Criteria for hot-torqueing in a plant that cycles very frequently 3

[Mous1747]

My plant cycled 29 times in the last 18 months, you can imagine how much problems this is creating from downtime and lost production to equipment failure....etc.

One of the problems we are facing is flange connections are getting impacted by all these temperature transitions, thermally affecting the bolted joints causing it to leak.

we are trying to establish an inspection criteria to leak detect flange connections using fluke ultrasonic but most importantly we also wanting to establish criteria for hot-torqueing or turn-of nut while online or between cycles to avoid leaks all together.

What is the frequency to go back an tighten the nuts while online? what would be the optimal duration ?
if waiting for another plant trip , is it going to be every two trips ? or 3 or more?

I appreciate all your inputs.

 

There are no easy answers for these kinds of flange leaking issues. I suggest you escalate this to the level of retaining a specialist consultant engineer. The expert needs to see your entire system in person and learn the history for starters.

But (as a non-expert) I have a feeling you might never be able to entirely eradicate this problem, given the operating conditions.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[r6155]

Can you send us more data?: temperature, type of gaskets, materials of bolts, flange class, etc.

Regards

 

[MJCronin]

Mous1747...

You posted in the B&PV forum, so I am guessing that your question is a power plant issue ??? .... How old is your plant ?

Can you tell us more about the type of plant and, more specifically, the piping and boiler systems that are giving you the most problems ?

Is this an older Combined Cycle plant that was originally designed for baseloading but now is being forced into frequent shutdowns and cycling ?

Over the past couple of years, POWER magazine has been covering specifically the dark underside of renewable power systems - i.e. the accelerated degradation and failure of the "load following" plants necessary to maintain a stable electrical system.

I strongly agree with the comments of "Ironic Metalurgist" above.... Contracting with an experienced, bolted joint consultant would be my choice.

Additionally, some contractors have developed their own specialty tooling and methodologies for "hot bolting"

https://www.patriot-international.c...10/Flyer-HotBolting-Patriot-International.pdf

Please tell us more and keep us involved in this important topic !!!

Thank you and Best Regards

MJCronin
Sr. Process Engineer

 

[saplanti]

You can use strain controlled bolt connection instead, or use spring washers to keep preload during the thermal cycles.

https://www.tandfonline.com/doi/abs/10.1080/15367730500374381?src=recsys&journalCode=lmbd20

https://www.aspseal.com/Valve-Packing/pdf/Using_Bellville_springs_to_maintain_bolt_preload.pdf

 

[r6155]

Meanwhile waiting for more data from (OP),an alternative is the welded membrane gasket or welded ring gasket. See Flexitallic joint design criteria.

Regards

 

[MJCronin]

Mous...

FIRST:
Your term "hot-torqueing" is also often called "hot bolting" in the industry and on the internet. Whatever you call it, it is a very, very hazardous operation. Personnel have been injured and killed when hot bolting is uncontrolled. Competent, responsible companies in the Oil and Gas industry often develop detailed evaluation criteria that they will stand behind.

An example is here:

https://www.scribd.com/document/266519607/Hot-Bolting

(Pay attention to the superb Table-1,2.... Not all flanged joints can be "hot bolted" and some require pressure reduction to the piping system !)


SECOND:
"Hot Bolting" sometimes also includes complete replacement of a defective stud/bolt/nut while the piping system is operating. Usually corrosion has affected all fasteners on the particular flanged joint, so this activity is quite different from trying to "snug-up" a joint to stop a leak. This is sometimes done for corroded fasteners, but I assume that this is not your issue. Is that true ?

THIRD:
What is your record keeping system to address these issues ? How are you keeping track of things ? Are individual bolted joints identified and are they repeatedly leaking over time ?.... In my opinion, these bad actors will never be fixed an probably require gasket replacement and/or flange replacement.

FOURTH:
"Hot Bolting" has been around for a long time and there have been different approaches taken by Management to address this important issue. Are the reptiles in your plant management structure willing to develop a consensus guideline, take responsibility for it and sign the coverpage ?..... OR will they keep things on the sly, pretend that it doesn't happen an then blame the most recently hired newbie ? BP, as noted in the link above takes responsibility ...

Please tell us more about your specific issue and how you intend to incorporate the advice you gain into a plant practice..

