Abstract
Heat Shrink Sleeve (HSS) coatings technology is based on radiation cross-linking of Polyethylene and Polypropylene sheets in combination with multiple types of adhesive chemistries. Heat Shrink sleeves have been and continue being used for the corrosion protection of Oil, Gas, Water and District Heating pipelines. This paper addresses the laboratory studies of the long term thermal, oxidative and hydrolytic stability of radiation cross-linked polyolefin as used in Heat Shrink Sleeves. Studies are presented on the results of long term heat aging and predicted life expectancy based upon Arrhenius plots. Analysis such as oxidation induction time, dynamical mechanical properties, peel adhesion and physical mechanical testing are discussed as test methods to validate and predict long term stability and projected life expectancy for in-service on operating pipelines.
Introduction
High performance pipeline corrosion protection and insulation coatings have been developed to meet the demanding requirements of pipelines operating over a wide range of field conditions. Today, a variety of pipe coating technologies are commercially available and selection has evolved along geographical lines. Important factors determining the coating selection relies on the pipeline construction, pipe transportation and handling, and operating conditions. As an example, coating damage is a real concern in regions where limited transportation infrastructure, rough pipe handling, aggressive backfills and high populations are prevalent. This creates the need for robust, multi-layer coating systems.
The steel pipelines are generally coated with polymeric materials such a 3-layer PE and, 3-layer PP coating systems (consisting of an epoxy layer as corrosion barrier, tie layer as an adhesive layer and an outer mechanical layer defined as top coat), polyurethane, single layer fusion bonded epoxy, dual layer fusion bonded epoxy and multilayer insulated systems etc.
All these coatings are plant applied in stationary or portable coating plants. The coating at the end of each pipe length is cut back over a length of 150 mm ±20 mm1. These pipes are then welded together in the field leaving a portion of bare steel exposed. The bare steel needs protection from corrosion. There are several field joint coating solutions for example, injected or sprayed coatings, polyurethanes, cold applied PE tapes, welded PP materials, and heat shrinkable sleeves (HSS).
HSS have been commercially available since pipeline coatings applied in manufacturing plants became commonplace in the early 1960s.
