Method Statement for External Protective Coating of Steel Pipes and Fitting Joints

By | December 8, 2020

This document covers works for the external coating of steel pipes and fitting joints and tests along with a recommendation of generic material types.

All the inspection will be performed in accordance with the ITP for field external coating roof steel pipe fittings and joints.

Inspections should be performed by QC inspectors who are certified by the coating material manufacturer.

Measuring devices shall be calibrated before using and calibration record to be maintained on project site.

Below is list of codes and standards that are relevant for this method of coating.

API Standard 5L Specification for Line Pipe (Latest Edition)

EN 12068:  External coatings for the corrosion protection of buried or immersed steel pipelines used in conjunction with cathodic protection.

NACE RP 0274 High voltage electrical inspection of pipeline coatings.

ISO 8501-1: Preparation of steel substrates before application of paints and related products – Visual assessment of surface cleanliness Part 1: Rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous coatings

ISO 8502-3: Preparation of steel substrates before application of paints and related products. Tests for the assessment of surface cleanliness Part 3: Assessment of dust on steel surfaces prepared for painting (pressure sensitive tape method)

ISO 8502-4: Preparation of steel substrates before application of paints and related products. Tests for the assessment of surface cleanliness. Part 4: Guidance on the estimation of the probability of condensation prior to paint application.

ISO 8502-9: Preparation of steel substrates before application of paints and related products. Tests for the assessment of surface cleanliness Part 9: Field method for the conductometric determination of water soluble salts

ISO 8503-2: Preparation of steel substrates before application of paints and related products. Surface roughness characteristics of blast cleaned steel substrates Part 2: Method for the grading of surface profile of abrasive blast cleaned steel Comparator procedure.

ISO 8503-5: Preparation of steel substrates before application of paints and related products. Surface roughness characteristics of blast cleaned steel substrates. Part 5: Replica tape method for the determination of the surface profile.

ISO 2808: Paints and varnishes – Determination of film thickness

ISO 11124: Preparation of steel substrates before application of paints and related products-Specifications for metallic blast-cleaning abrasives

Surface Preparation

Visual Inspection Prior to the Commencement of Surface Preparation

Prior to the commencement of the surface preparation for the field joint coating operations, a visual inspection shall be performed on the field joint coating area in order to verify that there are no steel defects or contamination with oil, grease, soil, dirt or other similar contaminants.

All weld spatter, weld slag, sharp edges, etc. shall be removed from the field joint coating area prior to surface preparation.

In case oil, grease, residues of some adhesive materials or similar contaminants are detected, they shall be removed using a detergent, suitable solvent as per the specification, power tool brushes or any other appropriate method which can remove the contaminant from the field joint coating area. In case soil, dirt or similar loose contaminant is detected, it shall be removed with a clean cloth or with dry and oil-free compressed air, depending on the convenience of the method.

Note: Any steel defects shall be reported to the contractor supervisor and/or repaired according to the project procedures and specifications.

Salt Contamination Test After Blast Cleaning

The salt level on the bare steel pipe surface shall be measured according to ISO 8502-9 and shall be a maximum of 20 mg/m².

Cleaning of the Field Joint Coating Area

The steel surface shall be cleaned using approved blast cleaning abrasives and shall be protected from bad weather conditions such as rain or strong winds which may introduce contaminants such as soil, sand, dirt, or other similar materials to the field joint coating area.

Prior to the commencement of blast cleaning, protective shields shall be wrapped around the outer cutback edges on either side of the joint to prevent degradation of the 3LPE mainline coating edges.

The blast cleaning abrasives shall be, at all times, kept dry, clean and free from contamination.

The blast cleaning shall be performed when the following conditions are satisfied:

  • The steel surface temperature on the field joint coating area is at least 3ºC above the dew point, which shall be checked using a digital thermometer and contact temperature probe
  • Steel surface preparation shall only take place when the relative humidity at the field joint is less than 85%
  • The steel surface on the field joint coating area shall have no traces of moisture

In the case that the steel surface temperature is less than 3ºC above the dew point or traces of moisture are detected on the steel surface, the steel surface shall be heated using propane torches until the steel surface temperature is within the range of 40ºC to 50ºC. This temperature shall be maintained until all of the moisture has been removed from the steel surface.

