 mm: 2B or 2D

Plate th ickness > 6 mm: 1D

Finish 2B is preferred. The select ion o fplate/sheet type shall be consistent, i.e. amix of 2B and 2D shall not be used for t hesame component .

Exact values for roughness are not available,as they vary from mill t o mill f or t hedifferent thickness of sheet/plate. Average

surf ace roughness within t he fol low ingranges can usually be expected:

2B: Ra = 0.1 to 0.5 mm

2D: Ra = 0.2 to 1.0 mm

1D: Ra = 2 to 8 mm

If part icular small values of roughness arerequired, ground or poli shed plates shouldbe specified (e.g. 2G and Ra/Rz).

1.3 Scratches etc.

Scratches on the sheets/plates larger t han 30mm shall be removed by spot grinding.

Grinding zone shall be rectangular andparallel to the vertical/horizont al axis of theequipment.

The grinding zone shall be demarcated w ithtape on all sides. Minimum distance fromscratch t o t ape: 25 mm. Tape to be removedafter grinding.

Roughness after grinding:

Ra £ 1.0 mm, Rz £ 10 mm

1.3 Carbon steel contaminat ion

In case of contamination with carbon steel,the affected area(s) shall be

decont aminated (preceding gr inding maybe necessary).

Decontamination is typically carried out byusing a 2-10% nit ric acid solu t ion. The t imefor decontamination depends on thetemperature, acid solut ion, and t he amountof carbon steel to be removed.

Thorough degreasing/cleaning of thesurface for lubricants, grease, glue etc. isrequired prior t o the treatment.

Decontamination will not give an actualpassivation of the steel.

1.4 Welding qualit y

In general the welding qualit y shall be inaccordance with Niro Standard 1.4-, unlessotherw ise specif ied.

Proper gas protection is required duringwelding. Aft er welding the heat affected

zone on t he root side shall have ayellowbrown or lighter colour. On thewelding side it shall have an even colourand must not be black.

If the colour is darker than specified above,pickling shall be made without any extracosts to Niro, even if such pickling is notspecified.

1.5 Equipment appearance

The f inal equipment shall always have a

unif orm appearance, i.e. number ofscratches/repairs must be l imit ed. In case ofextensive repairs, Niro reserves the r ight toreject the equipment or part s hereof.



Standard 2.04


Niro A/S

2. Indication on draw ings

2.1 Types of surfaces

Type of surface treatment depends on thetype of surface to be treated, i.e.:

· Product contact surfaces

· Non-product contact surfaces

Usually the int ernal surf ace wi ll be thesurf ace in cont act w ith the product .

For both t ypes of surfaces dif ferentt reatments wi ll normally be specif ied for thewelding zones and the general sheet/platesurface.

2.2 Symbol ic indication on draw ings

The symbols (table 1) are used t o specifydif ferent combinations of surf ace treatmentrequirements. The symbols shall be statedabove the tit le block of the drawing.

Normally two treatment symbols are used:

· First symbol for t he int ernal surf ace

· Second symbol for the external surf ace.

Example of ind icat ion: T2/T3.

T2: Internal welding zones to be ground.No treatment of the general internal

surf ace requi red.

T3: External welding zones to be pickled.No treatment of t he general externalsurf ace requi red.

If necessary, the surface treatmentrequi rements may be specif ied by indicatinga symbol f or each surface. This shouldpreferably be done on a separate f inishdrawing.

Requirements for the different treatmentsare specified in section 3 and 4.

2.3 Other indicat ions

In case part icular small roughness values arerequired, maximum values for roughnessshall be stated.

Roughness parameters Ra and Rz arepreferred.

Type ofsurface

Symbol Welding zone General surface

T0 Brushed Untreated

T1 Pickled Untreated

Internal T2 Ground Untreated

P2Ground andpassivated

Untreated(passivated)

T3 Pickled Untreated

T4 Pickled Glass blasted

External T5 Ground Oil ground

T6 Untreated Untreated

T7 Brushed Untreated

- T8Electrolyti c polishing(pre-t reatment to be specif ied)

Table 1 - Surf ace treatment symbols



Standard 2.04

1998-10-01 Surface Treatment - Stainless Steel Sheet /Plate /5

Niro A/S

3. Surf ace t reatment of t he w elding zones

3.1 Untreated - T6

No treatment required.

3.2 Pickled - T1, T3 and T4

Slags, spat ter and the most coarse oxides tobe mechanically removed, followed bypickling in a 50-60 mm wide zone centeredaround the weld.

Prior t o pickling t he surf aces shall bethoroughly degreased/cleaned in order toremove lubricants, grease, glue etc.

