ADDING VALUE TO STEEL, SINCE 1965
| T: +27 11 456 7960 | F: +27 11 450 0728 | E: hdgasa@icon.co.za

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+27 (0)11 456 7960

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HOT DIP GALVANIZING: RELIABLE, DEPENDABLE, PREDICTABLE, SUSTAINABLE

We are committed to delivering excellence

To position the Hot Dip Galvanizers Association of Southern Africa, comprising all its Members and other interested parties, as a professional organization serving the interests of all parties dependant upon the hot dip galvanizing industry. To develop and expand the demand for hot dip galvanizing, identify and develop new market opportunities for the benefit of Members and other Stakeholders.

About the Hot Dip Galvanizers Association

The Hot Dip Galvanizers Association Southern Africa (HDGASA) is a not-for-profit trade association dedicated to serving the needs of specifiers, architects, engineers, contractors, fabricators and hot dip galvanizers throughout Southern Africa.

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Members

Provides free technical advice to members relating to their galvanizing plant, equipment, process controls, environmental protection and waste minimisation. Offers training in numerous aspects related to hot dip galvanizing, some of which are only available to members.

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TECHNICAL

The association is a technical information center. Please use this link on our website to access information sheets, codes of practice, steel protection guides and to view case studies. These are at the disposal of specifiers, architects, engineers,  contractors, fabricators and hot dip galvanizers to inform about the benefits of hot dip galvanizing.

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Publications

The Association is proud to announce that all the back issues of Hot Dip Galvanizing Today are available for download in PDF format. Please note that some of the files are of a large size and will take a few minutes to download.

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Awards

Presented annually, these awards represent the finest accomplishment in the use of hot dip galvanizing. For each category award, all project partners are considered winners as the nature of hot dip galvanizing is a combined effort, with the final project reflecting the work of many.

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Useful Links

Our Association partners with many professional bodies and Associations.

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PRODUCTS AND SERVICES

Provide technical assistance to end users, consultants and fabricators as to the appropriate application of hot dip galvanizing and duplex coating systems for corrosion control of carbon steel. Technical assistance and services are provided by means of presentations, inspections, setting of specifications and the provision of training.

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Presentations

The Association is a technical information centre established for the benefit of specifiers, consultants, end users and members. Contact the Association should you require a comprehensive presentation on various aspects of hot dip galvanized coatings including,

  • Introduction to Corrosion
  • Duplex Coatings (zinc + paint)

The contents of the presentation can be tailored to suit the requirements of the audience.

Inspections

The HDGASA will carry out inspections wherever required for members and their customers.

Technical Evaluations

Provide training and education for member companies to ensure a high standard of quality and service throughout the hot dip galvanizing industry.

Galvpatch®

Galvpatch is a zinc rich epoxy used for site repairs on hot dip galvanized components.

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Metal Pro Galvanized Steel Markers

The marker is a soluble ink based marker used for component manufacture in the fabrication process.

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Training

Hot dip galvanizing is one of the most widely used methods of protecting steel from corrosion.  During fabrication and after hot dip galvanizing, the coating is inspected for compliance with the relevant specifications.

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Course Schedule

2016 course dates for Introduction to Hot Dip Galvanizing and Certified Inspectors Course Level II

COURSE SCHEDULE

Membership

Provides free assistance to members with respect to quality aspects during fabrication, hot dip galvanizing and site inspections. The Association will investigate and objectively report on coating quality issues without compromising its creditability or professional reputation.

Offers technical advice relating to specifications, steels suitable for hot dip galvanizing and the optimum corrosive control measures to suit various environments.

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CASE STUDIES

The following case studies are most relevant to South African weather conditions and climate. Please click the links below to obtain further details.

