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Why Apply Mechanical Protection?

Assets, such as offshore pipelines, risers, spools or structures, may experience impact or abrasion after they have treated the external surfaces with an anti-corrosion coating. These impact loads or abrasions may occur during transport between the anti-corrosion coating site to the assets final location or during the installation phase (lifting equipment, assembly at spoolbases or on offshore vessel) or during pipeline operations (ploughing, trenching, fishing equipment, dropped objects etc). To reduce the risk of damage to the anti-corrosion coating, a second layer of material is applied to provide mechanical protection throughout the life of the asset. This protection can avoid the cost of intervention, a high cost in offshore projects in deepwater locations.

The cycle time to apply and cure the mechanical protection coating for assets (particularly field joints onboard S lay vessels) is critical. To achieve the fastest and reliable cycle times, training of the OJS application crew, formulation of material properties (particularly curing time and impact strength) and the design of fast and reliable equipment is essential.

OJS provides four types of external mechnical protection services:

• Concrete Weight Coating (CWC) Infill Applications
   
• Three Layer Polypropylene (3LPP) Application
   
• Polypropylene Heat Shrink Sleeves (HSS PP)
   
• Flame Spray Polypropylene
   

CWC Infill Applications

CWC Infill applications normally use High Density Polyurethane Foam (HDPF).

Please click on the OJS logo on top left of this page and select OJS COATING APP labeled Sea Sleeve & HDPF to see it applied onboard an offshore pipelay vessel.

FJ 3000 - For CWC field joints requiring high density Infill, OJS offers our FJ 3000 Infill Application (see products section). Aggregate is placed within the field joint annulus and the OJS formulated elastomer FJ 3000 is injected into the mold and fills the voids between the aggregate.

Three Layer Polypropylene (3LPP) Application

OJS offers PolyFuse application equipment which applies a 1 mm thick film of polypropylene over the field joint. The field joint is coated with FBE then the film of PP is wrapped around the field joint and overlapping onto the parent coating. The PP film fully fuses with the parent PP coating. Usually 3 wraps of the PP film is applied to obtain a total of 3 mm thickness. The application cycle time is 6 minutes for 12″ dia pipe. The temperature range is minus 50 deg C to 115 deg C. OJS equipment is fully automated to ensure repeatability of the high quality field joint.

Polypropylene HSS Applications

The HSS PP application requires the steel pipe to be grit blasted to clean the steel and provide a profile to promote a bond between the steel and the epoxy layer within the HSS PP. After blasting the area is pre-heated to the manufacturers recommended temperature (approximately 80 degrees C). The HSS is then manually applied and propane gas is applied, as post heat, over the external surface of the HSS. The HSS shrinks onto the coated area and overlaps onto the parent corrosion coating and creates a watertight layer and reducing the risk of corrosion. The technicians applying this HSS PP require more training than those applying the PE HSS due to the material reaction to the post heating of the PP HSS, particularly on the overlapping area onto the parent PP coating.

Flame Spray Polypropylene

The flame spray application uses a “gun” to deposit polypropylene (PP) or polyethylene (PE) on top of the pre-coated area and builds up a consistent layer of protection similar to 3LPP or 3LPE parent coatings. The pre-coated area consists of a two layer system of 1) FBE and 2) chemically modified polypropylene (CMPP). The deposit of PP or PE by flame spray completes the 3 layer system replicating the parent coating 3LPP or 3LPE.

PP or PE powder is fed by nitrogen into a gas flame within the flame spray gun. The gun is designed to both heat the powder (without burning) and accelerate the powder onto the coated area.

Densiflex®, Sea Sleeve®, and Deep Sea Sleeve® are registered trademarks of Offshore Joint Services, Inc.