From World Pipelines, February 2019
Let’s begin with some analogies to pipeline coatings, then move to how various codes and standards view them. I will start with the basics then take a deeper look at a couple of common standards, and then give my thoughts on the performance of pipeline coatings.
Since I have a background in building construction, I like analogies that relate. The house, condo or apartment that you live in was built based on prescriptive building codes as written by the city, region, state, or country that you live in. Building departments have defined codes, licensed contractor qualification requirements and inspection procedures that ensure that dwellings are built to minimum standards. This article is intended to discuss codes that relate to pipeline construction, much like the codes that are intended to make sure that dwellings are well built.
This article also discusses standards, which, in the same analogy, would be how the concrete in the foundation, the lumber in the framing or the roofing materials are required to perform when used for construction relative to the specific building code. The testing for these materials might be qualification testing at a laboratory or in-situ testing on a site.
In the US and Canada there are regulatory bodies that look after pipeline construction. Those bodies might be state, provincial or federal agencies, depending on the scope of the pipeline. It appears to be very neat and well structured, but pipelines cross borders and international pipelines not only cross country borders but are often onshore and offshore, or transition between the two. That is not so neat and well structured, so the question is: who governs the codes and standards that relate to these pipelines? The many aspects of pipeline construction is complex, but this article will attempt to address only those that relate to coatings and, to an extent, impact of, or to, cathodic protection (CP).
The corrosion process
To start off with a basic lesson in the principles of corrosion protection design: in order for corrosion to occur, there are four required elements; an anode, a cathode, an electrolyte and an external circuit.
By removing any one of these, the corrosion process will stop. A statement made by Alan Kehr is a fundamental in the pipeline corrosion protection industry. Kehr was a leading American expert on pipeline coatings and stated that external pipe coatings are “intended to form a continuous film of electrical insulating material over the metallic surface to be protected. The function of such a coating is to isolate the metal from direct contact with the electrolyte, interposing a high electrical resistance so that electrochemical reactions cannot occur.” In this statement, Kehr advocated that the corrosion process can be stopped by removing the external circuit from the equation – essentially blocking the availability for current to flow.
Another respected expert in the field of corrosion coatings is Dr. Dennis Wong, recently retired as Technology Group Manager, ShawCor CR&D. His comment about pipeline coatings is: “The objective of a coating is to provide a barrier to the corroding species, not as some claim that their coating allows CP current to go through, which defeats the purpose of putting on a coating.” Some of the concepts and diagrams shown in this article are also attributed to him and Catherine Lam from a presentation they gave entitled ‘Compatibility of Pipeline Coatings to Cathodic Protection’, presented at the International Pipeline Coatings Technology Conference in 2017.
The basic functions of a coating are to block water, oxygen and other corrosion species, and have these attributes:
- Excellent adhesion to metal surface.
- Sufficient mechanical strength.
- Low permeability.
- High electrical resistance.
- Cathodic disbondment resistance.
- Chemically and physically stable.
There are various national and international codes and standards that make comments about coating attributes.
The US Department of Transportation Pipeline Hazardous Materials Safety Administration (PHMSA) has regulations relating to pipelines that are called the Code of Federal Regulations (CFR) 192 and 195.
- CFR 192 – Natural or other gases.
- CFR 195 – Hazardous liquids.
CFR 192 relates to gas pipelines and CFR 195 relates to liquids pipelines, and both make statements relative to corrosion protection and coatings.
CFR 192 views attributes such as good adhesion, resistance to migration of moisture, low moisture absorption and high electrical resistance as stringent requirements. Likewise, CFR 195 views adhesion, moisture resistance and electrical resistance as principal to an effective anti-corrosion coating. The interesting point is that CFR 192 has a section which states that, under certain conditions, the pipe must be protected against external corrosion by a non-shielding coating. This is contrary to the body of code but does specify that the “non-shielding coating” type is considered to be fusion bonded epoxy (FBE) and, in some cases, 100% solids, 2-component liquid epoxy (2CLE). No adhesive based or thick film coatings are mentioned.
Essentially, the requirements are:
- Be designed to mitigate corrosion of the buried or submerged pipeline.
- Have sufficient adhesion to metal surface to prevent underfilm migration of moisture.
- Be ductile to resist cracking.
- Have enough strength to resist damage due to handling and soil stress.
- Support any supplemental CP.