Volume 12, Issue 2: September 2015 (61)

  1. Intergalva 2015: The Global Galvanizing Awards.
  2. Report on Intergalva 2015
  3. Forms of Corrosion: Corrosion due to incorrect selection of materials
  4. Forms of Corrosion: White rust and wet storage stains
  5. Bob’s Banter: The role of mathematics education in industry
×

Volume 12, Issue 1: May 2015 (60)

  1. Hot DipGalvanizing: A cost effective protection system.
  2. Advertorial:How to achieve savings and a better galvanizing finish with nickel tablets
  3. Rail Fasteners:Performance of hot dip galvanized resilient rail fasteners exposed in a severe marine environment
  4. Reinforcing in Steel: Shouldn’t more rebar be galvanized?
  5. Soil side corrosion
  6. High Strength Bolts:The use of high strength bolting assemblies for pre-loading
  7. Understanding Distortion
  8. Case Study:The performance of Pandrol rail fasteners in a marine environment on the Natal South Coast
  9. Bob’s Banter: Doublespeak
×

Volume 11, Issue 3: November 2014 (59)

  1. Projects in the Spotlight: Kirstenbosch Tree Top Walkways.
  2. Projects in the Spotlight: Redevelopment of the Tramways Building, Port Elizabeth
  3. Projects in the Spotlight: New Military Health Base Depot
  4. Projects in the Spotlight: The Last Glass House–new residence in Parktown
  5. Projects in the Spotlight: The Druenberg Solar Power Project
  6. Projects in the Spotlight: Blast protection covers at Syferfontein
  7. Projects in the Spotlight: Cellular towers at Cell C Headquarters in Midrand
  8. Projects in the Spotlight: Conveyor river bridges.
  9. Projects in the Spotlight: Uzizi Pedestrian Bridge in the Tugela Ferry District
  10. Projects in the Spotlight: Beth Diane Armstrong; artist
  11. Projects in the Spotlight: New bulk liquid berth and floating breakwater
  12. Projects in the Spotlight: Transformer radiators for Eskom or local authority sub stations
  13. Projects in the Spotlight: Landing Platforms, Saldanha Bay
  14. Bob’s Banter: Achieving our desired future means managing the unexpected
  15. Conference: The use of hot dip galvanizing in mining in Southern Africa (part 3)
  16. Opinion:General galvanizing–how does SA compare globally? (part 2–technology)
  17. On the Couch…. With Mark Thomas and Henry Fagan
×

Volume 11, Issue 2: November 2014 (58)

  1. Conference: The use of hot dip galvanizing in mining in Southern Africa–part two
  2. Case Study: Eskom Coastal Sub – Stations
  3. Fasteners: Impala Bolt & Nut stays on top of the fastener market
  4. Fasteners:Fastener availability matrix and participating fastener suppliers
  5. General: POLASA fills dire need
  6. Education and Training: Three day Galvanizers Inspectors Course
  7. On the couch …Professor Albrecht Herholdt
  8. Technical: Galvastop – masking of components prior to hot dip galvanizing for the exclusion of the coating.
  9. Member’s Corner: The benefits of chossing zinc for corrosion protection seen from an unexpected source.
  10. Member’s Corner:Steel industry related app launched!
  11. Bob’s Banter: The psychology of health and safety
×

Volume 11, Issue 1: November 2014 (57)

  1. Conference: The use of hot dip galvanizing in mining in Southern Africa – part one.
  2. Case Study: Eskom Coastal Sub-Stations.
  3. Case Study: Bellville Transport Interchange upgrade built in 2002 stands the test of time.
  4. Duplex: Duplex coating good after 14 years of mild to moderate marine exposure.
  5. Poles & Masts: Leading steel pole manufacturer takes delivery of high-end CNC machines.
  6. Opinion: General galvanizing – how does SA compare globally? Part 1 – The Market.
  7. General: Effectively avoiding weld spatter dramatically increases the quality of the hot dipgalvanized coating.
  8. Technical: The difference between Hydrogen and Strain Age Embrittlement.
  9. Galvpatch successfully exposed to fridge conditions at minus 25ºC for 8 months
  10. Education and Training: Three day Galvanizers Inspectors Course
×

Volume 10, Issue 4: November 2013 (56)

