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Tuesday, September 16, 2014

Weld Joint Coating on Pipelines Coated with FBE

Technical Comparison between FBE Powder and Heat Shrink Sleeves

1 - Introduction
     Both joint coatings are used in the field and both have their advantages and disadvantages with regard to materials and application methods.
1.1 - Weld joint coating with epoxy powder
     The application process is the following:
     a) clean the exposed steel by sand or grit blasting to a degree of cleanliness of SA3 (or better)
     b) provide, by the same operation and the selection of the abrasive, a surface roughness of 80 to 160 microns (as required by the epoxy powder supplier) in order to create an adequate anchor pattern for the epoxy layer to adhere to the steel surface. 
     c) eliminate all sharp edges with a file or mechanic tool (all thin film coatings need this special care as part of the surface preparation).
     d) clean both edges of the adjacent line coating with a  solvent, to remove all traces of dirt, debris, oil, grease or other contamination.
     e) preheat the joint, with due consideration to the ambient temperature and the thermal inertia of the steel mass, up to 220C, to obtain a perfect fusion of the epoxy powder particles amongst themselves and with the steel surface. 
     f) apply the epoxy powder with an electrostatic spray gun (or flocker)
     g) allow to cure
     h) check the result
     i) paint holidays in the joint coating with liquid epoxy or FBE repair sticks
1.2 - Heat shrinkable sleeves
     The application is the following:
     a) clean the exposed steel by wire brushing to a cleanliness of ST3 or alternatively SA2 or SA 2 1/2 (some products require more surface preparation than others).
     b) clean superficially the two edges of the line coating.
     c) preheate the joint area to 80-160C (depending on the manufacturer's recommendation)
     d) if applicable, precoat the bare metal and adjacent FBE with epoxy primer
     e) wrap sleeve and secure closure
     f) shrink the sleeve on the pipe
     g) inspect

2 - Comparison
     Both processes give excellent results, provided they are applied in accordance with all applicable instructions.  However, all site operations made to date with the epoxy powder spraying method have shown a major drawback:  the process is complicated and not really appropriate for some field conditions. 

2.1 - Methods
     Fusion bonded epoxy powder needs to be applied under specific conditions and using specialized equipment that can only be properly controlled in a plant and at a very complex technical level.  It is not at all easy to ensure this same performance level under field conditions.

2.2 - Equipment

2.2.1 - The equipment required for the fusion bonded epoxy powder joint coating is comprised of the following:
     - a refrigerated storage container (the shelf and storage life of the epoxy powder decreases rapidly at temperatures exceeding 20C)
     - a mobile grit / sand blasting unit, that can achieve the required anchor pattern.
     - a solvent storage outfit with fire extinguishers
     - a screening, recycling and conditioning installation (fluidized bed) plus a primary electric power source.
     - an induction pipe preheating system, including a special generator set (single phase, 800 or more cycles, special cables and an induction coil per pipe size.
     - powder spray equipment with electrostatic spray gun
     - control equipment for constant monitoring of temperature and gelling
Most of the above equipment utilizes electronic components that suffer from voltage variations, temperature excursions and vibration (coming from the generator sets on the same frame). 

2.2.2 - The equipment required for heat shrink sleeve installation is:
     - electric or pneumatic wire brushes, or a simple sandblasting outfit
     - propane torches with propane bottles, or a simple induction heating system

2.3 - Skill of operators
     The complex application procedure of fusion bonded epoxy powder requires highly qualified technicians for both, powder application and equipment maintenance.  The application of heat shrink sleeves is a matter of a few hours of training. 

2.4 - Necessary manpower
     All the various activities involved with the storage / feeding / reconditioning and application of the epoxy powder obviously require much more manpower than the simple shrinking of sleeves.  Even when labor is inexpensive, this may become an important issue.  Very often, sites are in remote locations and only limited space is available in the living quarters. 

2.5 - Ease of creating supplementary crews
     If, during the construction period, more application crews become necessary, it is very easy to put together another crew of skilled heat shrink installers, as there is virtually no supplementary equipment needed.  On the other hand, every supplementary crew for epoxy powder needs new highly skilled specialists and a complete set of the equipment described in 2.2

2.6 - Life time of raw materials
     Epoxy powder has a limited life time, depending very much on storage and handling conditions.  A heat shrink sleeve can be kept in store for an unlimited period of time and at temperatures up to 55C

2.7 - Preheating temperatures
     The preheating temperatures for epoxy powder are in the range of 220C.  To obtain a uniform thickness, a uniform preheating temperature is an absolute must.
     Preheating temperatures for heat shrink sleeves are in the range of 80-160C, depending on the adhesives used.  In case of a liquid epoxy first layer, the preheating needs only to be at 60C for all adhesives.  Preheat temperatures up to 100C can be easily achieved with propane torches under all field conditions.

2.8 - Tie-ins
     For the epoxy powder, every tie-in crew also needs a complete set of equipment.  The equipment for tie-ins needs to be even more mobile than the standard joint-protection set. 

