Technisch Infoblad #35
Alle verzinkerijen in de Benelux volgen de eisen van de internationale kwaliteitsnorm EN-ISO 1461. Af en toe wordt er voor buitenlandse opdrachten gevraagd te voldoen aan de Amerikaanse verzinkersnorm ASTM A 123. Beide normen zijn volledig onafhankelijk van elkaar opgesteld en gereviseerd in de loop van vele jaren. In beginsel is het proces van thermisch verzinken niet anders in de USA als in de EU. Dus het verzinkte product zal niet van elkaar afwijken, alleen de normtekst wijkt af. Voor inkopers die niet zeker zijn van hun zaak, is dit een struikelblok en houden ze vast aan de ene of de andere norm. Dit document maakt een vergelijking tussen beide normen. Zo wordt duidelijk waar men voor ASTM-
opdrachten extra dient op te letten.
In onderstaande tabel 1 wordt de vergelijking tussen de EN ISO 1461 en de ASTM A123 in detail weergegeven. Daarbij moet worden opgemerkt dat hoofdstukken en paragrafen geheel anders van opzet zijn en dat om die reden de verschillen per item worden gerubriceerd. Daarna worden enkel de punten beschreven waar de ASTM A123 extra eisen stelt afwijkend van de ISO 1461.
De verschillen worden in de Engelse taal weergegeven om deze te kunnen delen met partijen die de Nederlandse taal niet beheersen.
| ITEM | EN-ISO 1461 | ASTM A 123 |
|---|---|---|
| Scope | general properties and test methods iron and steel articles fabricated not if continously galvanised not tube & pipe if automatic galvanised not products with specific standards not after - treatment not over-coating also centrifuged | requirements zinc coating test methods iron and steel products fabricated and unfabricated not wire, pipe & tube sheet if continously galvanised not tube & pipe if automatic galvanised not steel < 0,76 mm thickness not centrifuged (A153) |
| General requirements | content of zinc melt not chemical composition basis metal not surface condition basis metal | content of zinc melt chemical composition, grade or designation and type and degree of surface contamination of basis metal shall be supplied by purchaser not surface condition basis metal |
| Bath | total other elements <=1,5 mass% (excl. Tin and Iron) ISO 752, EN 1179/EN 13285 | not less than 98 % zinc by weight |
| Construction | according to ISO 14713-2 | according practices A143, A384, A385 |
| Additional info by the purchaser | composition and properties of basis metal presence of flame (laser, plasma)-cut surfaces indication of significant surfaces Identification of significant surfaces identification where unevennes are unacceptable written evidence of internal vents necessity of sample special pretreatment requirements necessity of special thickness after-treatments / over-coatings inspection arrangements | chemical composition, grade or designation and type and degree of surface contamination of basis metal shall be supplied by purchaser The method of selection and number of test articles shall be agreed upon (sampling plan (B602)) necessity of special coating thickness special test requirements surface condition of articles to be painted necessity of the use of masking materials leave the uncoated areas untreated in case of paint appearance criteria for Architecturally Exposed Structural Steel (AESS) any other project-specific aesthetic requirements |
| Info by the galvaniser | upon request: method of renovation uncoated areas certificate of compliance (ISO 10474) certificate of quality assurance | upon request certificate of compliance |
| Safety | to be provided by purchaser sufficient number of venting holes sufficient number of draining holes give consent to galv to provide holes | |
| Acceptance inspection | before products leave galvanizer assessment of appearance testing of thickness (if required by customer) adhesion test only by agreement. There is no suitable standard | by galvaniser or purchaser material shall be inspected at the galvanizer’s plant prior to shipment. Or otherwise by agreement assessment of appearance testing of thickness The specifying of tests for adhesion and embrittlement shall be subject to mutual agreement |
| Sampling thickness test | inspection lot = single order or single delivery load minimum # of articles see table 1 (identical to A 123) | inspection lot = single order or single delivery minimum # of articles see table (identical to ISO 1461) |
