PR-186-214508-R01 In-Service Welding onto Ethylene Pipelines

Abstract

Welding onto an operating pipeline, or in-service welding, for modification and repair has been used safely by pipeline operating companies for many years. The two primary concerns when welding onto carbon steel pipelines are the safety of the repair crew and the integrity of the pipeline after the in-service welds have been completed. However in-service welding has been limited for some products that could react at the pipeline operating pressure if they reach a sufficient temperature that can occur during in-service welding. Even with this additional risk mitigation approach, some companies have historically been extremely cautious or have not allowed welding onto pipelines that contained some products. One such product is ethylene. Welding onto ethylene pipelines has been performed in the past but has more recently been considered a product for which in-service welding should not be undertaken due to the potential of an ethylene decomposition reaction that is exothermic and could result in a pipeline failure. The weld trials performed during this project were to test the hypothesis that an ethylene decomposition reaction that could result in a pipeline failure would not be produced as a result of in-service welding onto an ethylene pipeline. This was based on the background literature search and industry survey that showed in-service welding onto ethylene pipelines has been performed safely but generally there has been no detailed reporting of how those in-service welds were deposited. If an ethylene decomposition reaction does not result in a pipeline failure, then this work will be used to develop a relationship between welding heat inputs, pipeline wall thickness, and pipeline operating pressure under which in-service welds could safely be deposited onto an ethylene pipeline.