The McNulty Curve

In general, mining companies have a poor track record of delivering projects on time or on budget. Today, for the first time, I heard about the McNulty Curve; a graph which predicts the level of pain that companies will endure when ramping up a project.

Some previous studies on project cost overruns highlighted a few key reasons for process plant failure (defined as major cost over-run or inability to achieve design capacity):

  1. insufficient effort was devoted to understanding process chemistry
  2. insufficient continuous pilot-scale testing was conducted
  3. the plant lacked parallel process streams and/or in-line spare equipment units
  4. the design incorporated sequential unit operations that either were first-of-a-kind or the largest ever built or both

Terry McNulty advanced this concept and derived ramp up curves for various types of processes. He defined the types as follows:

  1. Series 1
    1. The owners relied on mature technology.
    2. Standard types of equipment were selected.
    3. Thorough pilot-scale testing was done on potentially risky unit operations.
  2. Series 2 
    1. If the technology was licensed, the project was one of the first licensees.
    2. Some equipment was a prototype in size or application.
    3. Pilot-scale testing was incomplete or was conducted on non-representative samples.
    4. Process conditions were unusually severe or corrosive.
    5. Non-innovative parts of the flowsheet received inadequate attention
  3. Series 3
    1. There was very limited pilot-scale testing and important steps were ignored.
    2. Feed characteristics such as mineralogy were poorly understood.
    3. During process development, product quality received little attention.
    4. There were serious design flaws.
    5. Engineering, design, and construction were on a “fast track” with inadequate planning to offset added risk.
  4. Series 4
    1. If continuous tests were run, they were only to make the product.
    2. Equipment was downsized or design criteria were compromised to reduce cost overruns.
    3. The flowsheet was unusually complex with prototype equipment in two or more unit operations.
    4. Process chemistry was poorly understood. 

McNulty highlights a few other factors that were correlated with project over runs, some of which are particularly relevant for the mining industry.

  1. Corporate management had a promotional or overly aggressive attitude.
  2. The owners had very little day-to-day engineering input.
  3. Driving forces underlying the project were ill-conceived.
  4. The ore receiving and preparation areas received little attention.
  5. Translation of the testwork to design criteria was flawed.

Sources: Most of this information was from a paper called Minimization of Delays in Plant Startups. It can be found here: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.126.1359&rep=rep1&type=pdf#page=119

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