| Appearance | distance from > 1m free from; a. blisters (i.e. raised areas without solid metal beneath), b. roughness and sharp points (if it can cause injury), c. free from uncoated areas. considerations to aesthetics are secondary Agreement No cause for rejection; a. occurrence of lighter or darker areas b. some unevenness (e.g. Orange peel) c. Wet storage stain (if coating thickness still meets minimum value) d. Aesthetic effects (weld seepage) flux residues and zinc ash shall be removed where they can affect the intended use of the article or its corrosion resistance requirement (unless access in restricted). | Upon shipment from the galvanizing facility, galvanized articles shall be free from uncoated areas, blisters, flux deposits, and gross dross inclusions. Lumps, projections, globules, or heavy deposits of zinc which will interfere with the intended use of the material will not be permitted. Marks in the zinc coating caused by tongs or other items used in handling the article during the galvanizing operation shall not be cause for rejection appearance criteria for Architecturally Exposed Structural Steel (AESS) |
| Thickness measurement | test method accordingly ISO2808 & 2178 magnetic flux path method in case of dispute, gravimetric test magnetic method possible alternative : microscopic cross section not on cut surfaces not on areas < 10 mm from edges not on areas < 10 mm from flame-cut surfaces not on areas < 10 mm from corners | test method accordingly Practice E376 in case of dispute, magnetic test magnetic method possible alternative : stripping method / weighing before and after galvanising / microscopic cross section (=gravimetric test) |
| Reference area | number depending on shape & size of articles minimum three reference areas position depending on shape & size of articles 100 mm from edges Long articles: 100 mm from each end and in the middle whole cross section of the article Reference area at least 10 cm² minimum five test readings per area | minimum three reference areas widely dispersed over the volume of the specimen minimum five test readings per specimen |
| Thickness | mean coating thickness >= mean coating thickness table 3 and 4 mean value over ref area >= local coating thickness table 3 and 4 if not conform, 2x number of test articles | average coating thickness of all specimens > average table 1 average coating thickness of single specimens > average table 1 Minimum average thickness of coating for any individual specimen is one coating grade less than that required if not conform, 2x number of test articles individual measurement no cause of rejection |
| Renovation | total uncoated areas < 0,5% total surface of article each uncoated area < 10 cm² if larger, re-galvanize; Renovation; by zinc-rich paint, zinc-flake or zinc-paste products. Otherwise by zinc-alloy stick or by thermal zinc spraying including removal of scale, cleaning and pretreatment thickness of renovated areas ≥ 100 μm | total uncoated areas < 0,5% total surface of article or 256 cm²/ton each uncoated area < 25 mm in de kleinste dimensie length and width of the uncoated area shall be allowed to exceed 1 in[25 mm] in only one of the two dimensions. Surface conditions related to deficiencies related to design, detailing, or fabrication as addressed by Practice A385/A385M shall not be grounds for rejection. by zinc-rich paint Methods according to practice A780/A780M thickness minimum 75 μm and maximum 100 μm |
| Adhesion | no suitable standards exist does not need to be tested any test should be agreed prior to start if tests, only in significant areas cross-hatch test is more demanding than required | by cutting or prying with a stout knife no flaking off any test should be agreed prior to start |
| Embrittlement | not mentioned. Part of EN-ISO 14713-1 | only if evidence is present in accordance with Practice A143 |
| Certificate | upon request additionally certificate quality assurance (ISO9001) | upon request |
VISUELE EIGENSCHAPPEN VAN DE VERZINKTE STUKKEN
In de ISO 1461 wordt gesteld dat het primaire doel van verzinken een bescherming van het staal tegen corrosie is. Indien extra esthetische of decoratieve eisen noodzakelijk zijn, dient de klant de graad van nabewerking met de verzinker af te spreken. In de ASTM A123 wordt er niet over esthetische eisen gesproken. Er dient dus maximaal gelet te worden op het gebruik van de materialen.