2.9 - Back-up equipment
     For the epoxy powder process at least one complete spare set of equipment needs to be kept on hand to avoid risking the complete shut down of the job. 

Monday, September 15, 2014

Pipeline Coating Overview

Pipeline Coating Overview

     Looking through some old files, I ran across some notes taken at a pipeline coating / corrosion course not too long ago.  This course was taught by one of the leading experts in pipeline corrosion prevention in recent years. 
     Corrosion is simply the loss of chemical and/or physical integrity of the pipeline.  Corrosion is caused by four things: 
1) Primary chemical reactants (water and oxygen).
2) Secondary chemical reactants (including biological)
3) Physical damage, either before or during service
4) Electrical anomalies
     There are 10 properties required of all pipeline coatings (or: the 10 qualities of good pipeline coating).
1) Must have good adhesion to steel
2) Must be an effective barrier to water
3) Must be chemically stable
4) Must be resistant to mechanical damage
5) Must have long term physical stability
6) Must be amenable to field repair of joints and holidays
7) Must be a good dielectric
8) Must be available and cost effective
9) Must be environmentally benign
10) Must be accepted by the pipeline industry
     Next we went through generic names of different pipeline coatings along with an explanation of what they are.
1. Bituminous Enamels - Coal tars or asphalts reinforced with glass fibers and covered with an outer wrap.
2. Bituminous Mastic - a thick mixture of asphalt, aggregate, and glass fibers.
3. Extruded Polyethylene - two or three layer coatings of PE over butyl rubber, epoxy or bituminous materials.
4. Fusion Bonded Epoxy or Thin Film Epoxy - Epoxy applied as a powder to a heated pipe.
5. Liquid Epoxy - epoxy applied as a liquid; pipe is often heated before or after application in order to speed curing.
6. Extruded Rubber - premixed rubber extruded on pipe and cured in a steam heated autoclave.
7. Liquid Urethane - urethane applied as a liquid to a heated pipe.
8. Tapes - pressure sensitive, cold applied or hot applied laminates of various thermoplastic polymers.
9. Heat shrinkable plant applied - generally a spirally wrapped two layer heat shrink system which is plant applied and offers excellent high temperature corrosion prevention.
10. Viscoelastic - applied using a PE or heat shrinkable outer wrap.
     Important factors in pipeline coating applications:
1) Substrate must be clean with an adequate anchor pattern
2) Coating material must be properly mixed or otherwise uniform in consistency
3) Coating materials must be applied at the proper temperature and at the proper speed
4) Substrate must be at the proper temperature and the materials applied at the proper thickness
5) Materials must be properly quenched or cooled to the ambient temperature
6) Coating must not have any holidays or otherwise any other non-conformities
7) Coating must have adequate adhesion with no delaminations
     Commonly used pipe coating tests:
These tests are used to qualify new materials as well as to determine application quality:
1) Resistance to impact
2) Resistance to bend
3) Resistance to cathodic disbondment
4) Adhesion (peel test, etc)
5) Resistance to shear
6) Presence of holidays
7) Resistance to hot water permeation (where appropriate)
8) Thermal characteristics (where appropriate)
9) Material uniformity (where appropriate)
10) Thickness
      Pipeline coating application guideline:
1) Carry out a rigorous, though realistic, inspection program.
2) Make sure your pipeline inspectors are knowledgeable. 
3) Make sure application is strictly according to specifications.
4) If specification variation is necessary, make sure all interests are protected.
5) Do not accept job until satisfactory.
6) Maintain records on materials, application and performance.
7) Don't let application get you in a time bind.  Provide ample time for contingencies.


Wednesday, September 10, 2014

Heat Shrink Sleeve Construction Advantages

Pipeline Shrink Sleeves Construction Advantages and Benefits

     Heat shrinkable sleeves for coating pipelines (particularly- Covalence shrink sleeves which were formerly known as Raychem shrink sleeves) have a variety of advantages over other competing pipeline coating technologies. 

     Reasons to use shrink sleeves on your Onshore Pipeline:

  1. Shrink sleeves offer a fast and easy installation
    1. No special tools
    2. No special cleaning
    3. No priming (unless you choose to)
    4. Minimum labor required
  2. Covalence shrink sleeves offer a clear, positive visual inspection tool built in
    1. Shrink sleeves conform to the weld and the coating transition
    2. Heat shrink shows mastic exidation the sleeve edge
  3. Shrink sleeves are resistant to damage
    1. caused by backfill
    2. caused by pipe handling
    3. caused by skids
  4. The shrink sleeves you're using for the field joints can also be used for repairing damage to:
    1. epoxy
    2. coal tar
    3. enamel
    4. PE
    5. and other pipeline coatings
  5. Shrink sleeves can be used for coating bends (particularly our Flexclad product)
  6. Sleeves are readily available and able to ship same day from our warehouse in Conroe, TX 77385
  7. Field service and job kick off training can often be scheduled for larger jobs.  For smaller jobs, unlimited video and verbal training can be arranged.