B31.3 345.3.1 (b) Joints Exposed Question 1

[302Hugo]

Hey all. We are looking to re-rate a section of piping to a higher MOP. Currently all of this piping is insulated and I am trying to determine if I need to remove all of that insulation or if I can test in place. Our new MOP will still be lower than the ANSI rating for that section (why they only tested to like 1/3 ANSI rating years ago, I don't know.) and the integrity of our piping looks good, so I am not too concerned that we would have a leak and that examination of the joints would be crucial, although good engineering practice. However, I need help to interrupt 345.3.1 (b) for you knowledgeable folk . When it says "Joints previous tested in accordance with this Code may be insulated or covered" can I assume we fall under this since it was tested previously. However, it was tested to a lower MOP so that is where I question it. Or is this point referencing the situation where it was tested to my new MOP (in a shop for instance) and then insulated, brought to site, then tested in place (why you would do that after testing in the shop I am not sure?)?

 

[XL83NL]

Wouldn’t the main question be to determine if B31.3 applies here, rather than e.g. API 510?
B31.3 is for new construction. Based on your post, it seems this is existing pipe work. Has it already been in service, or has it just been insulated and needs a quick modification prior to putting it into service?

 

[1503-44]

I would say that you do not have to reinspect joints, unless you have reason to believe that they need to be reinspected. Just do the hydrotest at the appropriate test pressure to requalify for use at your higher pressure.

 

[XL83NL]

Just do the hydrotest at the appropriate test pressure to requalify for use at your higher pressure.

Why? Whats the justification in that? Have you considered all the Code requirements then? B31.3 is more than a hydrotest code ...
Think of the scenario where this pipe work still is (considered) new construction. The line class pertaining to this pipe is designed for a maximum pressure (or 'MAWP' if you like - even though MAWP is not a B31.3 term) for 300 psi. You do the hydro @ 450 psi. Is the system than suited for say 400 psi, since you hydro-ed @ 450?

 

[LittleInch]

302 hugo,

Your OP comes across as being rather flippant and lacking in detail. The fact that you "don't know" why something was done in the past tells me you don't know if the reason was justified or not. You have to assume that it was done for a reason.

Raising the MOP of any system requires a comprehensive review of the components, examination of its current condition and a field examination of any component attached to said system.

Such review should be documented in a MOC procedure, reviewed and approved by the owner and any other jurisdiction.

Especially for an insulated system, most of which are notorious for unseen corrosion, I would have thought that you would need either removal of all insulation or internal inspection using a suitable tool to establish remaining wall thickness.

assuming you've done this but just not told us, I believe that you need to follow the wording as though this was a new fabrication.

The item b is there for the reasons you posit - i.e. sections of piping tested in a shop don't need the full strength test (but usually need a leak test for the joints).

However you're changing the test pressure so those items have not been examined before at that test pressure.

It's a pain, but the text IMHO, doesn't give you a get out if you want to say that the piping conforms to ASME B 31.3.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Even though constructed under a different code, pipeline work coats the pipe then buries the pipe, then hydrotests the pipe with all joints hidden from plain sight. You will know if it leaks one way or another. And anyway, it is not only joints that are subject to corrosion. That can happen anywhere under the insulation. Will you strip all the pipe from end to end?

There are many cases of rerating pipelines to higher pressures (including unpiggable pipelines) done without digging up every single one of thousands of joint just to have another look. Even if necessary, you might consider spot checking. strip a few locations and evaluate if the inspection results of those suggest that more should also be stripped.

 

[LittleInch]

I agree it's not the same but then buried pipelines are usually subject to CP protection and uprating a pipeline without internal inspection becomes really quite difficult.

This examine the joint / weld thing in B31.3 is rather odd, but on an above ground piping system not too onerous compared to buried pipeline.

The question is a bit academic and is more about observing the letter of the code to avoid any issues further down the road. The observe each weld thing is more about the fact that you can do it to observe any weeping from a crack rather than when it's buried. Small leaks / drips you would never see on a pressure graph.

The "previously tested" exemption could be argued both ways, but for me - it's a different (higher) pressure) therefore it's like a new pipe. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[302Hugo]

Thanks for everyone's input, much appreciated. To answer some of the questions/comments:
XL83NL - Good point, however I believe you mean API 570. I will have to look into this. It has been in service.
LittleInch - Sorry, I didn't think much detail was required as I was only concerned with this specific section, and didn't think it was pertinent to explain our whole engineering evaluation, but as XL83NL pointed out I may be looking in the wrong area to begin with. Again I didn't think the details were necessary for the question, but the reason I don't know why they tested to a lower MOP is because there is no documentation to show why. The drawings do not state why. The thought/assumption with everyone I talked to is that the thought process at the time was to only design to a pressure appropriate for the operation and not test to full MAOP. Nothing in this system is pointing towards a pressure limitation. In regards to an evaluation of the system, yes we are planning on completing examination checks and doing our engineering review (MOC, examinations, etc.) to ensure it is fit for the pressure increase, and eventually we will get the inspector process started. At this point I'm just trying to gather information on the proper way to proceed. With that all said, I think you are correct in your interpretation and that it for like a shop tested spool.
Ax1e - Yeah my area of better understanding is CSA Z662. The thing about pipelines is that you would have ILI information which gives you a clear picture from trap to trap. You wouldn't have the same with an unpiggable line. I could be wrong but the regulators will require an engineering evaluation before approving, just like the regulator would for the B31.3 piping.