- Have low moisture absorption and provide high electrical resistance
In Canada, if a pipeline is contained within a province, the pipeline would fall under the jurisdiction of a provincial regulator. For example, in Alberta, these pipelines are regulated by the Energy Resources Conservation Board. If a pipeline crosses provincial or international boundaries, the pipeline is regulated by the National Energy Board (NEB) – and the majority of pipelines operated by major pipeline operating companies are regulated under the NEB. The NEB is an independent federal agency with the purpose to regulate international and interprovincial aspects of the oil, gas and electric utility industries. However, specific details relative to the construction of a pipeline tend to fall to standards as outlined by the Canadian Standards Association (CSA).
There are two well-known standards that are commonly referenced. NACE SP0169 covers coatings and CP, but really focuses on the CP side. NACE also has various standards related to coatings but they are not so comprehensive. For coatings, a set of key industry standards for plant and field applied pipeline coatings is ISO 21809 and its respective parts and, currently, NACE has established a task group to look at adopting that standard.
NACE SP0169 clearly states that coatings are the primary corrosion protective system and that CP is used as supplemental protection. Furthermore, the standard states that desirable attributes of a good coating are electrical resistance and that it will act as a moisture barrier. This is what was described earlier in the statement by Kehr.
The standard also addresses adhesion and makes the comment that unbonded coatings could shield electrical current, thus making the case that coatings with good adhesion quality should be used. By definition, shielding is caused by some external material that prevents cathodic current from getting to the steel. It is not the intent to bring highly electrically resistive coatings into this list.
In Canada, pipeline design and construction decisions are guided by a set of comprehensive standards issued by the CSA. CSA standards set out specific design criteria, including the depth at which a pipeline is buried, the thickness of pipe walls, the integrity of the welding process connecting the pipe, and the coating. CSA Z662 covers the design, construction, operation and maintenance of oil and gas pipeline systems and underground storage of petroleum products and LNG.
Within CSA Z662, Chapter 9 covers corrosion control requirements for coatings and CP. For coatings, the chapter discusses requirements for both epoxy and polyethylene type coatings.
Furthermore, CSA Z-245.20 Series, Plant Applied External Coating for Steel Pipe, covers the qualification, application, inspection, testing, handling and storage of materials required for plant-applied FBE and 2-layer and 3-layer polyethylene coatings.
There is also a field joint standard, CSA Z-245.30, which covers field applied coatings with minimum standards for testing, which are loosely based on plant applied coating standards. The interesting thing about Z-245.30, is that it really focuses on application quality and applicator training.
As excerpted from Z-245.30, it “Covers the qualification, application, inspection, testing, handling and storage of materials required for coatings applied externally to steel piping in the field or a shop.” Key words here are:
Other excerpts from CSA Z-245.30 are:
5.2 General – Qualification
Coating materials shall be:
- Qualified by the manufacturer to be in accordance with the requirements of Clause 5.3 (Qualification). The certificate of material qualification shall be available from the manufacturer upon request by the company or application company.
220.127.116.11 Certificate of applicator qualification
- Upon successful completion of the qualification testing, the application company shall provide a certificate of applicator qualification that states the following:
- The applicator’s name.
- The coating system or systems for which the applicator is qualified.
- The MQAP used to qualify the applicator.
- The date of qualification testing.
- The required evidence of qualification shall be referred to as a certificate of applicator qualification. For traceability, the certificate shall provide a unique identifier for the qualified applicator.
In reading the standards excerpts, you can see a lot of emphasis on ensuring quality application of pipeline coatings.
Internationally there are a number of pipeline coatings standards that have evolved from the likes of NACE (American), DIN (German) and EN (European), all to become a part of ISO (International) standards. The evolution has resulted in the ISO 21809 suite of standards that cover pipeline coatings (mainline and field joint). Using ISO 21809-3 as an example, this covers field joints and, amongst the ISO 21809 suite, it has the broadest coverage of coating technologies.
The standard addresses this since it contains a ‘library’ of field joint coating systems and materials and does not seek to directly contrast one system with another.
However, the standard also defines requirements for the following:
- Application procedure specifications.
- Pre-qualification trials.
- Pre-production trial.
- Inspection and testing plan.
- Quality assurance vs quality control.
The above elements ensure that a coating is properly installed. There are also common aspects between ISO and CSA.
- Performance attributes of various types or technologies.
- Qualification – of the applied systems and the applicator.
