Pigging Q&A part three: T.D. Williamson

We asked. They answered. Pigging experts from T.D. Williamson discuss intelligent pigs and best practice.

By Chuck Harris, T.D. Williamson Inc, USA

Q

Are ‘unpiggable pipelines’ a thing of the past?

A

The term ‘unpiggable’ is a thing of the past, the more appropriate term is ‘difficult to pig’. There are various reasons a pipeline may be deemed difficult to pig; such as trap dimensions, bend configuration, low/high pressure/flow etc. Inline inspection (ILI) service providers offer various solutions to tackle difficult to pig pipelines, and more emphasis is being placed in this area to allow pipeline operators to assess the integrity of such assets with ILI. T.D. Williamson (TDW) recently inspected two 6 in. gas gathering pipelines with a maximum pressure of 150 psi. A uniquely dressed 6 in. multiple dataset solution was employed.

In compressible products such as natural gas, components coming in contact with a large surface area of the internal diameter (ID), like urethane drive cups and brushes used to transfer magnetism, create significant drag. This drag can negatively impact tool performance, i.e., resulting in speed excursions outside optimal velocity ranges. These excursions can be greatly exaggerated in low pressure/flow natural gas pipelines. The unique solution designed by TDW reduces tool drag 3X over standard deformation and MFL configurations, and results in successfully inspecting these segments, believed to be a first in the industry in such diameter and flow.

Multiple dataset platform.

Q

How important is it for pipeline engineers to know about pressure and MAOP? How does pressure affect the inspection work you carry out?

A

It is important for pipeline operators to understand MAOP and operating pressure. ILI service providers require such information to plan for inspections. Understanding pressure is critical to tool configuration, and ultimately performance. Without taking pressure into account during the tool preparation phase, significant speed excursions could occur, resulting in data that is of reduced resolution. This impact can occur in lower pressure natural gas pipelines as a result of an elastic column of natural gas, as well as high pressure natural gas pipelines depending on flowrates. Solutions for each of the examples are quite different, where low drag may be considered for low pressure and speed control may be required for high pressure lines. Understanding expected pressures during the inspection greatly impacts run success.

Pressures are also used during the data analysis process. Typically pipeline operators require pressure calculations for each metal loss anomaly reported, using such methods as ASME B31G, Modified B31G, RSTRENG, RPR, etc. In order to provide precise safe pressure calculations for each anomaly, accurate pressures are required from the pipeline operator.

The full version of this article is published in the February issue of World Pipelines. To see this article in full, including responses to the questions listed below, click here to subscribe and receive a downloadable PDF of the February issue.

Q

How does your company use ILI datasets?

Q

Which codes and practises are crucial towards gaining a better understanding of pipeline integrity?

Edited from an article published in the February 2014 issue of World Pipelines by Elizabeth Corner

Read the article online at: https://www.worldpipelines.com/business-news/20022014/pigging_qanda_part_three_tdw/