  1. The World of Hot Dip Galvanizing around Us: American Galvanizers Association – Metrolina Greenhouses, South Campus Central Chiller Plant, Franklin Park Conservatory, Blast Deflectors, Brea Power Plant, Electric Vehicle Rail Tramway, Gibbs Street Pedestrian Bridge, Platt Street Bridge Restoration, Solaris Tower, The Christina and John Markey Memorial Pedestrian Bridge, Winged Glory, WinStar Casino Globe.
  2. The World of Hot Dip Galvanizing around Us: Galvanizers Association of Australia – Making the moment last long, High stakes skin for Star extension, Galvanized finish guards new rail work, From pit to prestige sport centre, Upholding very green park build.
  3. Duplex Coatings: Effective corrosion protection of structural steel
  4. General: Thermal Spray Association of Southern Africa (TSASA).
  5. Education: Three day Galvanizers Inspectors Course
  6. Education: Beware – Salt spray testing! Misleading accelerated corrosion tests
  7. Education: Accelerated test methods applied to zinc coatings in terms of SANS 14713 – 1:2011
  8. Education: Guide to hot dip galvanizing for sustainable design
  9. General: Letter to the Editor
  10. On the Couch …. Robert JW Brusse
  11. Members News: The Advanced Roof and Building Technology Foundation
  12. Members News: What passivation is in practice and what it is not
  13. Members News: Fresh dynamics at Cape Galvanising Consolidated
  14. Members News: Transvaal Galvanisers
  15. Members News: ArcelorMittal involvement in Solar and LSF (Light Steel Frame) Projects
  16. Bob’s Banter: Achieving our desired future means managing the unexpected
×

Volume 13, Issue 1: April 2016 (62)

  1. Metallurgical investigation into the origin of cracks at welded connections on a hot dip galvanized
    fabricated structural steel perimeter walkway platform.
  2. Galvanizing of steel – all around us.
  3. Design considerations: venting and drainage
  4. Materials of Construction
  5. Purlins manufactured from hot dip coil
  6. Bob’s Banter: What a disappointment – there are no black holes!
  7. Case Study – Rural Pedestrian Bridges
  8. Personality Profile – Bob Wilmot
  9. 2016 Annual Golf Day
×

APPEARANCE OF SODIUM DICHROMATE

1. APPEARANCE OF SODIUM DICHROMATE

What is this?

A small amount of Sodium Dichromate is generally added to the quench water bath for passivation.

Cause

Although the recommended quantity of Sodium Dichromate is about 0.15 to 0.3%, occasionally when topping up, more is added.  This often results in a dark yellow to brown colour on the galvanized surface.  The darker colour will provide enhanced initial corrosion protection.

Effect / Remedy / Responsibility

This can be accepted since there is no adverse effect on corrosion control.

The galvanizer should maintain the concentration of Sodium Dichromate at about 0.15 to 0.3%.

×

2-ASH-DEPOSITS

2. ASH DEPOSITS

What is this?

Ash deposits are grey, non-metallic deposits consisting of zinc oxide that have been deposited on the hot dip galvanized coating.

Cause

Zinc oxide deposits can take place when the component is dipped or when it is removed from the bath.

Effect / Remedy / Responsibility

This can be accepted or negotiated dependent on functional requirements since the coating is normally intact underneath the ash deposits.  If required, ash must be removed by the galvanizer and the coating thickness verified for conformance to the specification requirements.

In the case of liquid conveyance pipes, all ash should be removed.

×

3-BARE-SPOTS

3. BARE SPOTS

What is this?

Although excluded from SANS 121:2011 (ISO 1461:2009), bare spots of about 5mm2 (2.2 x 2.2mm), due to small localised flaws, are adequately protected by the sacrificial properties of zinc and will have very little effect on the service life of the coating. 

Cause

There are several causes of bare spots.  These include:

Effect / Remedy / Responsibility

Where necessary, such spots may be repaired using one of the specified repair methods.  Gross uncoated areas are a cause for rejection.

The galvanizer should avoid overdrying and maintain the correct level of aluminium content in the kettle.

×

4-BLASTING-DAMAGE

4. BLASTING DAMAGE

What is this?

Sweep blasting (done correctly) substantially increases paint adhesion and final coating appearance.  However, done incorrectly it can result in coating damage.

Cause

Incorrect nozzle pressure; nozzle angle; sweeping distance; size of abrasive and recycling of grit.

Effect / Remedy / Responsibility

This is cause for rejection as a hot dip galvanized coating will be partially or fully destroyed by excessive blasting.  Refer to the HDGASA Code of Practice.

×

5. BLOWOUTS

What is this?

