- 4 May 2017
- Posted by: Stm Coatech
- Category: Educational Articles
- 2LPE Layers
The product has cold flow and self-healing properties and also has good lap and shear strength properties to resist soil stress.
The top layer is a high-density polyethylene(HDPE) jacket. It may be either crosshead or side extruded. The jacket is tough and damage resistant, has good chemical resistance, a melting point of 130ºC , a brittleness temperature of -100ºC, and is UV stabilized for temporary storage.
Inspection is just like any other normal air or centrifugal blasting operation. We should now that side-extruded PE coatings have a very faint spiral line around the pipe. Take care not to confuse these coatings with tape coatings.Things to do before and following the application are:
- Check and document weather conditions
- Pre-clean(oil grease)
- Conduct pre-blast inspection for fabrication or mill scale
- Check to ensure profile matches specification
- Observe mixing of primer and its application
- Check the overlap of the side extrusion coating
- Conduct holiday test(discountinity)
- Ensure pipe is carefully handled
3. 3-Layer PE
Three-layer polyethylene coating (3LPE) looks very much like 2LPE coatings. On closer inspection, a green or red layer of fusion bonded epoxy(FBE) is visible at the cut back area at the ends of the pipe. This FBE layer is applied directly on the steel as the primer in the 3-Layer PE system.
- a.Surface Preparation
Surface preparation is the same as for 2LPE.
The layers are similar to the 2LPE,but have an added layer of epoxy,often times FBE as the base layer.
Quality control is the same as for 2LPE.
4.Fusion Bonded Epoxy
Fusion bonded epoxy (FBE) is typically green or red and looks like a “painted” finish. It may be a single layer or a two-layer “dual-powder” fusion bonded coating. A close visual inspection shows two distinct layer if it is a “dual-powder” system. The DFT of FBE ranges from 250 to 500 µm (10 to 20 mils).
The surface preparation and the coating application are a continuous in-plant process and should be followed by the steps indicated below.
Below are the steps for FBE application to incoming pipe, which is received in-shop for a mainline coating. The application process is:
=Preheat the pipe to the specified temperature(check often)
=Grit or shot blast the area to NACE2/SSPC-SP10(near white blast)
=Optional:pre-treat the area with an acid bath
=Heat the pipe to the specified temperature before applying FBE
=Apply the FBE coating(single layer FBE or dual powder). FBE is applied in powdered form by electrostatic spray
=Cure the FBE coating
=Quench the coating in a fresh water bath
=Stencil (to track anf position in line)
Inspectors must know what to look for on FBE coatings.Include these items in the inspection:
=Check pipes for mill damage(gouges,burrs,delaminations) and ensure they are ground down or repaired
=Check that all oil,grease,dirt,or other contaminants are removed
=Ensure acid bath is proper mixture (if bath required)
=Check shot/grit mix for centrifugal blasting
=Check to ensure anchor profile matches specification
=Check pre-heated oven(flame should surround the pipe completely)
=Check the temperature of the pipe before it enters the spray booth(ensure it is in the specified temperature range)
=Ensure the specified coating is applied
=Check cool down bath to ensure the speed and distance are proper for cure
=Check DFT and make necessary repairs
=Inspect for holidays using required voltage versus DFT
=Document and report all processes and observations