Best Practices: gasket inspection / examination 6

[daviwy]

Gents,

Morning, I am currently looking into inspecting / examining a few of our gaskets in oil and gas environment.

Does anyone know of best practice techniques for the inspection of gaskets?

All I can really think of is visual inspection technique but this will mean inspection thousands due to the vast locations of these items.

Mechanical & Operations Engineer
Oil, Gas & Power

 

[daviwy]

to add to the above:

material : Steel
Pressure: 6-30 barg
fluid: oil & gas fluids (condensate, gas etc), mineral oil, MEG, seawater etc
external condition: sea atmosphere and sea water (i.e. salty)
running condition: some cycling, some not depending on use.


Mechanical & Operations Engineer
Oil, Gas & Power

 

[Fzob]

IS your goal actually leak detection? That's a bit of a different animal than gasket inspection.

 

[racookpe1978]

Rule 1. If a gasket is not leaking, do not make it leak by taking it apart and looking at it to see if it is leaking or not. (Murphy's Law of Gasket Leaks: Let sleeping gaskets lie.) 8<)

Rule 2. If a gasket is not leaking, you will not see anything leaking from the gasket. If a gasket is leaking, you will see (hear!) something leaking into or out of the pipe. (Murphy's Law of Gasket Leaks: Leaking gaskets don't lie.)

Rule 3. If a gasket is leaking, taking it apart to see if it is leaking will require replacing the old gasket, and often requires cleaning and inspecting the two gasket faces. This will require a leak test to see if the new gasket will leak. (Murphy's Law of Gasket Leaks: New leaks will be found on older, previuosly good gaskets during a leak test of the new gaskets.)

Rule 4. Murphy's Correlary of Gasket Leaks: Taking apart one leaking flange between two other good flanges moves adjacent flanges, which will only begin leaking after the leak check is finished and operations begin.

Rule 5. You will have to polish or wire-brush the old bolt/studs/nuts to remove rust and dirt so you can re-assemble the old gasket connection and re-torque it properly. (But before they were taken apart, rusted bolts and nuts worked just fine.)

Rule 5. Murphy's Law of Leak Checks also predicts that some of the old nuts and bolts will need to be destructively removed, or be accidentally destructively removed while they are being removed, and have to be replaced. Plan on having replacements available, because you will always end up re-assembling some of the flanges on a Sunday night shift right before a Monday holiday before a Tuesday morning startup.

 

[Duwe6]

Wrap all suspect flange edges with wide impermiable tape. Punch a small hole where the hole can easily be observed. Observe the hole daily, then weekly, then monthly.

racookpe1978 covered all the reasons not to mess with nonleaking flanges. Considering he is a 'Nuke', he *might* just know what he is talking about. Onstream Engineers tend to overthink items, and turn them into 'issues'. Relax and let the flanges/gaskets 'tell you' how they are. Its pretty simple, until someone overthinks it.

 

[daviwy]

Fzob,
I was thinking of putting together a program to inspect our existing gaskets. This is because we found one of them leaking and they've all been in operation for over 25 years, 26 to be exact!

But with the information I've been researching and reading seems like disturbing a gasket is not the best idea. plus racookpe1978 thanks for your break down

Mechanical & Operations Engineer
Oil, Gas & Power

 

[ash9144]

Racooke covered it nicely.
Just one other point...Do not reuse gaskets if you expect them to not leak.

 

[BigInch]

Careafull. These things have some quantum properties; just getting too close to them can make them change state.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[racookpe1978]

To all: Many "tank you's" for the kind thoughts above.

To daviwy: Your thoughts of developing a leak check plan as a long-term preventative maintenance strategy are good; very good in fact.

Congrats on having so few leaks, and only finding a limited number now after so long a time!

Do a regular, systematic search of all lines. (You may even find that you don't have an automated (PC-based) line list and valve list yet. And one of the first things you may end up doing is figuring out: "What do I have right now?", and "Where is whatever I do have now?", and "What do I call whatever I do have right now?" and often comes before "What condition is what I have in whereever I have whatever I have?"

From a line list, by area of the plant - (Hint, start near and around the area next going down for maintenance or replacement or extension) - start recording the valves and the leaks. Then KEEP THAT LIST UP TO DATE with a monthly "Walk around underneath and look" and by more formal "Climb around and inspect" survey.

Get your boss and the plant operations managers involved, as well as the plant operators. They should get in the professional habit of walking around the plant at regularly - NOT just driving through to the next financial and quarterly stock meeting! - and they should be looking at problems and for problems.

Your "problem entry" screens to the on-line "Leak List" should be as simple and as easy to use as possible. As open to ALL plant operators and plant engineers and plant maintenance workers as possible.

Your goal should be "Record the problems" first; "Record as many problems as possible as easily as possible" second, and "Prioritize and plan for repairs" only a distant third. See, the obvious and emergency problems will get attention. They'll get fixed - or at least "band-aided" immediately.

You want your "Leak List" to be used as a long-term tool to plan repairs before the next outage, to stage money and time and parts and equipment and scaffolding and work crew assignments for repairs BEFORE the next outage in each section.

