Steven Folkman, Ron Bishop
Papers # 2016 Berlin
There are guidelines in AWWA standards for de-rating a PVC pipe’s pressure class if the operating temperature exceeds 23°C. These de-rating factors are appropriate for a system operated at a constant elevated temperature. In the warm desert climates in the USA it is common for the water mains to exceed room temperatures during summer months. However, those excursions above room temperature only last over a portion of the summer and procedures for selecting an appropriate de-rating factor are not available. It is common practice for designers to specify de-ratings based on the maximum expected pipe temperature. This approach is acceptable but overly conservative. This paper examines reported pipe temperatures and shows that seasonally the pipes undergo temperature variations that are very close to sinusoidal in nature. This paper integrates a sinusoidal seasonal variation in temperature to derive an average de-rating factor. It is recommended that these average de-rating factors be verified experimentally before being put into practice. Thus, a more conservative “effective” de-rating factor is derived. These effective de-rating factors are close to those specified in ISO 1452-2 and thus are reasonable intermediate step to use until testing can demonstrate the accuracy of the average de-rate factors derived in this paper.