Dow Europe GmbH has introduced new top-coat and adhesive polyolefin materials for three-layer steel pipe coating systems. DOW HDPE 12110G, a black, high-density polyethylene (HDPE) top coat material, as well as AMPLIFY GR 320 Functional Polymer, a grafted adhesive resin, can be used to coat steel pipes. The most beneficially applicable areas are oil and gas operations, where the coatings can be used to prevent or minimise the possibility of pipeline corrosion resulting from extreme external conditions, mechanical impacts or degradation by heat or UV irradiation. In industrial trials, the new materials have met stringent performance requirements for coating large diameter steel pipes when used in a three-layer coating system with a fusion bonded epoxy (FBE). External tests have shown that different coating systems using these materials exceed the requirements of DIN 30670, prescribed by the German Institute for Standardisation, and other national standards.
As a top-coat material, DOW HDPE 12110G in a three-layer steel pipe coating system offers excellent environmental stress crack resistance (ESCR), superior physical properties and easy processing. AMPLIFY GR 320 provides excellent adhesion to both an FBE (when bonded directly onto a steel pipe) and to top-coat layers in three-layer coating systems. In addition to this, it offers easy processing, mechanical strength at high and low temperatures, good temperature resistance and low water-absorption.
Traditionally, polyethylene materials for three layer pipeline coating systems have been based on low-density polyethylene (LDPE). Some LDPEs are still used today, but over the last 10 years, the industry has moved towards medium-density polyethylene (MDPE) or high-density polyethylene (HDPE) solutions. The main reasons for the change include higher operating temperatures for pipelines and the industry’s better understanding of the crack and impact resistance needed at high and low temperatures—for example, under extreme climatic conditions. Together with indentation resistance as well as long-term thermal and UV resistance, these needs are reflected in national, international and company standards. The specific product design of DOW HDPE 12110G makes it possible to combine excellent ESCR and excellent flow behavior for exceptional processin on high-output extruders.
Polyethylene-based adhesives for steel pipe coating systems have been in focus for the last 10 years. AMPLIFY GR 320 is designed to be a high-performance adhesive that can provide excellent peel strength performance at temperatures of up to 80°C. The higher service temperature of pipelines defined the need for specific maleic anhydride grafted (MAH) formulations that were able to combine high peel strength at elevated temperatures with good processing characteristics, while exhibiting excellent long-term thermal stability. Based on oven ageing testing of AMPLIFY GR 320 at elevated temperatures of 100°C and 110°C, a minimum lifetime expectation of 50 years has been calculated and predicted for this adhesive.
AMPLIFY GR 320 and HDPE 12110G were commercialised two years ago, based on successful customer testing in different plants followed by a test of pipe samples against the requirements of DIN 30670. They are being produced in European plants operated by Dow. Certificates have been obtained from TÜV, a provider of technical, safety and certification services in Germany, for systems with different epoxy resins.
In order to demonstrate the suitability of AMPLIFY GR 320 and HDPE 12110G in three-layer steel pipe coating systems for pipelines at higher operating temperatures, a test against the EN 10288 standard was also included in the TÜV certification study. In order to test the materials in combination with different FBE materials, Dow has established a coating line in its pipe laboratory at Horgen, Switzerland. The line allows for coating 170 mm steel pipes. It has been used to optimise the processing and peel strength performance of AMPLIFY GR 320, and also to test its compatibility with the FBE materials more often used in the global steel pipe coating market. Coating system tests conducted by Dow follow all the steps that would be taken in a large-scale coating plant, including blasting, heating, powder epoxy application, adhesive application via extrusion or powder spraying, top-layer extrusion and winding, and water cooling.
As the main focus of steel pipe coating is on corrosion protection, polyolefin raw materials must contribute to the performance of the coating during the entire lifetime of the pipeline. The critical parameters are excellent adhesion and adhesion retention, durability, crack resistance and long-term stability as well as low levels of built-in stress during the coating process.
Dow has entered this market with polyolefin materials that meet and intend to exceed the current best offerings satisfying the requirements of the most demanding pipeline applications. As a first-mover in polyethylene, Dow forsees long-term growth of the steel pipe coating market in India.
The author, Olaf Henschke is Global Technical Leader for Steel Pipe Coating, The Dow Chemical Company. He can be reached at firstname.lastname@example.org Viral Shah, Senior Manager–Plastics Business, and Prajwal Shah, Senior Manager–Application Development at Dow India, can be contacted at email@example.com and firstname.lastname@example.org. respectively Co-authors