Girthwelds, valves, fittings and fabricated assemblies

From a new construction perspective there is significant competition in the market of girthweld coatings. Out of the many possibilities there is only one system that can handle not only the coating and protection of the girthweld, but the tie-ins, valves, fittings, fabricated assemblies, namely 100 per cent solids liquid coatings. Not only can liquid coatings be used for all of the above, but they also exceed the performance characteristics of virtually all other girthweld coating systems.

Liquid girthweld material is typically sold in pre-measured containers (based on girthweld diameter) and applied with a brush and roller. This method has historically worked very well and in fact the majority of liquids sold today for the coating of girthwelds is marketed in this fashion. However, there are a few drawbacks to this packaging and application method: the packaging is some what bulky; to some extent it is time consuming to ensure an acceptable mix is achieved without air entrapment; and, while it is becoming less prevalent as experience with liquids in the field becomes greater, there is always the possibility for applicator error. One innovation created by Specialty Polymer Coatings to address this issue is the Automated Dispensing Machine (ADM). This nearly maintenance free equipment delivers a continuous supply of on ratio mixed material at the operators command. This innovation is significant, as it considerably reduces application costs, as well as providing ancillary benefits as described below. (See Figure 1).

Environmental Benefit

The ADM reduces a great deal of waste material as it saves 2 plastic containers from landfills for every girthweld (as they are non-recyclable). It also reduces material waste, as there is no longer product left on the sides of these containers.

Labour Savings

The ADM offers reduced labour requirements. Mainline coating crews typically require between four and five people, as follows: one man mixing, one man running, one man driving the truck and two men applying the material. As there is no mixing required, and the material is dispensed directly onto the pipeline the coating crew can be reduced by two labourers namely the mixer and the runner. This offers substantial cost savings over the duration of the project.

Safety Benefit

The coating is mixed on ratio (which is key for curing the material) without air being entrapped into the mixture. This reduces the amount of repairs required after holiday testing. The most common occurrence for holidays outside of insects is air entrapment in the coating.

Other Cost Saving Benefits

The material is available on an as-required basis if you need 1.25 litres (you dispense 1.25 litres, as opposed to mixing up 2 x 1 litre kits.)

Pipeline Rehabilitation

According to a study released by the National Association of Corrosion Engineers (NACE) in 2000, of the 2.2 million miles of pipeline in the USA 24 per cent was more than 50 years old and had an original design life of only 30 years. NACE further stated, “the average annual corrosion related cost of monitoring, replacing and maintaining these pipelines is estimated to be $US7 billion. The corrosion related cost of operation and maintenance constituted 80 per cent of this cost.”

A number of factors affect the longevity of a pipeline. These include quality of construction and protective coating systems utilised, cathodic protection systems employed, the nature of the external environment, the operating conditions and quality and frequency of pipeline maintenance to name but a few. No one factor influences the long-term integrity of a pipeline more than the effectiveness of its coating system. Pipeline leaks, ruptures and ultimately a pipeline’s integrity and useful life can be directly attributed to coating deterioration and/or cathodic protection failure.

SP-2888® R.G. has been used in a myriad of rehabilitation projects ranging in size from 1 - 100 metre integrity dig sections to large-scale (greater than 30 km) automated rehabilitation projects and virtually everything in between.

Horizontal Directional Drilling

Protecting directional drill pipe against gouging damage requires a barrier coating with sufficient mechanical resistance applied at sufficient thickness to withstand the dynamic forces in play pushing or pulling pipe weighing up to 400 kilograms per metre (based on pipeline diameter and wall thickness) through a pre-drilled hole in the ground subject to point loads from protruding rocks. Some damage to polymer coatings is inevitable in rigorous soils. In addition to mechanical strength, the selected protective coating must have sufficient adhesion, electrical resistance and low enough permeability to withstand buried pipeline service after being subjected to partial damage. Gouging damage must not penetrate to the steel surface. Two coating systems are generally employed in North America for HDD service. They are either a composite system or a double coat of FBE (“Dual Powder”). The Dual Powder FBE system consists of two fusion bond applications, the first application known as the primary coat is typically applied at a thickness of 10 – 14 mils (250 – 350 microns) this typically depends on the powder manufacturer. The second powder application, known as the topcoat, is typically applied anywhere from 8 mils up to 28 mils (200 – 700 microns). This depends not only on the powder manufacturer, but the severity of service the coating must withstand. These two powder combinations are applied sequentially in a coating mill for a total DFT ranging from 18 – 42 mils (450 - 1050 microns). The composite system consists of 15 mils (375 microns) dry film thickness (DFT) of FBE as the primary corrosion coating over-coated with 25 mils (625 microns) DFT of 100 per cent solids liquid epoxy as the abrasion coating for a total of 40 mils (1,000 microns). The liquid epoxy can be either applied in-line or on pipe rotators in a coating mill or at a later date in the field. The Dual Powder system performs well in light to medium aggressive soils, but lacks the mechanical strength to withstand highly aggressive environments. The composite system is frequently used in aggressive soils limiting gouge penetration to within the top protective coating film.