The exposed steel surface on the field joint coating area shall then be blast cleaned in order to achieve a steel surface cleanliness grade of Sa 2½ as per the ISO 8501-1 standard, and a surface roughness of 75 mm to 125 mm as per ISO 8502-4. In case the specified cleanliness grade or surface roughness has not been achieved, the steel surface shall be re-blasted. The protective shields/masking material shall then be removed from the field joint coating edges.

Preparation of Adjacent 3LPE Factory Coating Surfaces

3LPE factory coating shall be abraded using a grit flat abrasive disc (P24, P40, P100 , etc. or other suitable process) for a minimum width of 100 mm on either side of the field joint. The 3LPE surface shall be lightly abraded around the entire circumference of the pipe and shall be free of any contaminant which can prevent successful application of the field joint coating materials. The ends of the 3LPE factory coating will then be chamfered to a transition angle of within 15-30º.

Final Cleaning of the Field Joint Coating Area

After completion of the surface preparation, the field joint coating area shall be cleaned with a cloth or with dry and oil-free compressed air to remove any loose debris or other surface contaminants.

Inspection Of Prepared Surfaces

Visual Inspection

After cleaning, the field joint coating area shall be visually inspected for the surface cleanliness grade (minimum Sa 2½) and for any surface imperfections which may prevent successful application of the field joint coating material.

If surface imperfections are detected, those imperfections shall be rectified prior to continuing with the epoxy and heat shrink sleeve application. This remedial work shall not reduce the pipe wall thickness nor the thickness of the factory applied coating below the value specified in the relevant project documents.

Surface Roughness After Blast Cleaning

The surface roughness shall be measured after blast cleaning . The surface roughness measured after blast cleaning shall be within a surface profile range of 75 mm to 125 mm with a sharp, angular blast profile

Dust Contamination Test After Blast Cleaning

After blast cleaning is completed, the dust contamination on the bare steel pipe surface shall be measured according  to ISO 8502-3.

The resultant  dust contamination shall be of a rating Class 2 or better, as per ISO 8502-3.Method Statement for External Protective Coating of Steel Pipes and Fitting Joints

A clear strip of cellophane tape (or equivalent) shall be firmly pressed onto the bare steel surface and carefully peeled off.

The tape strip shall be immediately applied to a white piece of paper with no prior contamination.

The guidelines in the ISO 8502- 3 specification shall then be used to asses the level of dust contamination on the blasted steel surface.

Maximum Time Between Surface Preparation and HSS Application

The maximum time elapsed after completion of the abrasive blasting operation and the application of the GTS-80 heat shrink sleeve shall not exceed four hours.

At no time shall the steel surface temperature be allowed to drop below the dew point before application of the heat shrink sleeve. Should either of these conditions apply, the surface preparation shall be re-inspected and/or the surface preparation repeated as required.

If the prepared surface shows signs of contamination at any time before the heat shrink sleeve is applied, the surface preparation shall be repeated as required.

Application of Gts-80 Heat Shrink Sleeve

Visual Inspection

Immediately prior to field joint coating operations, a visual inspection shall be performed on the field joint coating area in order to confirm that there are no surface preparation defects and that there is no surface contamination by oil, grease, soil, dirt or other similar contaminants. Any remedial action required to correct surface preparation issues shall be addressed prior to field joint coating application.

Initial Joint Pre-Heat Prior to Epoxy Application

The surface temperature of the bare steel cutback shall be measured using a digital thermometer and contact temperature probe. If the temperature is found to be below 50 to 70ºC or if the temperature is less than 3ºC above the Dew Point, the bare steel cutback shall be heated using propane torches to within the specified range (and ≥3ºC above the Dew Point). The actual surface temperature of the steel shall be measured and recorded for reference.

Mixing of Liquid E Epoxy/Primer

The liquid E Epoxy/Primer shall be supplied in a bubble pack configuration with a clip separating the base and cure components  prior to mixing.  The E Epoxy/Primer shall be maintained according to manufacturer recommendations prior to mixing and shall be provided in sufficient quantity to coat the field joints to specification requirements.

E Epoxy primer base and cure will be used coming with 5 US gallons each in thin cans. Mixing ratio is 3/1 (base+ cure).

To begin the mixing of each E Epoxy/Primer bubble pack kit, the separation clip between the base and cure components shall be removed and the components shall be mixed together within the bubble pack using a roller for a minimum time period of 1 minute per pack to ensure that a uniform mixture is achieved. )

Application of E Epoxy/Primer

The E Epoxy/Primer shall be applied only onto the exposed bare steel surface area and factory applied FBE and this should also be abraded but not removed by operators wearing protective latex gloves and using the applicator pads supplied within the epoxy kit. The epoxy shall be applied by four operators (two on each side of the field joint) to achieve a minimum Dry Film Thickness DFT of 250 mm, the DFT shall be measured at each of 4 different equidistant locations (12,3,6,9 o’clock positions) on epoxy primed steel surface.

