Spring Supports Revamp at Ammonia Plant

[uzair.farooq]

I am given a project on Revamp of Spring Supports at an Ammonia Plant where I work as a Maintenance Engineer. We are facing serious issues during the project, and hence I need guidance from experienced persons in the field.
Briefly described, our plant was relocated from a place where it was in operation for almost 20 years before it was mothballed. Since its relocation, the plant has been in operation for 20 years. The plant, and hence the spring supports, are in service for almost 40 years. The supports are mostly installed on services having pressures greater than 1500 psi and temperatures higher than 400 F.

We have planned to execute the project in the following phases:

1. Carry out audit of the existing facility and identify the spring support conditions.
2. Identify the faulty supports and take corrective action.
3. Develop Preventive Maintenance (PM) plans for the supports.

For this I need guidance on following:

1. For the audit, we are visually inspecting the supports to see whether the springs are over or under loaded, conditions of supports, conditions of locking nuts and signs of corrosion. Can we add any thing else that can increase our understanding of the current condition?

2a. Does anyone has any experience of repairing the spring supports?
2b. Are there any vendors which offer cheaper solutions for repair / reclamation of supports?
2c. Can we purchase any used spring supports which are in a better conditions? If so, where to look for them?
2d. Can we replace a spring supports on-line? i.e. while the line is in service?
2e. What are the codes and standards which govern the installation / maintenance of supports?

3a. Are there any standards which guide about PM plan for supports?
3b. Does anyone has any experience in this regard?

Thank you for being patient and for any advice that you can give. :-)

Regards,

 

[Danger]

Welcome to PF, Uzair.farook.
I have so little knowledge in this field that I'm not even sure what you're talking about. That's never stopped me from expressing an opinion before, however, so here goes:
I'm just wondering why you are restricting your inspection to a visual one, since it seems to be something pretty important. Do you not have access to portable diagnostic equipment such as X-ray or magnaflux machines? My apologies if the question is out of line.

 

[Pkruse]

I've worked a great deal in industrial maintenance, but I'm not sure what you mean by spring supports. Several possibilities come to mind. Care to post a picture?

 

[uzair.farooq]

I have attached a picture of the spring support (also called spring hanger) for clarity.

@Danger: As far as I know there is no such practice for Non Destructive Examination of spring supports. Please share if you have any information about it.

 

[Pkruse]

I’ve worked with similar devices. The only troubles I’ve had with them in the long term are structural rust. Judging by these pictures, you don’t have that problem.

The purpose is to isolate the structure from vibrations, while at the same time selecting a spring rate that does not get happy at any of the modes produced by your equipment. If you are not having vibration problems, then the second objective is still satisfied. Since they are still compressed about the same as they originally were, they still have the same spring rate. A simple visual inspection should be able to quickly detect any of these three problems: Rust, vibration, and spring rate.

Another test is also quick and cheap. The concern is that dirt, trash, and rust might bind the mechanism up such that it does not freely move up and down with changing loads. Clean them, lubricate them, and then put a hydraulic jack under the structure. If the spring moves as you relive its load with the jack, then the mechanism is still free to move and operate as designed.

These things should be on a regular maintenance program to keep them clean and lubricated. Depending on the operating environment, the frequency could be as short as a year or less, or as long as a decade.

 

[Danger]

@Danger: As far as I know there is no such practice for Non Destructive Examination of spring supports. Please share if you have any information about it.

Sorry, but I was serious when I said that I know nothing about it. My suggestion was just a casual thought. For one thing, it turns out that I misinterpreted your question. When you said "spring supports", I thought that you meant the structures that hold the springs, rather than the springs themselves. The closest experience that I have with anything like this was unlatching the suspension system of a phonograph turntable when removing it from the shipping box, and that was on a somewhat smaller scale than yours.
It seems that you are in very good hands with Pkruse, though; I herewith bow out of the discussion.

 

[Q_Goest]

Hi uzair. You may or may not be aware of exactly what those supports are doing. I've heard of spring loaded supports being used to help isolate a machine or other structures from vibration but I don't think that's what you have here. My opinion is these supports are only being used to support piping and accommodate thermal loads. Note that the piping you have is large, heavy and subject to fairly significant changes in temperature. You can tell from the insulation on the pipe and the discoloration that the pipes are subject to temperature swings. They expand when hot and contract again when cooling down. The supports can't be rigid or they would subject the pipe and pipe supports to stresses that are outside the range of the allowable stresses, possibly bending or breaking the supports or piping in the process. So the supports are in there to allow for movement of the piping due to the thermal expansion and contraction.

In the US we use ASME B31.xx piping codes to determine where piping supports can be located to keep the system within the stress limits set forth in the specification. For an ammonia plant, it would be designed per ASME B31.3. There should be documentation of this analysis and in that documentation the piping supports should be modeled. The supports are then going to have detailed drawings created including specifications for the piping supports. Those drawings and specifications for the supports can be used to purchase new supports if you need to replace them but they generally don't need much maintenance. I would suggest inspecting them for obvious damage, keeping them clean, making sure nothing drops into them that might hinder the spring's movement, and paint them occasionally if needed to inhibit corrosion.

There's a few web pages here that you might look over to get some additional information about this issue:
http://www.pipesupports.com/files/u2/Book_on_Spring_Hangers_rev_0.pdf
(see page 76 for maintenance)

http://www.gshangers.com/engsupport_cms.php