 

[1503-44]

I doubt that anyone will expect you to strip the pipe clean for more than a spot check of a few joints at most unless there has been a history of corrosion problems in your or similar systems. If you have doubts, try making contact with the regulating authority asking them what they have required for previous rerates of similar systems.

Not all pipelines, by a long shot, are piggable still today and as I have already said, many unpiggable lines have been rerated to higher pressure based simply on SCADA records showing the highest operating pressure experienced during the previous year's operation, without even doing any new inspections or hydrotesting at all.

 

[DekDee]

ax1e,
Please correct me if I am wrong but all the pipelines I have ever worked on required 100% RT.
B31.3 NFS only requires 5% RT so there is a big difference between pipeline codes 100% coverage (admittedly with much more lenient acceptance criteria) and piping in a refinery that has only experienced 5% coverage.
Regards,
Shane

 

[LittleInch]

ax1e - I know we're going off topic here, but your answer on the uprating makes no sense to me.

If the scada records show that the pipeline is operating a pressure higher than it's MOP or MAOP then this is surely wrong.

To use numbers if your pipeline is designed / pressure tested to a DP of say 700 psi then it can't operate higher than that.

If you want to up rate it to say 1000 psi, the fact that it has been operating at 650 psi is not relevant.

Re-rating is sometimes subjective, but a lot depends on the actual previous hydrostatic tests undertaken. It could be the uprating is still within the MAOP, which for the ASME codes is set as a fraction of the test pressure. How you re-rate existing equipment is or should be a set procedure with checks and approvals based on data.

DekDee - Many liquid pipelines are not 100% RT, the design codes allow down to 10% (e.g. B 31.4 434.8.5). Most gas lines are 100% and some companies do 100% on all lines, but worldwide it's not universal by any means...

302Hugo - Thanks the response - too many posters just say "Thanks for the info..." with no real follow up.
Glad to hear that it's being done properly - we get a lot of posts here which are not so good. Details are optional, but could have been mentioned in passing that that side was being taken care of. No worries.

Yes a hydro test will cover a lot of issues which may not be seen unless you strip the pipe of its insulation. It only takes one location to fail, but you know your system a lot better than us. A lot will depend on location, length, difficulty of removing insulation etc etc to make a judgement as to whether you just hydro the thing and see what happens or undertake a fuller inspection.

Good luck.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XL83NL]

So much replies are related to pipelines, whereas the OP clearly referenced a B31.3 section in his first post. Can we get back to topic? were getting a bit off topic here.

 

[GD2]

302Hugo,

You can't jump to re-rate the piping because it was running at lesser MOP and looks good.

To re-rate you need to follow API 570. This is required because after placement in service, lots of internal and external (internal corrosion/erosion, external environmental conditions) plays the dynamics. At the end of the day, it is the thickness available to take the higher pressure rating. There could be spots where corrosion/erosion will be much higher than a straight pipe. API 570 spells out of details about it. The evaluation/assessment part is spelled out in FFS-1/API 579-1. For ASME Pipelines - B31.4, B31.8, many times a simpler option ASME B31G is used.

Doing an evaluation is by no far means is an easy task. At the most, you might be able to do Assessment level 1 and 2 at the field level.

The Regulator will surely need to see an engineering assessment before the approval is given.



GDD
Canada

 

[KevinNZ]

Why is corrosion only coming to the a discussion about increasing the design pressure of piping?

If the pipe is corroding then this needs to be assessed first in the context of the original design pressure and corrosion allowance. Is the corrosion with the original allowance?

Now when the line is redesigned for higher pressure the design needs have a corrosion allowance. This can the same as the original or changed depending on what is found in the line.

The redesign needs to repeat all the original design calculations, including but not limited to , hoop stress, sustained, thermal range and occasional loads. These all have pressure terms. Only then would you look at pressure test requirements. Depending on the code an new pressure test is not an absolute requirement.

 

[GD2]

302Hugo,

It could be difficult but can you find out the original application for MOP approval by the Regulator? Was it to the full flange rating or the 1/3 hydrotest you stated in your opening post? It could throw a whole line of discussion.

if you had the MOP approval for the flange rating and have an inspection program in place, I believe it will be lot easier to convince the Regulator and run the piping at higher pressure.
But if the approved MOP was at a lesser pressure (MOPs are confirmed by a hydrotest), you will have to go through a lot to re-rate the piping.

GDD
Canada

 

[XL83NL]

What do MOPs have to do with B31.3?