Best Regards

MJCronin
Sr. Process Engineer

 

[EdStainless]

First, are you sure that your cold torquing method is producing the desired UNIFORM compression of the gasket.
You know, good clean bolts with uniform lubrication, cross pattern, increasing the torque in three of four steps, repeating the final torque two or three times.
If they are not right to start with you have no chance.
You may need to look at alternate gasket materials. And the use of Belleville washers is another good option.
I would select a couple of joints that have given the most trouble and fit them with instrumented bolts.
This way you can monitor those and see what is actually happening.
Monitor the actual tension as the plant cycles.
Hot bolting is a very high risk operation, think of it as splicing a high voltage electrical line while energized.
It can be done, but should be the last option.

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P.E. Metallurgy, consulting work welcomed

 

The science and technology involved in making a sound bolted flange connection is a near bottomless well of complexity. Adding temperature cycling and hazardous fluids to the mix greatly complicates it. For non-critical, smaller bore piping joints it's usually not a problem.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Mous1747]

the plant is really old it's from the 60s however this particular line was replaced back in late 2019 ,this was the last time the flange assembled. this is a fertilizer chemical plant
the flange is not part of a vessel or exchanger it's a 10" piping. the temp is 1100 F pressure 350 psi all CS raised face, B7, flexitalic Spiral wound

We do have a a really good procedure based on PCC-1 for flange assembly and torqueing but not sure if it was followed.

i am not really sure what caused this flange to leak, but we know for sure when we inspected it was loose or under-torqued.

also when the flange was inspected the gasket was in a really good shape, i know that doesn't mean anything but at least it wasn't damaged

I am sure if i explore better gasketing options in addition to using Belleville washer this will improve

but i am really curious to understand the direct effect of heat cycling on the torque or preload ? when the plant shutdown temp will drop from 1100 F to maybe 400 F in an hour. and during startup it will go from ambient to 1100 F in about 7 hours.

 

[r6155]

Ummmm!! 1100°F and 350 psi !!!
Can you tell us the Class of flanges? and the actual bolt diameter?
Are you sure of the material you mentioned ?

 

[LittleInch]

t will depend on what happens to this flange under this rather high temperature load from a pipe stress point of view. Does it have a tensile or compressive axial load? Does it get additional moment or torque due to thermal loading?

The bolts themselves will expand and hence reduce the clamping force on the flange which should have been allowed for in the design.

How are the bolts "torqued"? Torque is a poor judge of axial force in a bolt as it is dependant on so many things which vary. If you want true axial force then you need to use hydraulic bolt tensioners.

It does seem a bit odd that something this hot doesn't use some form of belville washers or similar.

Ultimately though, the plant pipework should start leaking just because you're going through a few cycles of heat up and cool down...

Also my understanding is that this isn't "hot bolting" which is removal of bolts whilst under pressure, but trying to tighten them up whilst leaking a bit??

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

 

[EdStainless]

Knowing the actual temp of the bolts can also be helpful.
The last one of these that had issues with was at similar temp.
While running the bolts ranged from 400F to 900F because of airflow around the flange.
This was causing a prying action that was distorting the flange and leaking.
We added a little insulation to the cold side and got things more uniform, it fixed it.
You should also very carefully measure the flanges, confirm that they are flat and parallel, at least while cold.
Checking the variation in flange gap when hot may also point to issues.


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P.E. Metallurgy, consulting work welcomed

 

[MJCronin]

Soooooo ......

We learn a tiny bit more ...

You tell us your Carbon Steel ASTM A193- B7 studs/bolts are operating at 1100 F ? This is hundreds of degrees above the recommended temperature operating range. I believe that you are destroying your bolting materials through either creep or high temperature scaling.

An Excerpt from the superb inspectioneering website:

https://inspectioneering.com/journal/2004-07-01/3355/99-diseases-of-pressure-equipm

For carbon steel the oxidation temperature limit is usually in the vicinity of 900F (482C) - 950F (510C) range and above the 1000F (538C) -1050F (565C) range carbon steel starts to become limited in usefulness as a construction material because of excessive scaling over time. However, even before we reach these temperatures, carbon and low alloy steels are often limited by other high temperature metallurgical concerns such as creep rate, potential for creep-cracking, short-term tensile overload, and some forms of embrittlement like graphitization. Temperature cycling and intermittent service exposure may also affect the material selection.