And, unfortunately, you will certainly find that some repairs, some leaks, are going to stay on the list "forever" .... So be it. At least they are written down.

 

[daviwy]

Thanks ever so much guys, I am also looking at trying to see which NDE Techniques I can use for inspecting these gasket, the funny thing is that the corrosion we're experiencing is aggressive on the outter side of the ring.

Nevertheless, very useful info and thanks very much gents. Now to go through the not so easy process of getting all these information from the terminals and offshore.

Fun and games!

Mechanical & Operations Engineer
Oil, Gas & Power

 

[Duwe6]

For a definitive analysis of your OD corrosion, send one or two corroded samples, and one new one, to a metallurgical test lab with Failure Analysis capability and an SEM -- Scanning Electron Microscope. When obtaining the corroded gaskets, take care not to disturb the corrosion 'bloom' on the outer ring.

 

[unclesyd]

You have plenty of time to workout some testing or inspection procedure for the outer ring on a spiral wound gasket.
In reality you don't need the outer ring once the gasket is installed and properly seated. This ring is for positioning and retention of the spirals until seated. The inner ring is a lot more essential to prevent lost of the spirals to the process. The secret of having a high integrity flange is to have the proper flanges, properly make up, and the right material for the spirals with a compatible filler material.

As posted above, visual inspection is probably the best method for leak detection. We couple ours with the UT line survey program.
On a lot of gas lines we use a Ultrasonic Leak Detector where conditions permit.

One very important point in surveying lines or flanges don't look up to the point where gravity will put something in your eye. Keep an angle between you and what you are looking at.
Also keep in mind Boudreau's Law, "It has happened and you just don't know about it"

Addenda:
Don't try this at home.
Some events with spiral wound gaskets resulted in leaks or just scared us.

I've posted this before, where 24" class 300 Spiral Wound Gaskets Graphite were used as a filler where Mica was called for NOX service. These flanges operated at 1250F @ 250 psig. There were no leaks and the problem was discovered when replacing a valve.

On short neck 24" manway flange green cloth tape was used to hold the gasket in place when installing the cover. The tape burnt up and we had a major leak on top of a heating fluid Vaporizer. 70 psig @ 700F.

This one is fro the books. In our polymer process we have a filter system that has to be changed out several times during the process of a run. The lines that bypass the filter a removed to be cleaned. The problem is that there are small differences in make up either requiring a Dutchman or reworking the line. The lines are jacketed with Class 2500 flanges operating at 600F and 2800 psig MAWP. Many years ago I was standing by when a bypass line was being replaced and upon breaking the center flange 4 spiral wound gaskets fell out. On checking with the lead mechanics this was common practice and he knew where 11 gaskets were used. As this practice had worked for several years I didn't immediately tell the Mechanical Engineering taking a little time to evaluate the practice. When I did show the mechanical Supervisor he turn white as the one is question was on a operating line. After several meetings and discussions the practice is still being used after 30 years. An effort was made to get the lines with the larger gasp repaired.

 

[gasketguru]

You may want to look up the process known as "LDAR" (Leak Detection and Repair) which is an inspection of pipeline components which is mandatory in US refineries and similar sites, and essentially involves "sniffing" of valves, pumps, flanges, open ended lines etc. using a flame ionisation detector to look for VOC fugitive emissions. (It is the light ends that leak more thn the heavier compounds of course.) Obviously this only applies to your hydrocarbon lines, not water, and glycol whilst theoretically being a VOC is not that easy to detect (though gas dissolved in glycol streams does show up in joints that are giving emissions).
Having done a lot of LDAR survey work myself, I would say that typically large joints are more likely to leak than small ones, though there are less of them, and things subjected to thermal cycling and perhaps vibration (suction / discharge lines on compressors for instance) tend to be more likely to be found leaking. A good LDAR database can be invaluable on-site as might show repeat leakers, help grade gasket and packing suppliers and the fitters as well perhaps.
Corroded components are common on coastal gas plants but should be easy to spot, and as has been said already if it isn't broke then don't try to fix it, b ut be wary of pressure containing parts that might be badly corroded of course. However, if some emissions are modest (i.e. valve glands that can be nipped up) then sometimes an early first-fix can be useful, and save larger leaks from developing. However, do be careful with flanges having compressed fibre joints as these can embrittle and could crack if disturbed.

 

[PAN]

Lesson learned about gasket inspection...

http://www.h2incidents.org/sort.asp?cri=3:11&x=30&y=6

 

[PAN]

This incident is for the specific subject.

http://www.h2incidents.org/incident.asp?inc=291&cat=8&val=4&cri=8:4

 

[daviwy]

Gents thanks for all your comments, really have been useful.

I've put together an inspection program now which will be rolled out through the fleet.

Mechanical Operations Engineer
Oil, Gas & Power

 

[abeltio]

I've used ultra-directional microphones to detect leaks it works really well and do not need to stay close to the leak.

saludos.
a.