Het optreden van donkere of lichtere grijze plekken of enige oneffenheid op het oppervlak is voor de ISO 1461 geen reden voor afkeur; ook witte vlekken die door het opslaan zijn veroorzaakt ( witte roest) zijn geen reden voor afkeur zolang de zinklaagdikte boven het gespecifieerde minimum blijft. Esthetische problemen te wijten aan niet volledig gesloten lassen zijn eveneens geen reden voor afkeur. Ook over deze punten wordt er in de ASTM A123 niets gezegd. Dit dient dus voor opdrachtbevestiging met de klant afgesproken te worden.
De ASTM A123 definieert volgende extra eisen :
Materialen mogen niet aan elkaar kleven na het afkoelen. Het zinkoppervlak mag niet afbladeren bij normaal gebruik. Er dient dus bij de uitgangscontrole speciaal aandacht gegeven te worden aan de montagegaten, de draadcontacten en het zinkoppervlak bij Si-rijk materiaal.
EISEN NAAR ZINKLAAGDIKTE
Het meten en de manier van meten van de zinklaagdikte is nagenoeg identiek in beide normen. Er is enkel een verschil in de vereiste zinklaagdikte (zie tabel 2). “Local coating” en “Average one” heeft dezelfde betekenis : het gemiddelde van de 5 metingen in een referentiegebied. “Mean coating” en “Average all” heeft eveneens dezelfde betekenis: het gemiddelde van alle metingen.
| 1461 | A123 | ||||
|---|---|---|---|---|---|
| Local coating | Mean coating | Average one | Average all | ||
| Steel (ISO1461) Structural shapes (A 123) | ≥ 6,4 mm >6 mm tot < 6,4 mm >4,8 mm tot ≤ 6 mm ≥3,2 mm tot ≤ 4,8 mm >3 mm tot <3,2 mm ≥1,6 mm tot ≤ 3 mm ≥ 1,5 mm tot <1,6 mm <1,5 mm | 70 70 55 55 55 45 45 35 | 85 85 70 70 70 55 55 45 | 85 65 65 65 60 60 35 35 | 100 75 75 75 65 65 45 45 |
| Pipe&tubing (A 123) | ≥ 6,4 mm >6 mm tot < 6,4 mm >4,8 mm tot ≤ 6 mm ≥3,2 mm tot ≤ 4,8 mm >3 mm tot <3,2 mm ≥1,6 mm tot ≤ 3 mm ≥ 1,5 mm tot <1,6 mm <1,5 mm | 70 70 55 55 55 45 45 35 | 85 85 70 70 70 55 55 45 | 65 65 65 65 35 35 35 35 | 75 75 75 75 45 45 45 45 |
| Steel (ISO 1461) Strip/Bar/Plate (A 123) | ≥ 16mm ≥ 6,4mm tot < 16mm >6mm tot < 6,4mm >4,8mm tot ≤ 6mm ≥3,2mm tot ≤ 4,8mm >3mm tot <3,2 mm ≥1,6mm tot ≤ 3mm ≥ 1,5 mm tot <1,6 mm <1,5 mm | 70 70 70 55 55 55 45 45 35 | 85 85 85 70 70 70 55 55 45 | 85 65 65 65 65 60 60 35 35 | 100 75 75 75 75 65 65 45 45 |
| Casting | ≥ 6,4mm ≥6mm tot < 6,4mm >4,8mm tot < 6mm ≥3,2mm tot < 4,8mm >3mm tot <3,2 mm ≥1,6mm tot ≤ 3mm ≥ 1,5 mm tot <1,6 mm <1,5 mm | 70 70 60 60 60 60 60 60 | 80 80 70 70 70 70 70 70 | 85 85 85 65 60 60 35 35 | 100 100 100 75 65 65 45 45 |
EN ISO 1461
Door thermisch verzinken aangebrachte deklagen op ijzeren en stalen voorwerpen - Specificaties en beproevingsmethoden.
ASTM A123
Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products
