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3015 PREFABRICATION PRIMERS

MARINE SYSTEM

a four page issue January 2010

revision of September 2005

GENERIC TYPES

The most commonly encountered prefabrication primers are:

– Reinforced polyvinyl butyral (PVB) prefabrication primers.*

These have satisfactory application, welding and handling properties, but have a lower anticorrosive

performance, especially as part of a system for immersed areas in conjunction with cathodic protection.

– Zinc epoxy prefabrication primers.

These have good anticorrosive properties and acceptable cutting and welding properties.

– Red oxide epoxy prefabrication primers.

These have good weatherability, reasonable cutting and welding properties, but show a moderate thermal

stability and poor resistance to seawater exposure with cathodic protection.

– Zinc silicate prefabrication primers. (SigmaWeld 165) 

These have excellent heat resistance and weatherability and acceptable cutting and welding properties.

– Reduced zinc silicate prefabrication primers. (SigmaWeld 199) 

These have excellent cutting and welding properties, especially in MIG/MAG welding techniques, excellent

heat resistance and good weatherability.

WELDING 

The welding techniques generally used, are:

Manual Metal Arc welding (MMA)

Gravity welding

Submerged Arc welding (SAW)

Metal Inert Gas / Metal Active Gas welding (MIG/MAG)

It is known that automatic welding confers considerable economic advantages to construction yards and the

MIG/MAG technique in particular has become economically attractive because it can also be used on thin

plate without too much distortion.

These welding techniques are characterized by the following properties.

MMA Gravity Welding SAW MIG/MAG

Welding position all horizontal horizontal all

 Automatisation minor yes common yes

Deposition rate low high high medium

Heat distortion medium high high low

Cost indication high medium low medium

* The chromium content of these primers may be detrimental to the health of operativesand Sigma Coatings has therefore discontinued the use of these products.

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3015 PREFABRICATION PRIMERS

MARINE SYSTEM

January 2010

The ‘weldability’ of a prefabrication primer is generally described by the tendency of the primer to producelittle or no porosity in a weld.

During welding, the type of primer will influence spatter formation, especially in case of MIG/MAG welding.

Generic type MMA/gravity

Prefabrication primer all positions

MIG/MAG SAW

1G 2F 3F 1G 2F

Red oxide epoxy + ± – ± –

(P) P P (P) P

Epoxy-zinc + ± – – + –

(P) P P P

Zinc silicate + + ± – + ±

SigmaWeld 165 (S, P) S, P (P)

reduced zinc silicate + + + + + +

SigmaWeld 199

1G = Butt welding

2F = Horizontal (automatic) welding of T-joint

3F = Vertical downward welding of T-joints

P = PorosityS = Spatter

+ = Excellent

± = Possible defects, between brackets the type of defect

– = Defects

THERMAL STABILITY 

The thermal stability of a prefabrication primer depends on its composition.

Because of its inorganic nature, the behavior of silicate primers is, in this respect, excellent.

During cutting and welding, silicate primers, like SigmaWeld 199 and SigmaWeld 165,

can withstand temperatures up to 1000°C for short periods.

This high level of thermal stability has several practical advantages

– cutting and welding damage is minimized

– fumes created by hot work procedures will be reduced

– the amount of weld spatter will be reduced

– weld spatter will not adhere to the primed steel

By comparison organic prefabrication primers can only resist temperatures up to 500°C for short periods.

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3015 PREFABRICATION PRIMERS

MARINE SYSTEM

January 2010

HEALTH AND SAFETY 

Fumes are inevitably generated during welding and cutting due to combustion of primer material.

The amount and composition of such fumes depends on the raw materials from which the prefabrication

primer has been made.

Fume extracting equipment should be used in case primed steel has to be welded or cut in confined spaces.

 All Sigma Coatings’ prefabrication primers are checked by the North of England Industrial Health Service and

fulfill Occupational Exposure Limits requirements (see information sheet ‘Health certificates for

prefabrication primers’ 1881).

WEATHERABILITY 

The weatherability of a primer is a function of the quality of surface preparation, film thickness applied, type

of environment to which the plates and/or sections are stored and degree of damage to which they are

subjected during this period.

In general zinc dust primers will perform better during atmospheric exposure than primers formulated with a

minimum amount of zinc or containing no zinc at all.

Primers with a high zinc content can therefore be applied at lower dry film thicknesses.

SECONDARY SURFACE PREPARATION

In order to ensure satisfactory adhesion of the subsequently applied system, prefabrication primed sections

have to undergo some degree of secondary surface preparation prior to system application.

The degree and type of secondary surface preparation required before application of the full coating system

depends on:

the resistance to exterior exposure of the prefabrication primer

the service conditions of the subsequently applied system

the prevailing shop regulations

 At the very least, this involves removal of dirt, dust and debris; but other problems will be associated with

handling damage, weldseams, burn damage or excessively weathered plate.

Generally, weldseam areas and corroded or burned areas will require thorough blast cleaning or mechanical

cleaning. Zinc salts should be removed by sweepblasting or by abrading mechanically using silicon carbide

impregnated abrasive pads (SCAP).

 A total lack of surface preparation, an insufficient degree thereof or an inappropriate service situation can all

lead to rather serious consequences for the coating system on heat affected zones, weldseam areas and

contaminated, corroded or damaged areas.

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3015 PREFABRICATION PRIMERS

MARINE SYSTEM

January 2010

RECOATABILITY 

Beside the function to protect shot blast cleaned steel during storage and construction, a prefabrication

primer is often also the first coat of anticorrosive paint systems. Proper organization of all shop activities,

taking into consideration all specific properties of the prefabrication primer involved, will lead to the

avoidance of extensive surface preparation before overcoating.

– Epoxy prefabrication primers in sound condition may be used in coating systems which are resistant to

seawater exposure without cathodic protection.

In practice, however, these kinds of prefabrication primers are often heavily damaged by heat or

mechanical influences. This means that extra attention should be paid to the pretreatment of these

damaged areas when the steel structure has to be exposed to immersion in (sea) water. Experience

shows that blast cleaning to ISO-Sa2½ is the most effective pretreatment method for these areas and

exposure conditions.

– Zinc containing prefabrication primers may show the formation of zinc salts during weathering,

depending on exposure conditions and time. The formation of zinc salts can be avoided by overcoating

the prefabrication primer before the structure leaves the shop. If this is not possible, a second surface

preparation should take place especially after long weathering periods.

– The presence of a prefabrication primer in tankcoating systems is generally not accepted because the

chemical resistance of the tankcoating system will be diminished.

REFERENCES

SigmaWeld 165 see product data sheet 7171

SigmaWeld 199 see product data sheet 7177

Limitation of Liability - The information in this data sheet is based upon laboratory tests we believe to be accurate and isintended for guidance only. All recommendations or suggestions relating to the use of the Sigma Coatings products made by PPGProtective & Marine Coatings, whether in technical documentation, or in response to a specific enquiry, or otherwise, are basedon data which to the best of our knowledge are reliable. The products and information are designed for users having the requisiteknowledge and industrial skills and it is the end-user's responsibility to determine the suitability of the product for its intendeduse.

PPG Protective & Marine Coatings has no control over either the quality or condition of the substrate, or the many factorsaffecting the use and application of the product. PPG Protective & Marine Coatings does therefore not accept any liability arisingfrom loss, injury or damage resulting from such use or the contents of this data sheet (unless there are written agreementsstating otherwise).

The data contained herein are liable to modification as a result of practical experience and continuous product development.This data sheet replaces and annuls all previous issues and it is therefore the user’s responsibility to ensure that this sheet iscurrent prior to using the product.