SP-2888® R.G. has proven to be consistently the best performer of the 100 per cent solids liquid epoxy abrasion coatings with the best application characteristics. The coating system is available in spray and brush grade formulations facilitating both plant or field application of HDD pipe with a comparable field applied girth weld coating system. In addition, SP-2888® R.G. has excellent corrosion protection properties and can be applied in a single coat application of 40 mils (1,000 microns) directly to properly prepared pipe with equal results to the composite system. The gouge resistance of SP-2888® R.G. vs. competitive systems is shown in Table 1.0. The field performance of SP-2888® R.G. applied in combination with dual powder is presented in Figures 3.0 – 3.1. Figures 4.0 – 4.2 depict horizontal directional drill process.

Three layer system

Bonding to polyolefin coatings has always presented a problem for epoxy coatings. The most popular systems for coating girth welds in Europe on polyethylene three layer coating systems has historically been various shrink sleeve systems and more recently, high build 100 per cent solids polyurethane and tar-urethane coatings. Sleeves have traditionally proved to be an application challenge on large diameter pipe resulting in poor long-term performance. Hybrid polyurethane coatings have application advantages and provide adequate flexibility to tie into three layer mainline coating systems, but only achieve tensile adhesion levels to grit blasted high-density polyethylene averaging 600 PSI (4.14 MPa). Further, they are limited by operating temperature considerations.

SPC successfully introduced a method for coating the girth welds on three layer polyethylene coated pipelines in 2002 using SP-2888® R.G. high-build epoxy. SPC’s system requires the same surface preparation as the traditional methods of coating three layer girth welds, but can be either hand or spray applied to dry film thicknesses up to 50 mils (1,250 microns). A specific pre-heating and post-heating regime is required to adequately cure the coating through winter conditions in northern climates. Once cured, SP-2888®R.G. provides more than adequate flexibility to withstand thermal stresses from sub-zero winter temperature cycles or mechanical stresses introduced when lowering in the pipe string.

The advantages of using the SP-2888® R.G. girth weld coating system on three layer coated pipelines are as follows:

  • Speed of application.
  • More ratio tolerant than polyurethane or tar urethane based systems.
  • Superior cathodic disbonding properties to polyurethane or tar urethane.
  • Excellent performance properties up to operating temperatures of 80°C.
  • Will not shield cathodic current.
  • Tensile adhesion values to high-density polyethylene averaging 900 PSI (6.20 MPa) using an ASTM D4541 TYPE 1V instrument: 50 per cent increase over polyurethane or tar urethane weld coating systems.
  • Hot water soak adhesion rating of No. 1 tested in accordance CSA Z245.20-98 (modified to 28 days immersion at 95°C).

SPC is in the process of developing an oxidation and priming system that will allow to SP-2888® R.G. to be applied to high-density polyethylene without the requirement for grit blasting. Laboratory results have produced tensile adhesion results in excess of 1500 PSI (10.34 MPa).

Conclusions

Coatings today are the primary means of corrosion protection for all buried pipelines whether it is for new construction or for pipeline rehabilitation. Although cathodic protection is applied, it is considered the second line of defence against corrosion.

100 per cent solids liquid coatings offer considerable versatility over other types of girthweld protection systems. They are the only system that provides for the coating of not only the girthwelds, but also the in situ coating of tie-ins, valves, fittings, fabricated assemblies, mainline coating, mainline coating repair, pipeline rehabilitation of varying degrees, induction bends, horizontal directional drills (in situ and mill applied). In the case of SP-2888® R.G. the coating is capable of withstanding up to 3.0 joules of impact and can be applied direct to properly prepared steel surfaces, fibreglass reinforced plastic, fusion bonded epoxy, and high-density polyethylene surfaces. It is truly a coating for use over every aspect of pipeline, and virtually all surfaces providing one single uniform pipeline coating.