Interpretation and measurement of flatness when specified in inch/feet or mm/meter 3

[vishnu_G]

We are in process of installing a turbine skid on metal frame which has 3 mounting pads. Each pad is about 1 meter x 0.5 meter size. Manufacturer has specified following requirements for the mounting pads. "Each foundation pad or Sole Plate should be installed flat within 0.030”/ft (2.5 mm/m) and coplanar to 0.120” (3.0 mm) to the other pads.
Manufacturer field rep. inspected pad and found that surface of pad is not flat as required 0.03"/feet. Construction contractor is arguing that it is flat as per 2.5mm/meter requirement specified in metric unit and imperial unit 0.030"/feet is not same as metric unit 2.5 mm/meter for flatness. Can any one provide more information on how to interpret flatness for rectangular pad specified in inch/feet or mm /meter and what is the best way to carry out field measurement? Is 0.030 in/ft (0.025 mm/cm) can be considered same as 0.030”/ft ([highlight #FCE94F]2.5 mm/m[/highlight]) for this purpose?

 

[Brainton]

occasionally palpable floor is specified to have a deviation 1/8 over 10 feet. This is measured by laying a 10 foot straightened on the finish floor that is a huge gap below the straightedge. this method is used for many years.

 

this method is used for many years.

But it is fading fast. Laser metrology is now easily available and is now the standard for any critical measurement. I would use straight edges only for quick and dirty in-process checks.



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

 

[MintJulep]

Numerically they are the same.

However because of the implied method of inspection they are not necessarily equivalent.

Fundamentally the requirement is incomplete and ambiguous.

https://www.tes-rnd.com/en/straightness-per-unit-length/

I guess that you have good cause to claim that because the manufacturer's specification is incomplete and ambiguous that they need to pay to bring the pads to the condition that satisfies them.

 

[IRstuff]

I think the contractor is bullcrapping; if both requirements are specified, then they need to meet BOTH. They obviously screwed up and are picking and choosing the units to pass.

Moreover, the primary units are imperial, metric is secondary; otherwise, they would have been written the other way around, i.e., the imperial units in parentheses. They can't hide behind essentially a typographical error to get a pass.

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[vishnu_G]

Thanks MintJulep and IRstuff for your valuable input. I agree that manufacturer should have specified requirement in more details at the same time we know that constructor is using metric data in parenthesis 2.5 mm/meter as an excuse only after issue is discovered and there is cost and schedule impact and it was never a root cause of the issue.

 

[DekDee]

What are the primary measurement units used for these plates ?
You have noted "Each pad is about 1 meter x 0.5 meter size."
Every American code/standard I am aware of has Customary Units first and metric in parenthesis.
The important thing is either can be used as long as that unit of measurement is used consistently - you cannot pick and choose.

 

I think the contractor is bullcrapping;

I normally take an extremely dim view of the current mania for pressing nouns into verb duty, but I feel for this example it is wholly appropriate.

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

 

[vishnu_G]

The statement "Each foundation pad or Sole Plate should be installed flat within 0.030”/ft (2.5 mm/m) and coplanar to 0.120” (3.0 mm) to the other pads." is verbatim from the manufacturer manual of the Turbine Generator skid who is American. Mounting pad dimensions mentioned by me in metric here is for information as in Canada we are used to metric. Construction contractor who is also American Company uses imperial dimension for most of their work ,but after rejection of mounting pad by the manufacturer field rep due to lack of the flatness which is affecting cost and schedule due to rework the interpretation of flatness requirement provided by the manufacture in parenthesis "(2.5mm/meter)" is used as a defense of the root cause of rework.

 

[ewh]

When specifying two value systems such as imperial/metric, one always has to be reference because, in absolute terms, they are not equal. They do not convert to clean numbers and there will always be trailing decimal places when a value is converted. For this reason they do not define the same part. If the imperial value is first the metric should always be in parenthesis, as it is reference. Reference dimensions are not supposed to be used for fabrication or inspection, and doing so is not a legitimate defense when parts are found out of spec.

edit: spelling correction

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