Who I Am & the Website Connected to Dr. Leeds Co-Developer of the DCVG Technique

I have served on many NACE International pipeline corrosion control technical committees in the past, I was a pipeline industry representative on a GRI (Gas Research Institute) technical committee, I am a registered Corrosion Engineer in California, and I have worked for NGPL (Natural Gas Pipeline Company of America), Chevron Pipeline Company, Northern Natural Gas Pipeline, and BP (British Petoleum) Dome Pipeline as a pipeline corrosion engineer / integrity engineer / corrosion specialist. I have even appeared before FERC (Federal Energy Regulatory Commission) in Washington DC as a pipeline corrosion control expert witness. Therefore, I am at least experienced enough to have an opinion on this subject and I the right to defend my opinion. I even wrote the first corrosion control section draft for the very first API (American Petroleum Institute) pipeline integrity recommened practice. I give this information not to brag but to simply give sufficient background to indicate that I should know something about this subject.

The website connected to Dr. Leeds the co-developer of the DCVG technique for finding and sizing buried pipeline coating defects is located at this link. I have been trained personally by Dr. Leeds in how to do DCVG field surveys. I still have the course manual given for this training in my technical library.

http://www.dcvg.com/page28.html

I will be posting more on my blog on DCVG and other pipeline integrity methods as I have time in my busy schedule to do so.

CIS & DCVG Field Crews have to be Well Trained or the Field Data is Worthless

Wikipedia also states:

In theory, a standard analogue electronic multimeter could be used to perform a DCVG survey, but in practice it would be very difficult to take accurate readings and assess the direction of the voltage gradients correctly. A digital multimeter is completely unsuitable because of the difficulty in quickly assesing the direction of the voltage gradient. Specially designed DCVG meters are available, which have bespoke voltage ranges, specially designed transient response, rugged cases and (usually) a centre-zero meter movement for ease of use. The NACE method requires the measurements to be made using a pair of copper-copper(II) sulfate electrodes rather than simple metallic probes. In addition, the Cathodic protection is switched on and off repeatedly using an electronic switch commonly referred to as an "interrupter". Thus, two voltage readings (the "on" and "off" potentials) are taken at each fault position. Counter-intuitively, it is actually the "off" potential (measured with respect to remote earth) which is regarded as more indicative of the effectiveness of the CP applied to the pipeline. Standard surveyor's kits of DCVG equipment are available, together with training courses and software to organise and interpret the survey data.

Pipelines which do not have any form of CP may be surveyed by using a temporary DC supply and anode bed. Long pipelines frequently have more than one DC supply for their CP, requiring a number of synchronised interrupters to perform a survey. DCVG surveys are often combined with other techniques, such as CIPS and soil resistivity as part of a comprehensive corrosion protection program.

Performing a DCVG survey is relatively simple - students or recent graduates are frequently employed to collect the data. Interpreting the results is a little more complicated and this task is usually performed by a specially trained corrosion engineer.

DCVG surveys may be performed by pipeline companies themselves or, more usually, by independent specialists.

Retrieved from "http://en.wikipedia.org/wiki/DCVG"

Categories: Corrosion prevention

If one is doing the sloppy DCVG, then one doesn't need to have trained person collecting the field DCVG data. However, any Corrosion or Cathodic Protection Specialist knows that if the field data is sloppy then even the most experienced and well trained corrosion expert in an air conditioned office cannot make bad field data good. My guess is that the person that wrote this article maybe connected to Cath-Tech which is an Canadian manufacturer of I believe to be sloppy DCVG equipment. In CIS (close interval pipe to soil potential survey also referenced as CIPS) as well as DCVG the pipeline operator gets what is paid for. If the pipeline operator paids for sloppy CIS and DCVG, then the pipeline operator gets sloppy field data that is difficult to analyze and use to make sound pipeline integrity decisions. I have been asked in the past to analyze hundreds of miles of sloppy CIS data. I was doing nothing else during the analyze of the sloppy CIS data than making educated guesses as to what the field crew did wrong when they collected what was worthless data that couldn't be used to make any sound pipeline integrity decisions.

In order for the field data to be usable, the field personnel have to be well trained and experienced as any pipeline operator knows and NACE International does make it clear that one cannot take some college kid with no training and put him in the field and get any valid CIS and DCVG data that can be used to make sound engineering decisions on pipeline integrity.

The best CIS and DCVG field data comes from experienced personnel who are extremely highly trained in how to do CIS and DCVG field data collection. This remark in Wikipedia is not only not true but silly.

Who Invented DCVG?

DCVG is short for Direct Current Voltage Gradient. In pipeline external corrosion control a voltage gradient is measured by two reference cells in contract with an electrolyte such as soil connected to a voltage meter. DCVG is also a cell to cell survey technique.

DCVG is also a technique for finding coating holidays on a buried well coated pipeline. The term DCVG was first used to describe this technique of finding and rating coating holidays on a buried pipeline. However, the use of cell to cell surveys on a buried pipeline was nothing new.