E Epoxy primer should be overlapped on to FBE and by 10mm only on to the edge of the HDPE. The Wet Film Thickness WFT targed should be 305 microns.

Force Curing of E Epoxy/Primer

Once the E Epoxy/Primer has been applied and its wet film thickness verified, the field joint coating shall be heated to within 90-100ºC, using propane torches.

The surface temperature of the field joint shall then be measured and recorded at the epoxy/steel surface at the centre of the cutback, and on the adjacent 3LPE coating.

This will ensure that adequate curing of the E Epoxy/Primer has been achieved and that sufficient heat has been supplied across the cutback and 3LPE factory coating overlap area for full bonding of the HSS adhesive during sleeve application.

Application of Adhesive Weld Bead Strip

For thickness over the weld seam, the Adhesive Weld Bead Strip shall immediately be brought over to the field joint coating area and shall be wrapped around the pipe directly centered over the weld bead. The strip shall be patted into place with a gloved hand and the pre-heat of the pipe surface shall be sufficient to hold the strip in place until the GTS-80 heat shrink sleeve is applied.

Installation of The GTS-80 Heat Shrink Sleeve

To begin the GTS-80 heat shrink sleeve installation, the release liner shall be partially removed from the adhesive side of the sleeve at the underlap end. Using a propane torch with a gentle flame intensity, the subject area shall be heated for a distance of approximately 150 mm from the end of the sleeve, across the sleeve’s full width.

The sleeve shall be positioned on the pipe, directly over the field joint area, with the underlap located at either the 10 o’clock or 2 o’clock position and the sleeve centered across the width of the field joint. The pre-heated underlap end of the sleeve shall be pressed firmly into place using a gloved hand and the remaining release liner shall be removed from the adhesive side of the sleeve.

The sleeve shall then be wrapped loosely around the pipe and the overlap end of the sleeve shall be positioned directly over the underlap end leaving the extra (loose) sleeve material positioned at the bottom of the field joint. The backing side of the underlap and the adhesive side of the overlap and closure shall be heated gently with a propane torch and then patted down with a gloved hand, moving from one side of the field joint to the other.

Additional heat from the propane torch and a J-Roller shall be used to firmly adhere the closure and overlap in place and any wrinkles shall be smoothed out using the roller to work them from the centre of the closure towards the outer edge.

Four operators (two on each side of the field joint) shall continue the installation process by heating the centre of the sleeve around its circumference using propane torches with a moderate flame intensity. The torches shall be angled towards the centre of the field joint at all times during the initial recovery phase.

As the centre of the sleeve recovers towards the pipe surface, the operators shall continue heating the sleeve from the centre towards the outer edges. Care should be taken to ensure that excessive heat does not cause the sleeve surface to smoulder during this process. Should this occur, the torch should be temporarily moved away from the subject area or the intensity of the flame should be reduced. Any minor/infrequent occurrences for < 3-5 seconds should not produce a rejected sleeve.

For repeated occurrences, additional operator instruction shall be required to improve the application technique such that the intensity of the flame is reduced and/or the flame is moved across the sleeve surface more quickly during shrinking. A final decision on the quality of the sleeve application shall be made during visual inspection once the sleeve is fully installed.

The initial recovery shall be complete when the GTS-80 sleeve fully conforms to the entire underlying joint profile. Additional post heating shall then be applied over the sleeve surface using long horizontal strokes to conclude the recovery process.

The operators shall check the sleeve adhesion using a gloved finger or probe to pull at the sleeve edges to ensure that full adhesion has been achieved.

The sleeve shall be considered well bonded to the underlying steel surface and adjacent mainline coating when the adhesive and coating remain fused and adhesive begins to flow out of the sleeve edges, all around the circumference of the joint. If necessary, additional heating shall be applied to the required areas.

While the sleeve surface is still hot and soft, the operators shall use J-Rollers as required to gently roll the sleeve surface in order to push any trapped air up and out from under the sleeve and to promote adhesion to the underlying pipe surface especially at the coating overlap areas around the circumference of the pipe on both sides of the field joint.