Staining and coating defects around unsealed weld areas and vent holes.  Similar to stains caused by weeping.  See Surface Condition 26

Cause

Pre-treatment chemicals penetrating sealed overlap areas through the required vent holes and escaping during immersion in the molten zinc.  This effect tends to damage the flux coatings, causing localised uncoated areas.

Effect / Remedy / Responsibility

This can be accepted once repaired after cleaning. 

The Designer and fabricator should take this into account during the design and manufacturing phase of the project.

×

6. CLOGGED HOLES

6. CLOGGED HOLES

What is this?

Zinc film clogging or partly bridging holes.

Cause

Molten zinc has a high surface tension and will not easily drain from holes under 8mm in diameter.

Effect / Remedy / Responsibility

This can be accepted once the item has been cleaned if required.

The Designer should make the holes as large as possible.

The removal of molten zinc over the bath by the galvanizer will reduce the likelihood of clogging.

×

7. CLOGGED THREADS

7. CLOGGED THREADS

What is this?

Threaded components or attachments have threads clogged with zinc.

Cause

Insufficient centrifuging or poor drainage of threaded attachments on withdrawal from the galvanizing bath.

Effect / Remedy / Responsibility

This should be rejected and then cleaned by the galvanizer.  The correct centrifuging equipment or post galvanizing thread cleaning by heating and wire brushing or oversize tapping of nuts, will generally remove clogging.

If necessary, specify delivery of bolts and nuts in nutted up form.

×

8. DAMAGED COATINGS CAUSED BY WELDING OR NON-CONVENTIONAL FIXING METHODS DURING ERECTION

8. DAMAGED COATINGS CAUSED BY WELDING OR NON-CONVENTIONAL FIXING METHODS DURING ERECTION

Cause

Conventional drilling and bolting after hot dip galvanizing is preferred.  Should welding or a non-conventional method of fixing be used, which results in damage to the coating, an approved repair method is necessary.

Effect / Remedy / Responsibility

Coating repair can be done by zinc metal spraying or a zinc rich paint or epoxy, providing the product conforms to the requirements of the specification.

×

9. DISCOLOURATION AFTER HOT DIP GALVANIZING CAUSED BY GRINDING OR OTHER RESIDUES

9. DISCOLOURATION AFTER HOT DIP GALVANIZING CAUSED BY GRINDING OR OTHER RESIDUES

Cause

Material stored in contact with rusty steel or iron filings, can cause surface rust staining.

Effect / Remedy / Responsibility

This can be accepted as once the cause has been removed the stains will gradually disappear.  The Fabricator should clean if possible.

×

10. DISTORTION

10. DISTORTION

What is this?

Distortion is the unwanted warping that occasionally becomes evident after hot dip galvanizing.

Cause

The hot dip galvanizing process occurs at a molten zinc temperature of 450°C.  This is at the lower end of the stress relieving temperature for treating steel.  Thus, any inherent rolling or welding stresses in the fabrication are likely to be released.  This may result in a dimensional change, i.e. distortion.

Effect / Remedy / Responsibility

The Designer has the following options available:  use symmetrical designs; use sections of similar thickness; stiffen unsupported thin wall sections; use preformed members with the correct minimum bend radii; use balanced or staggered welding techniques; make use of temporary braces on thin walled sections such as troughs, cylinders and angle frames.

Stress Relief assembly prior to hot dip galvanizing.

The galvanizer should avoid quenching after galvanizing.

The components can be straightened after hot dip galvanizing.

×

11. DRAINAGE SPIKES

11. DRAINAGE SPIKES

What is this?

Spikes and teardrops of zinc often appear along the edge of a component after hot dip galvanizing.

Cause

The edge most likely to have these spikes is the last to leave the bath on withdrawal.  This applies particularly to complex fabrications.

Effect / Remedy / Responsibility

Drainage spikes are easily removed at the bath while still molten but any solidified spikes should be removed by careful fettling by the galvanizer prior to release.

×

12. DULL GREY OR MOTTLED COATING APPEARANCE

12. DULL GREY OR MOTTLED COATING APPEARANCE

What is this?

Dull grey or mottled coatings can appear as a dark grey circular pattern, a localised dull path, or may extend over the entire surface of the component.