Cell to cell surveys before the development of DCVG was used to find corrosion hot spot areas on bare buried pipelines per the net protective criterion. This use of cell to cell survey is more controversial than DCVG and it tends to be called Hot Spot Survey. The DCVG procedure does copy this Hot Spot Survey method when taking side drains at coating holiday locations to determine if current flow in the soil is toward the pipe or away from the pipe. If current flow is away from the pipe then the coating holiday has created an active corrosion cell. If current flow is toward the pipe then the coating holiday is protected by the pipeline cathodic protection system. This is a matter of polarity of the voltage difference of a reference cell on top of the pipe and another reference cell located at a 90 degree angle away from the pipe. Since current flow is from positive to negative, if the voltage meter shows a positive number with the reference cell located on top of the pipe being connected to negative terminal of the voltage meter then current flow is toward the pipe and the pipe is protected per the net protective criterion.

The DCVG method was invented by the late Australian John Mulvany, an ex telecomms engineer, in the early 1980s. He developed and refined the technique in conjunction with Dr John Leeds, a professional corrosion engineer from Kent, England. Today, the DCVG technique is universally accepted and has its own method formally defined by NACE International.

This is from Wikipedia. The controversy generated by Wikipedia claiming that John Mulvany and Dr. John Leeds invented DCVG which has resulted in a silly discussion on Wikipedia would be best solved by saying the following:

The DCVG method as a technique for finding and rating coating holidays on buried dielectrically coated pipelines was developed by the late Australian John Mulvany, an ex telecomms engineer, in the early 1980s. He developed and refined the technique in conjunction with Dr John Leeds, a professional corrosion engineer from Kent, England. Today, the DCVG technique is universally accepted and has its own method formally defined by NACE International.

To say that John Mulvany and Dr. John Leeds invented DCVG would be like saying that both invented cell to cell survey. Therefore I can understand the discussion that has resulted in Wikipedia on this matter.

It is true that the DCVG technique is universally accepted but to say that NACE International has a standard practice for the DCVG technique is not totally accurate. Yes, there are NACE International standard practices that mention the DCVG technique but there is no recommended practice as to how to do a DCVG survey. That is why there is so much controversy as to what is a real DCVG survey or a cheap cell to cell survey that is not really a true DCVG survey. Since lawyers tend to run NACE International and those lawyers are more concerned about lawsuits by those would would be upset if their DCVG equipment was suddenly made by a NACE International recommended practice only a cell to cell survey rather than a true DCVG survey; do not expect a DCVG recommended practice from NACE International anytime soon. So NACE International recommended practices speak of DCVG in a very general way making it possible for anyone to claim that a piece of equipment that does a cell to cell survey is capable of doing a DCVG survey. In later blog postings what NACE International recommended practices have to say about DCVG will be addressed but not now as this is an introduction to the topic of DCVG.

Assuming that the buried pipeline is protected using Impressed Current Cathodic Protection (ICCP - as most are), then any defects in the coating will result in electrical current flowing from the surrounding soil and into the pipe. These currents cause voltage gradients to be set up in the soil, which can be measured using a voltmeter. By looking at the direction of these gradients, the location of coating faults may be identified. By plotting the direction of voltage gradients around a fault, the type and nature of faults may be deduced. By measuring the localised soil potentials with respect to remote earth, a measure of the effectiveness of the Cathodic protection may be calculated.

It appears a Brit wrote this because of the way some English words are spelled the British way rather than the USA way; but it could have been a Canadian too. Wikipedia gets it half right.

Assuming that the buried pipeline is protected using Impressed Current Cathodic Protection (ICCP - as most are), then any defects in the coating will result in electrical current flowing from the surrounding soil and into the pipe. These currents cause voltage gradients to be set up in the soil, which can be measured using a voltmeter. By looking at the direction of these gradients, the location of coating faults may be identified. By plotting the direction of voltage gradients around a fault, the size of the coating holiday and the position of the coating faults may be deduced. By measuring the potential of a reference cell on top of the pipeline with respect to a remote earth reference cell, an active corrosion cell can be found per the net protective current criterion. [There is not time to deal with the IR Drop issue here and I will attempt to address that matter in a later post.]

The person who wrote the original Wikipedia article is using vague language it appears in an attempt to make it sound as if the procedure is more complex than reality. It really is nothing all that complex. Since Dr. Leeds typically attempts to make the simple sound extremely complex; maybe the person who wrote this article was trained in the DCVG technique per Dr. Leeds. I have been condemned as a Corrosion Control Heretic for making the topic too easy to understand for the common masses making it appear that Corrosion Control Experts are overpaid.

Frankly, this is one example of Wikipedia having a really poor article on a buried pipeline coating survey technique. I am running out of time so I will continue later with more blog postings on the DCVG technique of finding coating holidays on buried pipelines. What I will have to say on the topic will be controversial I am sure as this article as short as it is has a few controversial statements in it.