You have some better choices for bolting materials including B16 and B8/B8M:

http://www.wermac.org/bolts/a193-b7_a320lL7_studs.html

You have not told us anything about your flange design ..... Its a WNRF, I hope .... Right ? ..... It's not one of those shit slip-ons, is it?

Please completely describe the flanged joint, flange face and gasket selection ... We cannot help you if you will not work with us ...

Post pictures of the failing joint, how it is welded and pictures of the failed studs/bolts if you have them ...

In my opinion, the use of Bellville washers would not be a good choice for a bolted joint where the bolting materials are operating in the creep range..... they only delay failure.

https://www.leespring.com/learn-about-belleville-washers

Be respectful of those who are trying help you ..... Tell us of your final solution and the reasons for your choices ....

Mous1747...Do you have any interest in completing this thread or have you dropped the discussion because you got what you want ?



MJCronin
Sr. Process Engineer

 

[MJCronin]

As fate would have it, there is an article about "Hot Bolting" in the current issue of Chemical Engineering Magazine ...

https://www.chemengonline.com/hot-bolting/

This superb article was written by probably one of the finest remaining B&PV engineers, Walther Stikvoort (Retired)

It is important to recognize that, similar to the restrictions contained in ASME PCC-2 Stikvoort agrees that not all flanges can be "hot bolted" and,...... by extension, not all piping flanges can be "hot torqued"

Again.... my opinion only

MJCronin
Sr. Process Engineer

 

[chicopee]

About reducing the cycling events by lowering the firing rate to the boiler or by installing a steam reservoir instead of banking on the boiler steam space. My only observation of a steam reservoir was with a steam train station in which a steam train dedicated for yard movements of trains and railroad cars. That particular steam train would be recharged every morning with pressurized steam.

 

[curtis2004]

Hi Everyone,

I have glanced to ASME B16.5-2013 (I don't have a copy of latest editions) pressure-temperature tables and found out the following:

1. Group 1.1 materials table ends at 1,000 F and recommended not to be used above 800F almost for all materials. Only Class 1500 @ 1,000F rating (430 psi) is above 350 psi.
2. Group 1.2 materials table ends at 1,000 F and recommended not to be used for all materials above 800 F except A352 LC2. Again Class 1500 @ 1,000F 430 psi.
3. Group 1.3 materials table ends at 1,000 F and recommended not to be used for all materials above 875 F. Again Class 1500 @ 1,000F 430 psi.
4. Group 1.4 materials table ends at 1,000 F and recommended not to be used for all materials above 800 F. Again Class 1500 @ 1,000F 430 psi.
5. Group 1.5 materials table ends at 1,000 F and recommended not to be used for all materials above 875 F. Class 900 @ 1,000F 495 psi.
6. Group 1.7 materials table ends at 1,050 F and recommended not to be used for all materials above 1,000 F. Class 900 @ 1,050F 475 psi.
7. Group 1.9 materials ( 1 1/4% Cr - 1/2% Mo) table ends at 1,200 F and recommended not to be used for all materials above 1,100 F. Class 1500 @ 1,100F 480 psi. That is material group which can be used for 1,100F @ 350 psi conditions.
8. Group 1.10 materials ( 2 1/4% Cr - 1% Mo) table ends at 1,200 F and recommended not to be used for all materials above 1,100 F. Class 1500 @ 1,100F 550 psi. That is material group which can be used for 1,100F @ 350 psi conditions.

If CS material means Carbon Steel, and forged flanges made of A105N, its limit is 800F. For 1,100 F operational temperatures you have to chose A182 Gr. F11 CL2 ( 1 1/4% Cr - 1/2% Mo) or A182 Gr. F22 CL3 ( 2 1/4% Cr - 1% Mo) forged steel flanges. These are permissible but not recommended to use above temperatures 1,100 F.

I think, wrong flange and stud material was used for this 10" line operating at 1,100 F. We don't know yet, what casting material were used for valves, and what pressure class was used anything below Class 1500 wouldn't work either.

Thanks,
Curtis

 

[MJCronin]

Exactly Curtis .... We still have no idea about the Flange Style or Class!!!

Looks like the original poster has abandoned this thread .....

MJCronin
Sr. Process Engineer