We at our plant suffering the problem of plant air shortage due to suspected leakage. Although as per design one of the air compressor is standby. But it is also continuously operating along with other compressors and there is no standby. The shutdown of any one of the compressor, causes production loss for the plant.
We want advice from people who have got experience in detection and fixing of air leakages on the plant using Ultrasonic detectors. We are thinking to carry out a leak detection survey at our plant, and need expert advice / assistance...
Best wishes
Mohammad

It can be done very successfully, if a few things are kept in mind:
-air leaks are high frequency, and as such, bounce off walls very easily. Make sure to test in multiple diections to pinpoint the leak.
-The best time to begin is when an area or process is down. You can often find the largest leaks then.
-Sometimes the leak in needed, as in some solenoid valves, or processes where air loss is expected.

The most important thing to keep in mind is the system, not the leak. Sometimes putting in air storage tanks, or accumulators, near where the air is needed is effective. Sometimes piping is not of the correct diameter to move air around in a facility. Most plants have a large manifold, which splits into smaller diameters, which is piped into even smaller air lines. Each restriction lowers not only the volume of air which can reach the process, it restricts the speed in which the required amount of air can reach the process. Air is confined by the same physical restrictions as water. It can only move so fast in a given diameter at a given pressure.

Operator ignorance can be a factor as well. Most people see air as "free", not realizing the cost to pressurize it, clean it, dry it, and move it to where it is needed.

There's much more, as I'm sure you'll probably see from other posters who know much more than I do.

There are also companies who specialize in looking at compressed air systems to maximize their efficiency.

Stan gave you some very good advice.

I can add that ultrasonic leak detectors are inexpensive, easy to use and that I read a survey that reported compressed air as the most expensive utility. That makes it easy to justify to management.

Good Luck,

Compressed air systems are about 14% efficient, in the best cases (~9 hp to make 1hp of air). Air leaks are one of the single largest energy opportunities within a facility.

Lots of great, free, information, software, tools and case studies on the application of air surveys (amongst other things):

http://www.oit.doe.gov/bestpractices/

Which is a US Department of Energy website. The tools and materials were developed by end users, vendors and the US DOE and made available for all who wish to use them.

You can also download my "Industrial Assessments" book (free) from http://www.motordiagnostics.com/presentations.htm

In the later part of the book, I cover the calculations, charts and tables for determining air leak cost and several air-system related strategies.

Howard

Howard, where did you get the ratio of HP to SCFM? We have some centrifugals that we have measured with a much better ratio - closer to 3.5 HP per SCFM. Are you counting drying, controlling, and system cost as well?

Not disputing - just wanting to learn more

Here is a good site for products, links, and references on compressed air:
http://www.leakzone.com/

A compressed air leak survey followed by correction and air system adjustments can very quickly pay for the costs of instruments, labor and materials.

Thanks for all of you for giving your valuable comments and advices.
I appreciate any further comments from other posters on the forum.

Now I want to ask a question from Mr Stan Riddle.
Mr Stan.. as you have made comment that
Quote
"There are also companies who specialize in looking at compressed air systems to maximize their efficiency."
Unquote.
Can you send me the information / contact about such a company, which can carry out a survey on our plant in Qatar.

Mohammad, please email me at scout655@yahoo.com, and I will reply with the company we used.

I have worked with major a compressor company over the last year in performing air system audits at some of our plant locations. Their system auditors have done a great job of making our systems more efficient. You have to be careful about only correcting air leaks. Alot of times by fixing your air leaks you increase system pressure which create more leaks. The company that has performed our audits have been shutting down some major hp. usage. And at the same time providing constant air pressure throughout the system to + or - 1 PSI. In some cases we will save $120,000 a year with a $60,000 investment on sysem up grades. What we have found most of the time is that we are increasing air pressure to make up for lack of volume. I have seen plant air pressure lowered as much as 20-25 PSI with volume and piping corrections. If you lower your plant air pressure that much, most of your leaks will take care of themselves.

Stan:

It was the industry/ US DOE published average system efficiency. 9 horsepower in and an average of 1 horsepower at the point of use.

