Field Construction Tolerances 1

[DGrayPPD]

Okay, so we have a new situation that I have no experience with and need some wisdom/advice. It will be a little difficult to explain but I will try my best.

In regards to construction tolerances for piping...

We designed a fire water system composed of the storage tank, pump house, and all piping. We tied in to two points on the water main. A survey was done on those points for us to use in our design. The design was completed a few months back and we have issued the approval and bid packages for the project. All bulk material has been purchased based off the IFB package. Now comes the issue that I am not sure how to handle.

The storage tank has been erected and hydrotested, and the pump house has also been set. The client sent us drawings this morning of a survey that was done on all the nozzles of the tank post hydro and of the pump house. There were also various TOC points noted on the drawings. None of the nozzles and equipment is exactly where we told them to put it, which I expect as nothing is ever perfect. However, the tank was set 4" closer to the pump house than what it was supposed to be and none of the nozzles post construction are rotated and set exactly where they were during our design. Some are off 3/16" N or E, others up to 1 3/16".

Now, our PM is wanting to go back and change all the drawings to match the survey data. We have never received as-built survey points on equipment like this before. My questions are as follows:

1) What is the proper procedure? Should our packages be updated to reflect errors made during construction?
2) If our package is left alone and there are spools that have to be cut in the field, who is responsible to the contractor for the extra work? How does the extra work get communicated?
3) Our PM wants to update the Isos to show all coordinate changes and to change dimensions but does not want to update the model. Is this a bad idea? Seems like a bad practice to me. The client wants an as-built model and the PM does not think the coordinate accuracy in the model is important.

I understand that nothing is ever constructed perfect to a computer model, but when it is off this much, I just do not know the proper course of action to take. Thank you for any help I can get.

 

[Gator]

Design to 1/16", fab to 1/8", install to 1/4".

Can you trust the field measurements of the tank and the pumphouse?

Why does the PM want "to go back and change all the drawings to match the survey data" but not update the 3D model? S/he furthermore wants to just modify the isos auto-generated from the model? That's a very bad idea, in my opinion.

Are field fit welds included on the isos that could accommodate the discrepancies? What does the contract say about any required "field adjustments"?

 

[dik]

Is there one General Contractor involved? or is it a group of sub-contractors working for you/owner? Who is responsible for overall coordination?

Can it be handled as an 'As Built' condition with the contractor making a redline markup? Do you have an obligation to do 'As Built' drawings?

Dik

 

[DGrayPPD]

To Gator:

PM believes our drawings should match the as-built survey data. He does not think that updating the model is necessary because it would take too much time and the client only wants an as-built model of the site and will not be using it for future installations to tie into. It is very flawed thinking in my opinion. And there were field fit welds with an extra 6" included for most vertical piping to accommodate the differential settlement, but most N-S and E-W piping was only supplied with field welds which do not contain any extra piping.

To dik:

The client is using a few different sub-contractors. I am not sure who is responsible for overall coordination. As far as I am aware, we are will issue an as-built 3D model but that is all.

 

[DGrayPPD]

To me it just sounds like the contractor did a poor job locating and constructing the equipment and our firm should not have to go back and make changes to our design and drawings to accommodate the errors.

 

[dik]

In these environs, the owner would be considered as the Constructor and would be responsible for all health and safety issues as well as other things. An advantage of having a General Contractor. Since the owner is looking after things, what is his suggestion on how to fix? and who is responsible?

He can pay you for making changes.

Are you being paid to produce 'As Built' drawings... if not, then, I would not be changing the documents. For unpaid work reasons as well liability.

Dik

 

[DGrayPPD]

Again, I am kind of the low man on the totem pole and not kept in the loop as much as I should be no matter how much I express that I should be involved, being the one designing the facility, but that is a discussion for another day, but I do not think that we are producing as-built drawings so my thinking matches what you are saying. I do not think we should be changing drawings.

 

[Gator]

So the client wants an as-built model but not as-built drawings? Ideally both should match, but I'd choose competently measured (and signed-off) as-built drawings over an as-built model.

 

[DGrayPPD]

I agree. Nothing about this project or client has made sense to me yet.

 

[pennpiper]

DGray.
Based on your original posting and your follow-up comments I come up with the following:
a) The Client is his own Prime Contractor
b) Your Company (Piping) and all other parties (Surveying, Civil/Foundations, Tank Fab & Erection, Pump Installation, Electrical, Instrumentation, Painting, etc) are Sub-Contractors.
c) Your Company is only responsible for what is in the Piping Sub-Contract.
d) Go back and read the Contract.

Sometimes its possible to do all the right things and still get bad results

 

[mk3223]

It should have the "field welds" assigned for the construction to adjust the discrepancies between the design and the fabrication. It relies on the piping contractor to adjust the piping spools to fit. Of course, you want to record all the changes as well as the hours for the extra work performed for the contract dispute in the future, as required.
Looking into the way to save cost as well as complete the work as necessary, so it is to be a win-win for both owner and contractors.

 

[DGrayPPD]

Thank you for all your help.

 

[DekDee]

Let's just forget about the model for the moment.
Unless you do things differently on the other side of the world the model is nothing more than a fabrication, construction, installation tool.
The model is not entered into the MDR which contains all the critical quality documentation.
Approved Isometrics and As-Built Isometrics are the only records of what was actually designed and what was actually built.

If the contractor put nozzles in where they wanted and not where the designer wanted it should have been an NCR.
Seems like you are chasing your tail here.

You designed it - end of story.
If the contractor built it differently then the arguement is between the Client and the Contractor to resolve, not the designer.
Regards,
Shane

 

[dik]

Shane: Yup... your last two paragraphs really sums it up.

Dik