Cause

This appearance indicates the presence of extensive iron / zinc alloy phase growth, caused by steels with high reactive levels of Silicon and Phosphorus.

Effect / Remedy / Responsibility

Although not as aesthetically pleasing, a dull grey coating provides similar or better corrosion protection. 

×

13. ENTRAPMENT OF ASH

13. ENTRAPMENT OF ASH

What is this?

Ash which has not been removed from the surface of the molten zinc prior to immersion of steel can be trapped on the steel surface as it is immersed and result in an uncoated surface beneath the trapped ash.

Cause

Inadequate skimming of ash from the molten zinc surface prior to dipping.

Effect / Remedy / Responsibility

On removal of entrapped ash, small uncoated surfaces shall be repaired according to the requirements of SANS 121: 2011 (ISO 1461:2009) by the Galvanizer.

Large defects greater than 0.5% of total surface area or single spots over 10cm2 are a cause for rejection and require stripping and re-galvanizing.

×

14. FLAKING OR DELAMINATION OF COATING

14. FLAKING OR DELAMINATION OF COATING

What is this?

No adhesion of zinc to the steel surface or a thick, rough coating.

Cause

High phosphorus content greater than 0.02% can cause the entire coating to delaminate from the steel.

Effect / Remedy / Responsibility

The Designer should use a steel that has a phosphorus content of lower than 0.02%.

×

15. FLUX DEPOSITS, STAINS AND INCLUSIONS

15. FLUX DEPOSITS, STAINS AND INCLUSIONS

What is this?

Flux deposits or stains from the galvanizing process may adhere to the steel or become included in the coating.  Flux residues are black, brown, grey or yellowish non-metallic deposits consisting mainly of ammonium chloride.

Cause

Flux deposits or stains may occur as a result of excessive (dusting) with ammonium chloride on withdrawal from the molten zinc.  Flux inclusions can occur when a surface flux blanket is applied to the zinc surface (wet galvanizing).  Flux blankets are normally only used for specialised processes, e.g. galvanizing tubes and fasteners.

Effect / Remedy / Responsibility

Flux deposits or stains should be removed by the galvanizer and the underlying coating measured to determine whether it conforms to the minimum requirements of the specification.

×

16. DISCOLOURATION OF THE PAINT COATING OVER HOT DIP GALVANIZING AFTER EXPOSURE TO THE ENVIRONMENT

16. DISCOLOURATION OF THE PAINT COATING OVER HOT DIP GALVANIZING AFTER EXPOSURE TO THE ENVIRONMENT

Cause

Inadequate repair of a damaged surface on the hot dip galvanized coating prior to the application of a paint coating.

Effect / Remedy / Responsibility

It is the installers responsibility to ensure the correct repair materials and application procedures are used when touching up cut or welded hot dip galvanized components and prior to painting.  Where corrosion control has been compromised the job should be rejected.

×

17. MECHANICAL DAMAGE

17. MECHANICAL DAMAGE

What is this?

Mechanical handling or transport damage can occur, particularly with extremely thick coatings.

Cause

The use of chains, wire ropes, dragging or dropping of the component onto a hard surface, can cause mechanical damage.  This is particularly relevant with thick coatings.

Effect / Remedy / Responsibility

This can be accepted and repaired by the galvanizer or builder if necessary.

Warning labels highlighting possible damage if manhandled, should be attached by the galvanizer before the component is transported.  The use of nylon lifting slings is recommended.

×

18. OXIDE LINES

18. OXIDE LINES

What is this?

Light aluminium oxide film lines on a hot dip galvanized surface.

Cause

Due to the shape and / or drainage conditions of some components, the hoist crane has stopped and started upon withdrawal of the items from the molten zinc.

Effect / Remedy / Responsibility

This can be accepted as it has no effect on corrosion resistance, with the overall appearance becoming uniform in time.

×

19. PIMPLES OR BLISTERS

19. PIMPLES OR BLISTERS

What is this?

Pimples or blisters formed during hot dip galvanizing are usually associated with surface imperfections such as dross inclusions.

Cause

Dross pimples result from agitation of the dross layer at the bottom of the bath or from dragging material through the dross layer.  They appear as small, hard lumps on an otherwise normal galvanized surface.  Blisters may be formed by hydrogen, which is absorbed during pickling and diffused at galvanizing temperatures.