Howard

Can we apply ultrasonic to detect internal passing of oil & gas wellhead valves such as follows:
1) Non Return Valve
2) Surface Controlled Sub-Surface Safety Valve
3) Manual Master Valve
4) Crown Valve
5) Surface Safety Valve
6) Wing Valve

TQ

This sounds like a repeat question but want to confirm before buying the unit: Can we use ultrasonic detector to detect passing of a non-return valve (which is supposed to prevent reverse flow) let say in natural gas service? Any valve size limitation? Rgds

Josh,

You ask if

quote:

Can we apply ultrasonic to detect internal passing of oil & gas wellhead valves such as follows:
1) Non Return Valve
2) Surface Controlled Sub-Surface Safety Valve
3) Manual Master Valve
4) Crown Valve
5) Surface Safety Valve
6) Wing Valve

Item 2 is downhole, so I suspect conventional ultrasonic instruments wont help. For all items that are accessible on your Platform it should be possible to use portable ultrasonic instruments to detect internal leaks. Get the vendors to give you a demo. Background noise does not matter, so dont worry about that.

Dont buy anything till you do field trials.

V.Narayan.

Regarding comment by Vee: "Background noise does not matter, so dont worry about that."

Background noise is Very important with ultrasound measurements; whether using a contact probe or microphone. Audible sound (what you hear) is not the same background as ultrasound because of the different frquency range. This difference is often part of the "sales pitch" showing the advantages of ultrasound (I demonstrate this often!). Carefull measurement technique may be required to minimize the effect of ultrasound background or to be sure you are measuring what you think you are.

There are remote contact sensors available for the downhole valve, but temperature or space restrictions may not make its use feasible.

The better advice is to get a demonstration; preferably by an expert and not from a salesman/saleswomen. You have nothing to loose by borrowing or renting an instrument and conducting your own evaluation.

Walt

Walt,

Thanks for the correction. I was under the impression that most modern instruments are tuneable and remove the effect of background noises. That was the basis of my comment, apologies to Josh.

V.Narayan.

We have recently purchased an ultrasonic
detector, CSI's Sonic Scan 7000. To set the
priorities, what should be done to look for the largest leak? What to start looking first?
Can you give us tips for the leak testing procedure.
Will appreciate comments from experts.

Mohammad, it looks like you are living in a hot country. What is the average humidity and surrounding temperature? Is your compressor house well ventilated? Do you have a suficient supply of cool air? Is the heat generated in the compressor house removed easily?
Are the compressors sized by a company specialized in tropical conditions?
We also learned the hard way that "normal conditions" in western regions are never met in "hot" countries . After seven years operating two screw compressors, we had to replace them and relocate the compressor house.

Svanels, You are right. This region of world is hot with the average humidity 80-90% at a temperature averaging at 40-45 deg C. Ventilation of compressor house seems to be sufficient. I don't know that whether the company (who sized the compressor house)is specialized in sizing for tropical regions? But you might be right. I need to consult some one specialized in sizing for this region. If you know such a company, please inform. Cheers...

Hi Mohammad,
Your temperatures sound like summertime in Arkansas!
I used UE equipment to do an airborne ultrasonic survey of our compressed air system. I found over 150 leaks of all sizes. One major leak was caused by tractor damage. The resulting leak was made 100 feet away at a weak joint.
I categorized the leaks as:
A. Major leak in >= 4" pipe.
B. Major leak in >= ¾" and < 4" pipe.
C. All minor leaks
It was instant gratification with this survey. When I found a problem, there was no need to use other technologies to know the problem was real.
I had a couple of instances where, when the first leak was repaired, a second leak was discovered. This happened where there was limited access to either leak through guards and one leak was in front of the other.
A follow-up retest is a must. An attempted repair in one 4" line moved the leak from a soldered joint to a threaded joint. In another instance, the workorder was closed out but the Class B leak was still there.

This article appears to augment answers to some of my questions on valves raised earlier and pasted here to share with everyone else:

http://www.enerchecksystems.com/articl25.html