Testing Tension Bolts 3

[SeanStructural]

The special inspector said that he has to test 5-bolts from every lot and that three of which ONLY has to pass.

These are A325 tension bolts.

The 60% passing seems very high to me. What do you think?

 

[CoryPad]

ASTM A325 refers to ASTM F1470 Standard Practice for Fastener Sampling for Specified Mechanical Properties and Performance Inspection
for lot inspection. ASTM F1470 states that five bolts are the correct number of samples to represent a lot of parts containing between 35 001 pieces and 150 000 pieces. All five samples must meet the requirements - any failure among the five pieces is cause for rejection of the entire lot.

 

[MJCronin]

Looks like that inspector is certainly "special".......

MJCronin
Sr. Process Engineer

 

[rb1957]

60% passing the spec minimum seems Really low to me

another day in paradise, or is paradise one day closer ?

 

[paddingtongreen]

It looks as though we have people at cross purposes here.

The OP is speaking of the inspection of installed bolts.

CoryPad is referring to factory tests that include physical and chemical properties.

Based on my experience, 60% is a low expectation, in a properly installed joint, I would not be surprised at 100%, much depends on the method of installation.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[SeanStructural]

To clarify, it is a job site not a manufacturing facility. The inspection is prior to installation once we receive the bolts on site.

 

[CoryPad]

SeanStructural,

You used the words test and inspection. What are these? It is unlikely that anything on the bolts that can be tested or inspected is allowed to to not meet the requirements.

 

[paddingtongreen]

CoryPad, They sometimes run a sample of twist-off bolts in a Skidmore. Then there are inspection tests with a calibrated torque wrench of a sample of installed bolts. Since in most of the connections the bolts are not in tension other than the installation tension, they don't all have to meet spec. If they were in tension as part of the function, they would have a different criteria, set by the EOR.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[SeanStructural]

In our case these are TC bolts and have to be inspected by the special inspector by testing a representative sample

The RCSC reads: "7.2. Required Testing:
A representative sample of not fewer than three complete fastener assemblies of each combination of diameter, length, grade and lot to be used in the work shall be checked at the site of installation in a tension calibrator to verify that the pretensioning method develops a pretension that is equal to or greater than that specified in Table 7.1."

It only requires three not five and it does not indicate the passing rate. Still the 60% is way too high.

 

[paddingtongreen]

SeanStructural, you indicate that these are to be installed on a Skidmore or other machine before they are approved for use in the structure. I didn't think anyone else did this, my boss and I started these in the early days when we were building a nuke and these bolts were new on the market, they weren't mentioned in the AISC Spec., we were ridiculed for doing it. We broke a higher proportion than you, on a Skidmore, but we had a much higher than 60% passing. If yours have been lying around for a while, long enough for the lubrication film to dissipate, then you might have problems from increased friction.

I pretty much became an expert on bolted connections because of the research involved, but that was long ago and I'm probably way behind now. I just counted, it was about 40 years ago.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[SeanStructural]

paddingtongreen - When did I mention a Skidmore?

 

[paddingtongreen]

You said, "In our case these are TC bolts and have to be inspected by the special inspector by testing a representative sample"

The only way I know to do this is to install them on a machine that measures the tension. I mentioned a Skidmore, the usual machine, or other machine. It was simply my interpretation of the requirement. You included a section of the RCSC that calls for a calibrator, again, I assumed a Skidmore or equal. I don't know how else to do it.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[wannabeSE]

Sean,
The RCSC says to test not fewer than 3 bolts and if any fail the tension test, then the cause must be determined and resolved before they are used for work.

 

[DekDee]

If it is a "representative sample" then of course it must be 100% pass rate.
Otherwise, what is the point of doing the test ?
Cheers,
DD

 

[69Firebird]

3 from each lot and they must all break above the minimum. The skid more is the only way I am aware of testing, altho there may be other means

 

[chicopee]

Seanstructural, what type of a job site is it?

 

[JIPMKWA]

SeanStructural - I am an ICC certified special inspector and have had to do this a few times. All you are testing is that the "Fastener assembly" be it a bolt/washer/nut or bolt/nut or bolt/direct tension indicator washer/nut or T.C bolt all work together as an "Assembly" to achieve the required pretension for your size/grade bolt.

When you put them in a skidmore ( calibrated tension checking device ) you are doing what is called " Pre installation verification " which is a 5% higher tension than what it would be up on the steel.

We'll use a 7/8" A325 bolt for example.

The required pretension for this particular bolt is 39 Kips. When you do the Pre-Installation verification you test it to 41 Kips. If this bolt snaps , like someone said before , there is an issue. You then grab 3 more bolts from that lot and try again - If they break again that particular lot of bolts is rejected.


Hope that helps and I am not sure where he came up with 5 bolts.