Pipe dreams – coating inaccessible pipelines

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Oil, gas and water industries are the major contributors to a worldwide network of more than 25,000 km of pipelines every year, with demand continually rising. A projected $11.63 billion will be spent on coating these lines by the year 2020. Long service lifetimes, serious safety considerations, and some of the most inhospitable areas on the planet combine to put high demands on the coatings.

Coatings represent about 10% of the total cost of new pipelines, with around 9% of the cost being taken up with factory pre-coatings and 1% with the field coatings which guarantee corrosion protection at end joints, T-joints and flanges. These field joints represent the greatest challenge: factory prepared sections are cut back to allow for welding end sections together, covering potentially vulnerable points.

Factory prepared

Factory coatings include various options depending on the purpose of the pipeline and it’s operating environment. For general underground and underwater service, and especially in highly corrosive soil environments or where perfect pipeline reliability is important, three-layer Polyethylene (3LPE) coating is generally recommended. These 3LPE coatings are intrinsically waterproof, can withstand operating temperatures of up to 80ºc and offer a long service life.

A common factory PE preparation for small and medium diameter pipes is to dry and blast the pipes to bare metal, preheat them, and then apply liquid primer or powder coating. This is followed by an adhesive tie-layer and a PE layer, extruded into a thin film from a circular die and rolled under pressure onto the pipe.

Once in the field, joints have traditionally been protected with a combination of coating technologies and spiral wrapping of tapes, and increasingly with heat-shrink sleeves.

Seal For Life Industries, part of Indiana –based Berry Plastics, are headquartered in the Netherlands. They are the biggest manufacturers and sellers of Heat Shrink Sleeves (HSS), Adhesive Pipeline Tape, and Visco-Elastic and Abrasion Resistant Overlay Ceramic epoxy.

Executive Vice President Drs. Frits Doddema explains that since, by their nature, most pipeline projects involve reaching more remote and challenging areas, the logistical problems of pipeline laying and field jointing are complex. They also require careful selection of appropriate coating technologies and materials. Special requirements for coatings can even include weight, as the weight of the coating will help to prevent an underwater gas pipeline from floating away from its supports.

“The pipes may need to be embedded in peat soils or clay, marshlands or sand, fresh groundwater or salt water. The field conditions are frequently difficult – whether too hot, too cold, too wet, too remote, or simply too cramped. Every situation is different, across underwater, underground, inshore, and offshore.“

The coating of weld girth joints in pipelines is a critical factor of the final integrity of the completed anti-corrosion system utilized. A field coating has to resist different conditions to controlled factory-grade coatings. A field coating system with higher potential failure rates can compromise the integrity of the entire system and may significantly reduce its intended design life.

Mr. Doddema continues: “Full integrity of the coatings at the joints is critical. Depending on the field coating selection, application might include steel blasting, pre-heating the pipe sections and pre-heating of the coating materials.”

“Maintenance regimes are determined by the owners but there is close oversight by regulators and owners must demonstrate good management of assets. Repairs and rehabilitation of existing pipelines brings a new set of problems.”

“Longevity requirements also vary with the purpose of the pipelines. In the 1960s requirements matched the expected lifetimes of oil and gas fields in Northern Holland, expected to be 30 years. Experience has shown that much longer lifetimes are now needed and design engineering specs are now often over 50 years and sometimes as high as 80 years.”

Repeatability

Field Jointing methods should provide equal durability, reproducibility, design life and other features to meet the requirements. Complex field jointing methods, when practical, are typically time consuming and extend the installation period, impacting total project costs in ways that are often overlooked.

“Repeatable quality in the field is key. Most traditional anticorrosion systems have developed products and special methods of application, which can provide equal system quality at field joints” says Doddema.

“Unfortunately these methods are typically complex and require special equipment and access limits that are often difficult or impossible to achieve in the field, resulting in the use of other methods that do not maintain system integrity and higher failure probability.”

“Typically the main pipe coating costs are calculated when comparing anticorrosion systems during initial specification, and field jointing costs are assumed to be insignificant because the surface area of field applications is so small in relation to the total surface area coated. This assumption is misleading as field jointing typically costs from 3-5 times more than the original parent (factory-grade) coating and in some cases far more.”

Selection of pipeline coatings has evolved along geographical lines, based on owners’ preferences, pipeline construction and operating conditions. For example, coating damage is a real concern in regions where limited transport infrastructure can lead to rough pipe handling. Other difficulties come with aggressive backfills, induced current from overhead power lines, railway crossings and heavily populated areas. These factors have created a need for robust factory coatings.

Where the pipes are being joined together, several types of external anti-corrosion and insulation field joint coatings are available. Besides the factor of compatibility with the factory coating, cutback length, type of parent coating, choice of field joint coating is affected by pipe diameter, operating temperature, construction conditions, backfill, soil conditions and contractor capabilities.

Seal For Life’s STOPAQ range of Visco-Elastic Coatings & Sealants include innovative low cost technology for rehabilitation and new construction of pipelines and field joints. The coatings are based on fully amorphous non-crosslinakable chemistry, rather than the cross-linked molecules of molten polymers. Stopaq say this avoids degradation problems encountered with conventional systems. The new material also has additional “life saving and extending” properties due to its continuous liquidlike nature, including self-healing of small damages. It is not subject to cathodic disbondment.

Tape wrapping

Denso, part of Winn & Coats, have over 85 years experience dealing with pipe coatings in a wide range of different conditions and surface preparations. The challenges fall into two main categories: Low quality surface preparation by hand power tools that will require surface tolerant coating systems, and high quality preparation by dry abrasive blast cleaning to a near white finish standard.

Their Denso Tape coating systems will tolerate low quality surface preparation, using
a variety of approaches including butyl and petrolatum tape systems. The tapes have a factory regulated minimum coating thickness and provide immediate mechanical and corrosion protection with excellent cathodic disbonding resistance. The tapes can all be applied by hand or by hand wrapping machine.

Automated Application

Another approach, the IntelliCOAT system from Canusa-CPS, takes repeatability of joint quality to another level.

The fully-automated system includes on-site computer-controlled machinery which fully encloses joint sections and applies programmed heating to pre-prepared wraps, removing most of the possibility of error by field operators. Details of each sleeve application are stored for repair and maintenance purposes.

Major lines

Across the industry business continues to look good. Current pipeline projects include a 48-inch diameter Trans Adriatic Pipeline, which will deliver 10 billion cubic metres pre annum of new Caspian gas supplies to Europe from 2020. Meanwhile Uganda will be building a 1400 km oil pipeline through Tanzania, and Indian-based Tata Steel have manufactured a large diameter 42″ pipe which will become the deepest to be laid, across 140 kilometers in the Gulf of Mexico.

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