Hold Point, Witness Point and Review Point: How to Build an ITP for Tower Internals
An Inspection and Test Plan, or ITP, is not simply a list of tests.
It defines:
what will be checked, when it will be checked, who must be notified, what evidence is created, and whether production may continue.
For custom tower internals, a well-designed ITP can prevent important inspection opportunities from being missed.
Start with the Manufacturing Sequence
The ITP should follow the actual production process.
Depending on the product, stages may include:
- raw-material receipt;
- cutting;
- forming;
- welding;
- assembly;
- dimensional inspection;
- PMI;
- NDT;
- water testing;
- trial assembly;
- packing;
- final release.
Inspection points should occur when the characteristic is still accessible.
What Is a Hold Point?
A hold point means work cannot proceed beyond that stage until the specified approval or release occurs.
Example:
Material identification hold point before cutting specialty alloy plate.
If the purchaser or inspector does not release the hold point, production must stop.
Hold points should therefore be used selectively.
Too many can create unnecessary schedule delays.
What Is a Witness Point?
At a witness point, the purchaser or third-party inspector is invited to observe the activity.
If the inspector has been properly notified but does not attend, the supplier may often proceed according to the agreed procedure.
The exact rule should be stated in the ITP.
What Is a Review Point?
A review point typically involves reviewing:
- certificate;
- report;
- procedure;
- record.
Physical attendance may not be required.
Examples include:
review of MTC or dimensional inspection report.
Surveillance
Some projects also use surveillance activities where the inspector may observe work without requiring a formal stop or invitation for every unit.
This can be useful on large repetitive production runs.
Match Inspection Intensity to Risk
A standard PP random packing order does not need the same ITP as a large SS316L multi-internal EPC package.
Inspection level should reflect:
- process criticality;
- material risk;
- fabrication complexity;
- project specification.
Define Acceptance Criteria
Every ITP line should point to an acceptance basis:
- drawing;
- specification;
- standard;
- approved procedure.
Writing “dimension inspection” without saying what dimensions are acceptable provides limited value.
Define Responsibility
The ITP may identify roles such as:
- supplier QC;
- purchaser;
- EPC;
- TPI;
- end user.
Each party's involvement should be clear.
Define Records
Inspection should generate evidence.
Possible records include:
- MTC;
- PMI report;
- dimensional report;
- NDT report;
- water-test report;
- trial-assembly report;
- final inspection release.
These later become part of the MDR.
Notification Period
For witness and hold points, define how much advance notice the supplier must provide.
International projects may need enough time for:
travel or third-party scheduling.
Close the ITP
At project completion, the supplier should be able to show that each required inspection step was:
performed, waived, witnessed, reviewed, or otherwise formally closed.
Engineering Takeaway
A useful ITP follows the manufacturing sequence and applies the correct level of control at the moment the quality characteristic can actually be verified.
Hold, witness, review, and surveillance points should be selected deliberately rather than added as generic project terminology.