Effect / Remedy / Responsibility

This can be accepted since dross pimples represent minor disturbances in coating uniformity and do not affect corrosion resistance.  Smooth if sufficiently sharp to create the risk of injury.

The galvanizer should avoid disturbing the dross layer at the bottom by controlling immersion depth and drossing regularly.

×

20. REACTIVE AND NON-REACTIVE STEELS, WELDED TOGETHER

20. REACTIVE AND NON-REACTIVE STEELS, WELDED TOGETHER

What is this?

Variations in coating thicknesses can arise when reactive and non-reactive steels are welded together.  Efforts to increase coating thickness on the less reactive steel may result in an undesirably thick and brittle coating on the most reactive steel.

Cause

This difference in coating thickness is brought about by a combination of a more reactive silicon killed steel and / or high phosphorus, resulting in a thicker coating and a less reactive aluminium killed steel, resulting in a coating thickness sometimes below that required in the specification. 

Should the galvanizer be asked to regalvanize in accordance with the specification, the resultant coating thickness on the reactive steel will be excessively thick, resulting in a brittle coating more susceptible to damage.

Effect / Remedy / Responsibility

The fabricator should select the same steel for fabricating on a component.

If need be, accept a concession request by the galvanizer when the thinner coating is possibly below specification.

×

21. REMOVAL OF ZINC COATING BY EXCESSIVE CLEANING

21. REMOVAL OF ZINC COATING BY EXCESSIVE CLEANING

What is this?

Unless otherwise agreed, the galvanizer will limit cleaning of the final coating by mechanical means to that required in the specification.

Cause

Excessive cleaning of the coating by mechanical methods can result in uncoated areas.

Effect / Remedy / Responsibility

Care should be exercised by the galvanizer to avoid over cleaning.  If corrosion control has been compromised, i.e. exposed areas greater than tolerance; reject. 

Alternatively repair in accordance with standards.

×

22. ROLLING DEFECTS IN STEEL

22. ROLLING DEFECTS IN STEEL

What is this?

These defects may be broadly classified as surface discontinuities in the steel that have been elongated during rolling.

Cause

Steel may occasionally include laminations, laps, folds and non-metallic impurities, which result in slivers rolled into the metal surface.  Defects of this type are sometimes detected before or after pickling, but may only become apparent after hot dip galvanizing.

Effect / Remedy / Responsibility

This can be accepted, as minor surface defects will not adversely influence coating life. 

Surface flaws in the base material may be removed by local grinding after hot dip galvanizing followed by repair of the affected surface.

×

23. ROUGH COATINGS, CAUSED BY STEEL SURFACE CONDITIONS

23. ROUGH COATINGS, CAUSED BY STEEL SURFACE CONDITIONS

Cause

Rough surfaces, typical of coatings on corroded steel surfaces, can be hot dip galvanized satisfactorily.  The coating will however, reflect the texture of the substrate.  Other causes of rough surfaces include uneven cold working, over pickling, a high galvanizing temperature and / or extended immersion in the molten zinc.

Effect / Remedy / Responsibility

This can be accepted as the rougher surface will produce a thicker coating and result in a longer service life.

×

24. ROUGH, HEAVY COATINGS CAUSED BY A ROUCH SURFACE AND / OR THE CHEMICAL COMPOSITION OF THE STEEL – “TREE BARK EFFECT”

24. ROUGH, HEAVY COATINGS CAUSED BY A ROUCH SURFACE AND / OR THE CHEMICAL COMPOSITION OF THE STEEL – “TREE BARK EFFECT”

Cause

Hot dip galvanized components showing markedly rough surfaces.  This can include coatings that have a generally rough surface and, in some cases, groove type surface configurations, “tree bark effect” caused by variations in surface steel analysis.

Effect / Remedy / Responsibility

The thicker coating produced will provide greater corrosion protection; except when the coating tends to flake off or delaminate (see surface condition 14).

×

25. ROUGH HEAVY COATINGS CAUSED BY INSUFFICENT CENTRIFUGING

25. ROUGH HEAVY COATINGS CAUSED BY INSUFFICENT CENTRIFUGING

Cause

Efficient centrifuging will generally remove excess zinc and provide a smooth and attractive exterior.