A ni t ric acid / hydrof luoric acid based

pickling compound should be used. Picklingcompounds containing hydrochloric acidshall not be used.

The eff ect iveness of the pickling dependson t he pickling compound and thetemperature of the steel.

Correct pickling will give a metallic cleansurf ace wit hout remains of heat oxidizingor slags.

As a principal rule i t is not necessary to carry

out passivation or decont amination afterpickling.

3.3 Brushed - T0 and T7

Brushing of the weld and the heat af fectedzone (HAZ) with parallel traces in thelongit udinal direction of t he weld.

The treated zone shall be centered aroundthe weld and shall be reasonably st raightand uniform, i.e. wit hin ± 5 mm of the

average widt h.

Af ter t reatment t he surf ace shall be metallicclean without any discolorat ion, slags,spat ter etc.

3.3 Ground - T2 and T5

Grinding with parallel grinding traces in thelongitudinal direction of the w eld in a 50-60

mm wide zone centered around the weld.

Before grinding, the grinding zone shall bedemarcated w ith tape on all sides.


Ra £ 1.0 mm, Rz £ 10 mm

3.5 Ground and passivated - P2

Grinding in a 50-60mm wide zone centeredaround t he weld as described in sect ion 3.3followed by passivation of the grindingzone.

As it is not possible to remove heatoxidizing, slags etc. by passivation, thesurfaces shall be metallic clean pr ior to t hetreatment. Lubricants, grease, glue etc. shallbe completely removed.

A passivation compound is based on a purenit ric acid solut ion w ith a concent ration ofnit ric acid larger than 18% (mass).

Improved corrosion resistance is obtained bypassivation, as the natural surface layer ofchrome oxides is strengthened and possiblecarbon steel cont aminat ion is removed.



Standard 2.04


Niro A/S

4. Surface treatment of the general surface

4.1 Untreated - T1, T2, T3, T6 and T7

No treatment required.

4.2 Untreated and passivated - P2

No treatment required, but in case ofsurface repairs, e.g. scratches, the repairedareas shall be passivated (see item 3.5).

4.3 Glass blasted - T4

Glass blast ing of the ent ire surf ace requi red.Surface treatment of welding zones shall befinished prior to glass blasting.

This treatment will give a metallic, greysurface wit h visible welds. Glass blast ingcannot replace pickling or passivation of theheat oxidizing zones.

The supplier shall ensure a correct workingprocedure regard ing size of nozzle, distancefrom nozzle to surf ace, time of exposureand other parameters inf luencing the result .The fo llow ing requirements apply:

· Whole glass balls in the size range 100-200 mm to be used.

· Max. 15% of the balls must be damagede.g. lose their roundness

· No contamination of the blow ing mediaby other part icles, e.g. carbon steel.

· Blow pressure ³ 4 bar.

· Angle of attack between blow ing mediaand surface ³ 30°.

· Degree of coverage shall be between 200and 300%.

The glass balls and the size of same shall betested frequently by sieve analysis, e.g.according to MiL-S-13165 B.

Other blow ing media (e.g. ceramics) mayonly be used, if accepted by Niro.

Af ter the t reatment the surf ace shall meetthe f ollow ing requirements:

· Homogenous appearance.

· Ra £ 2.0 mm, Rz £ 20 mm.

· Cleaned for loose glass particles· Free f rom “ black f ingers” (e.g. by

spraying w ith a suit able oil), dirt etc.

4.4 Oil ground - T5

Oil grinding of the ent ire surf ace required.Surface treatment of welding zones shall be

fin ished prior to this treatment.

The purpose of t he treatment is to give thesurface a uniform half-mat appearance, forexample by one of the following methods:

A. Oil grinding using a grinding w heel w ithemery cloth lamella.

B. Grinding using a grind ing w heel w ithf iber lamella possibly w ith addit ion ofgrinding paste.

C. Oil grind ing using a cont inuous grindingbelt while the component rotates.

Grinding t races on the surf ace have to beminimal and reasonably parallel. Slight lyvisible grinds at w elding zones.


Ra £ 1.0 mm, Rz £ 10 mm

4.5 Electrolyt ic poli shing - T8

Electrolyt ic polishing of the ent ire surf acerequi red. Possible surf ace t reatment ofwelding zones shall be f inished prior t o thistreatment.

This treatment w ill give a metallic, brightsurf ace. If welds shall be invisible after thetreatment, grinding to Ra £ 0.3 mm isrequired prior to electro-polishing. This shallbe specif ied on t he drawing.

The roughness of the surf ace af ter the

electrolyt ic polishing depends on theroughness of the surf ace prior to t reatment.The treatment is expected to give aroughness which is a lit tle better than theoriginal roughness.

3_niro standard 2.04

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