Pressure Pipe Condition - Right Pipe, Right Test

Aaron Prince – Assetlife Alliance

Inspecting the condition of pressure pipes is difficult and not a lot has been undertaken in New Zealand, yet. The most critical pressure pipes are invariably difficult to access or isolate. While there are several different inspection technologies in the market there is no single method that can be used for all materials and situations, and many technologies are relatively unproven. 

It’s very tempting to utilise a single available technology or just choose pipes that are suitable for testing with that technology. It’s even more tempting to choose the pipe on Quiet Street instead of the pipe crossing State Highway 1 because it’s easier. As a result, Asset Managers are left uncertain of how to proceed to understand the remaining life of their pressure pipes and what repairs may be required before the assets fail.

One of most important tasks when planning a pressure pipe inspection is to understand what information is needed to understand the health of the pipe. The presence of air pockets? Remaining wall thickness? In sewer rising mains there may be reduced capacity so identifying sediment build up in the pipe may be required. In many cases more than one technology or method is required. For example, it may not be much use to only measure the remaining wall thickness of a pipe, because that does not tell you if the pipe is about to fail. But if you combine remaining wall thickness with monitored pressure transients and the as-built wall thickness, you can confidently understand the rate of deterioration and remaining useful life.

Once the desired information is established, the most suitable available technologies can be identified for each pipe in question. Failing to understand what information is needed, or what the limitations are, could be expensive and end up not providing useful results.

Assetlife Alliance have undertaken 60 km of successful pressure pipe condition investigations around New Zealand in the last twelve months. As a result of the recent stimulus funding, we’ve been engaged to use technologies that are new to
New Zealand. Some new technologies have experienced glitches getting up and running and we are persevering with those. Others now have a strong track record such as ePulse (non-invasive acoustic technology that assesses a pipe's average remaining wall thickness) and p-CAT (non-invasive acoustic technology that assesses a pipe’s remaining wall thickness in ten-meter increments).

This paper aims to share what has been learned from our experience of successfully completing a range of different pressure pipe projects by giving some specific project examples- from large scale highly critical asbestos cement, steel, ductile iron and plastic water mains to concrete rising mains. This paper will discuss the successes and limitations and importantly the necessary approach required to planning and scoping a pressure pipe inspection project or larger
programme in New Zealand.