Effect / Remedy / Responsibility

Provided the steel / casting surface is reasonably smooth, correctly centrifuged articles will provide an acceptable finish.

Should the surface not be reasonably smooth; it should be rejected. 

×

26.STAINS CAUSED BY WEEPING

26.STAINS CAUSED BY WEEPING

Cause

The salts from acid or flux that have penetrated porous welding or between contact surfaces during pickling, can weep after hot dip galvanizing and water quenching, providing a stained area.

Effect / Remedy / Responsibility

Weld seepage stains are not a cause for rejection.  The stains can be easily removed by means of bristle brushing.  Should the component be destined for a corrosive area, the crevice may be sealed after cleaning.

×

27. TIGHTHLY ADHERENT LUMPS OF ZINC ON THE INSIDE OF HEAVY WALLED STEEL PIPING

Cause

Heavy walls and thick flanges used in the manufacture of piping can act as a heat sink when immersed in molten zinc.  This effect considerably lengthens the immersion time.  Occasionally the galvanizer will remove the pipes before all the zinc has melted from the inside of the pipe.

Effect / Remedy / Responsibility

The inspector should reject this.  The galvanizer should ensure all zinc has been removed from the inside of the pipe by longer immersion times.

The item can be cleaned or repaired if acceptable to the customer.

×

28. TOUCH MARKS

28. TOUCH MARKS

What is this?

The zinc in the galvanizing bath should have free access to all component surfaces otherwise small uncoated or damaged areas can result.

Cause

Articles entering the galvanizing bath should not be in tight contact with each other.  Jigging wire should also be loosely attached to eliminate wire marks.  Where a component has been resting on jigging or dipping equipment, an uncoated area or touch mark could appear.

Effect / Remedy / Responsibility

The galvanizer should minimise contact between components and jig connections (loosen jigging wire).  Small components can be centrifuged.

These areas should be repaired if within allowable limits.

×

29. TYPICAL SPANGLED HOT DIP GALVANIZED COATING

29. TYPICAL SPANGLED HOT DIP GALVANIZED COATING

What is this?

A typical hot dip galvanized surface is shown in the example.  The surface is silver grey in colour and not necessarily, but often has, a spangled effect (zinc crystals) in a range of sizes.

Cause

Surface appearances may vary according to the chemical composition of the steel.  Cooling rate has a direct effect on the surface brightness and spangle size.  Faster cooling usually results in a brighter coating with a smaller spangle size.

Effect / Remedy / Responsibility

Not rejectable if coating thickness within allowance limits.

×

30. UNEVEN DRAINAGE

30. UNEVEN DRAINAGE

What is this?

Uneven drainage results in an uneven or lumpy area on which zinc build up has occurred.

Cause

This can occur over the entire surface or in isolated areas.  Uneven drainage also includes drips on the ends of parts, runs near holes.  A cause may be high withdrawal speed and / or the galvanizing temperature being too low.

Effect / Remedy / Responsibility

This condition does not adversely affect coating performance and is acceptable. 

However, protuberances and lumps which interfere with mating surfaces are unacceptable.

×

32. UNGALVANIZED SURFACES CAUSED BY SCALE OR SAND

32. UNGALVANIZED SURFACES CAUSED BY SCALE OR SAND

Cause

Sand on cast iron or scale on the steel surface is generally caused by the process used to form or roll the product.  A localised ungalvanized area in an otherwise continuous coating can occur if scale or sand from the moulding or rolling is not removed by acid pickling or abrasive blasting.

Effect / Remedy / Responsibility

These ungalvanized areas may occur in a linear pattern on angles, channels or other rolled products.  They can also appear on cast iron products.

Uncoated areas within the limits of 0.5% of total area or single areas of 10cm2 or less can be repaired.  Larger areas are rejectable.

×

31. UNCOATED SURFACES CAUSED BY STEEL SURFACE CONTAMINANTS OR ENTRAPPED AIR

31. UNCOATED SURFACES CAUSED BY STEEL SURFACE CONTAMINANTS OR ENTRAPPED AIR

Cause

Residues (such as oil based paint, grease, oil or labels) on the steel surface or incorrectly positioned vent holes, can result in localised ungalvanized areas in an otherwise continuous galvanized coating.  Uncoated areas often manifest themselves as black or very dark coloured spots.