Passive and active corrosion protection
Coatings are passive systems that prevent corrosion from occurring by blocking corrosive elements from getting to the steel, like the paint on a car, and are intended to be the primary provider of corrosion protection on a pipeline.
CP systems are active systems that are designed as a back up to coatings in the case of damage or holidays. A typical passive/active system analogy is in fire protection on commercial buildings. Firewalls or fire proofing of structural members are passive systems, whereas sprinklers and fire extinguishers are active systems. The passive system is the primary protection and the active system works in conjunction. The challenge with both active and passive systems is their functionality 100% of the time. In reality, functionality largely depends on how well the systems are installed and maintained.
Functionality of pipeline corrosion protection systems is often impacted by geographic realities, which can be seen in industry trends. In the North American market, the predominant type of pipeline coating is FBE, while in many other parts of the world the predominant coating type is 3-layer polyolefin (3LPO be it polyethylene or polypropylene). There are various theories but the choice is probably a function of one or more of the following factors:
- Cost: FBE is economical and is the most ‘friendly’ to CP due to the fact that it is a thin film coating, although it is still electrically resistive.
- Availability of transportation and construction infrastructure: It is important to get the coated pipe to the right-of-way and into service without significant damage. That is easier in North America than in a Middle Eastern desert or on an offshore laybarge.
- The CP system: CP is complex and, in many situations, engineering an effective system is difficult with all the variables that must be considered. Also, in many instances, once the system is installed it may not be properly maintained.
Going back to the comment about functionality, if the transportation and construction infrastructure is good and the CP can be well engineered and maintained, then a thin film, CP friendly coating works well. In North America there is more focus on CP engineering than anywhere else in the world, so the industry tends to gravitate to lower cost coatings that will be reliant on the active CP system. Outside of North America, corrosion engineers prefer to apply focus to thick film coatings and engineer the CP as a true back up system. It is true that multi-layer thick film, high dielectric strength coatings cost more than thin film coatings, but the higher capital expenditure (CAPEX) cost is balanced by reduced construction (coating repair) costs, higher construction productivity and lower operating expenditure (OPEX) costs of maintaining a more complex CP system.
Coatings can therefore be categorised in two very basic ways: thin and thick.
How thin film coating works
- Thin film ‘thirsty’ coating.
- Dry, it is an effective insulator.
- Wet, its resistivity drops, possibly becomes semi- conductive, and may allow cathodic current to pass.
- More damage prone, which is why CP is a must.
- For dual-layer or thicker liquid epoxy systems, do they work the same way?
How thick film coating works
- Thick film barrier coating (3LPE, 3LPP).
- Wet or dry, it is an effective insulator.
- Highly damage resistant.
- Reduced reliance on CP due to toughness and high dielectric properties.
- They shield electrical current – by design.
- Cannot be overlooked because of fear of failure.
By design, 3-layer systems are thicker and insulate the substrate from the electrolyte, thus minimising future CP requirements. On a worldwide basis there have been a number of technological advancements over the last 40 years to provide better long-term performance of plant applied and field applied joint coatings. These newer coatings provide for reduced water permeability, increased electrical resistance, improved adhesion-to-steel and better mechanical protection.
The fact that pipeline failures are not in the news every day is a testament to how pipelines are built. Based on statistics gathered by both PHMSA and the Canadian Energy Pipeline Association (CEPA), pipelines have incredible safety records. Those pipelines have been protected with high dielectric strength coatings including coal tar enamel, Yellow Jacket®, 3-layer polyolefin along with FBE, with many of the field joints coated with coal tar, polyethylene tapes and heat-shrinkable sleeves.
In the introduction, a number of comments were noted relative to who governs the construction of major pipeline projects when crossing international borders, if they are onshore, offshore or a combination. Jurisdiction, especially in international waters, is complex and often relies on the pipeline owner to specify how it is built and protected. Driving quality is the shear cost of building something that an owner will want to have last a long time.
Since the reality is that pipelines are very expensive and major pipeline owners are going to build them well, from the author’s company’s experience, specifications for international pipeline construction requirements are extremely well detailed, with quality assurance and product performance well understood and documented.
All good pipeline coating systems have the potential to shield the CP system, because good coatings must be good insulators with high dielectric strength and should not allow CP current to pass (through or along a path of absorbed electrolyte). Coatings are designed to bond to the steel and, as such, shielding should not be a major consideration. However, if the path for CP current to get to the steel pipe is along the absorbed water or electrolyte path underneath the coating, then that tends to defeat the purpose of the coating.