Hydro

Date 11-09-2013 07:48

Jim,
Where I work we build ASME code vessels/exchangers and we don't have start and stop times on our test report. We have hold time which is usually 1hr+. If our customer requires time we use a chart recoeder to show testing length. We also have a remark section for any other requested info.

Regards
J.W.

By welderbrent (*****)

Date 11-09-2013 14:03

WOW! I have been involved with a number of hydro tests and none was anywhere close to that duration. But, it does all depend upon the code, the job specs, the customer requests, as well as the product to be tested.

Have a Great Day, Brent

By js55

Date 11-09-2013 16:06

ASME generally only requires 10 minutes.
I am seeing 8 hours in many of the oil and gas specs.

By CWI555

Date 11-09-2013 11:20

It can be recorded two ways. Start stop time, or total hold time. Either gets you to the same end. 0900 - 1000 1 hour, or 1 hour hold etc, there is no difference except in how your client or code may want it recorded.

By 803056

Date 11-09-2013 14:31

We had a customer specification that required an 8 hour hold time. It wasn't vain, the vessels had large diameter (40 inch) covers that developed several leakers around O-ring seals after holding the pressure for several hours. It is a function of the leak rate, i.e., many leaks are slow enough that it takes time for them to become detectable. Small machining imperfections in the O-ring groove provided a very small leakage paths that required hand polishing to remove the small nicks that allowed the leakage. Had the hold times been limited to a short duration, we would have assumed the seals were good. Customer complaints would have resulted had the vessels been shipped in their original condition.

Best regards - Al

By CWI555

Date 11-09-2013 18:01

I believe the longest hold time I've witnessed was 24 hours. That was an aerospace application for a cryogenic hydrogen tank. Either way, the total time required could be recorded two different ways.

By 803056

Date 11-09-2013 21:56

How did you detect the leaks should there be one? Hydrogen is pretty darn small, so it will find the smallest of seeps given sufficient time.

Al

By CWI555

Date 11-10-2013 01:38 Edited 11-10-2013 01:55

It's not that hard. There are multiple methods for hydrogen leak detection.

Thermal conductivity - Utilizes a background gas with a different background conductivity.

Electrochemical - A liquid electrolyte is placed on the opposite side of a gas permeable membrane. Doesn't work well with higher temperatures, but for cryogenic application, it works well.

Mass Spectrometers/Gas Chromatographs - Especially continuous flow mass spectrometry. A variant of which is what we utilized.

Semi-conducting Oxide - This was developed for higher temperature detection. Where the electrochemical variation fails, this one succeeds, but it's not a good option for cryogenic work.

They can be combined, varied etc, but the difficulty isn't the problem with them. The difficulty is in the expense. All of the above, especially the continuous flow gas source mass spectrometry unit we utilized (millions worth).

As for the size of hydrogen, only Helium is smaller. In picometers He = 28, H = 31, F = 57, Ne = 58. After that, it gets pointless. For the particular vessel in question, the hold time assumed a leak, with acceptance based on quantity over time.

Edit: While government/aerospace specialized applications like mentioned here exist, the global market is in terms of 233.7 billion cubic meter projected for 2013. It is expected to increase by 4.1% through 2016 making it 286 billion cubic meters. At the rate it's climbing, and being in favor by the global hysterical err warming crowd, it would be wise for the younger crowd of inspectors to get familiarized with the methods and science of inspecting for leaks. Governments around the world are licking their chops at the prospect of something else to regulate, and this makes a very easy target given the potential volatility of hydrogen and liquefied hydrogen.

By Metarinka (****)

Date 11-18-2013 03:26

helium checking is probably the most common way to test pressure or vacuum chambers for leaks. You fill the vessel with helium and probe using a mass spectrometer. It is true that it will find very tiny leak paths, but it is not impossible to make a vessel that seals hydrogen or helium for the long term. Generally the wall thickness is over sized for the pressure, and even then with a metal sheet you assume a very small leakage rate right through the metal, hydrogen will mitigate down the grain boundaries, impossible to stop that.

By swsweld (****)

Date 11-10-2013 17:53 Edited 11-11-2013 19:00

Jim,
Our forms have start/end time and temperature, the high and low psi and intermediate times and temperatures when doing a 1-4 hour test. 10 minute test only require start and end numbers.

The forms differentiate between shop or field hydro test and have pertinent info like required test pressure, max test pressure, test duration, spec section (customer specific) and referenced code. We generally work under B31.3, 31.4 and 31.8 and occasionally pressure vessels.

Digital chart recorders (pressure, time and temp.) are required on field test over 1 hour.

We only use Digital Pressure Test Gauges so the Gauge # is recorded on the form and the calibration info.

There is also a comment section on the form that could be used to explain any spikes in pressure or other conditions that might alter the test numbers.

It is so sensitive that, in the hydro shop (70F controlled) even opening the door might cause a decrease by 5-15 psig on a small spool. This is at the North Slope there are additional considerations due to the climate.

By Joey

Date 11-11-2013 05:07 Edited 11-11-2013 06:00

If start & end time are in the form, you're oblige to indicate it.
I will modify the test report form to remove the start and end time if no relevance in the hydro test procedure.
Just indicate the Holding time, to avoid the Risk of being question by people not familiar with the test (e.g. why you did the test in the afternoon, the weather is cooler in the morning, who monitor the testing during lunch time? are you sure the Inspector is present during the time of test? I saw him in canteen during the period of testing, can you indicate the appropriate timing in your procedure? etc).

~Joey~

By swsweld (****)

Date 11-11-2013 14:37

Joey,
It's true that the more info provided to the client the more responsibility you have to follow and document it. Some of our hydro info is client based requirements and the rest is our company going above and beyond the clients requirements. The client isn't as production driven as much as they are safety and quality driven so it works here but not with every customer. We, (QC) have to verify the start and end of the test but do not have to be there for the full test as the hydro technicians do. You bring a valid point, giving more info when not required or necessary may only hurt you.

By Jim Hughes (***)

Date 11-11-2013 14:44 Edited 11-11-2013 19:24

Thanks everyone.
I'm one of 15 different DQM's (district quality manager) for the company I work for. My reason for asking is, as a company we are going through all of our forms and reviewing the required info to try to standardize all of our ITP's, procedures and forms. Since we are set up in districts we had a number of different forms to review and deside on standardization. The topic of a start time and end time came up because some of the other DQM's did not have that on there report forms. In the process of trying to get a concensus, I thought I would bounce it off some of you SME's. But as indicated in the responces there really is no SOP. I have been performing hydro's in some sort of fashion for 25 years, and have used chart recorders for exstended hydro's. But for our standard plain jane ASME B31.1 or B31.3 hydro's it is 10 min. Chart recorder use for short hydro's are possible but alot of times, not practical for field use.

thanks
Jim