Effect / Remedy / Responsibility

To avoid uncoated surfaces, ensure all paint or grease is removed prior to hot dip galvanizing.  Make use of suitable marking pens for temporary identification.  Correctly position adequately sized vent holes.

Uncoated areas within the limits of 0.5% of total area or single areas of 10cm2 or less can be repaired.  Larger areas are rejectable.

×

33. UNGALVANIZED AREA IN THE VICINITY OF A WELD

33. UNGALVANIZED AREA IN THE VICINITY OF A WELD

Cause

A localised ungalvanized area near a weld can be caused by weld slag deposit, weld porosity or weld undercut.  Oxide deposits and residues from welding are resistant to normal pickling acids and must be removed before the work is pickled and hot dip galvanized.

Effect / Remedy / Responsibility

Weld slag deposits should not be accepted prior to galvanizing and must be removed by the fabricator by means of abrasive blast cleaning.  The deposit can also be removed by proper chipping or wire brushing.

Shielded arc welding as opposed to stick welding is preferred for components which are to be hot dip galvanized.

Since corrosion control is compromised, this is rejectable; but may be repaired after negotiation.

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34. WELD SPATTER

34. WELD SPATTER

What is this?

Weld spatter is oxidised, normally spherical expelled weld metal, that is fused (or not) onto the surrounding material during welding.

Cause

Weld spatter is caused by weld pool explosions when improper welding parameters are used, or if the material is dirty or contaminated.

Effect / Remedy / Responsibility

Loosely adherent weld spatter should be removed by the fabricator prior to hot dip galvanizing.  Although not acceptable in terms of the specification, the presence of tightly adherent weld spatter after hot dip galvanizing will not affect the corrosion resistant properties of the coating.

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35. WET STORAGE STAIN OR WHITE RUST

35. WET STORAGE STAIN OR WHITE RUST

What is this?

Wet storage stain or white rust (as it is commonly called) is a white voluminous deposit that is occasionally found on the surface of a freshly galvanized coating.

Cause

Wet storage stain (zinc hydroxide) is formed on freshly galvanized surfaces which are in close contact in the presence of moisture. 

Effect / Remedy / Responsibility

Wet storage stain ceases when the cause is eliminated, i.e. the objects are separated and dried.  Once it has been removed (with a nylon bristle brush) an evaluation is possible. If the coating thickness at the affected area is equal to, or greater than the minimum required in the specification, it is not a cause for rejection.  The customer is to exercise caution during transport and storage to eliminate the susceptibility to wet storage stain.

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36. ZINC METAL SPRAYED REPAIR APPLIED TO INADEQUATELY BLASTED SURFACES OR NOT WIRE BRUSHED AFTER APPLICATION

36. ZINC METAL SPRAYED REPAIR APPLIED TO INADEQUATELY BLASTED SURFACES OR NOT WIRE BRUSHED AFTER APPLICATION

Cause

In order for zinc metal spraying to adhere on applications, the damaged galvanized surface must be adequately roughened by sweep blasting or other approved methods.  As it is difficult not to overspray, excess zinc metal spray loosely adheres to the surrounding coating.

Effect / Remedy / Responsibility

The fabricator or galvanizer must prepare the surface for repair by roughening the surface by sweep blasting or some other approved method.  Loosely applied zinc metal sprayed coating at the perimeter of the repair should be removed by wire brushing.  If not removed, there is no compromise in the corrosion resistance.

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37. ZINC SPLATTER

37. ZINC SPLATTER

What is this?

Splashes and flakes of loosely adherent zinc, caused by moisture on the steel surface when hot dip galvanizing.

Cause

When hot dip galvanizing on unusually deep fabrications by double dipping, moisture on the surface of the steel contacts with the molten zinc causing splashes of zinc to loosely adhere to the already hot dip galvanized surface.

Effect / Remedy / Responsibility

The loosely adherent zinc splashes are easily removed and should be prior to release.  An experienced galvanizer can ensure the coating overlap on double end dipped surface, is not visible.

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