An ITP that is agreed after manufacture has started is a record of what happened. An ITP agreed before the order is a plan, and it is the only mechanism that gives you control over the process.
The four intervention levels
H - Hold point. Work stops. It does not continue until the nominated party has attended or released the point in writing. This is the strongest control and it costs schedule if notification and attendance are not managed well.
W - Witness point. The nominated party is notified and may attend. If they do not attend within the agreed notice period, work continues. Most of an ITP is witness points.
R - Review. Document review only, no attendance. Used for records that can be assessed after the fact - certificates, charts, reports.
M - Monitor. In-process check performed by the manufacturer and recorded, with no external attendance.
Each row of the ITP carries a level for each party: manufacturer, third-party inspector, and client. They are frequently different - a point can be a hold for the TPI and a review for the client.
A representative ITP structure
| # | Activity | Acceptance basis | Mfr | TPI | Client |
|---|---|---|---|---|---|
| 1 | Review of GA drawing | Approved drawing | H | R | H |
| 2 | Forging mill certificate review | EN 10204 3.1, project spec | H | R | R |
| 3 | Forging heat treatment charts | Qualified cycle | H | R | R |
| 4 | Forging UT before machining | Project NDE spec | H | W | R |
| 5 | In-process dimensional check | GA drawing | M | - | - |
| 6 | Welding procedure review (WPS/PQR) | ASME Section IX | H | R | R |
| 7 | Hardfacing deposition | Qualified procedure | M | W | - |
| 8 | PWHT charts | Qualified cycle | H | R | R |
| 9 | Hardness survey after PWHT | Project spec range | H | W | R |
| 10 | PT on finished overlay | ASME Section V | H | W | - |
| 11 | PMI, all pressure parts | Project spec | H | W | R |
| 12 | Assembly, preload and clearances | Mfr procedure | M | - | - |
| 13 | Hydrostatic shell test | API 598 | H | H | W |
| 14 | Seat and back seat test | API 598 | H | H | W |
| 15 | Final dimensional inspection | GA drawing | H | W | R |
| 16 | Marking and nameplate | MSS SP-25 | H | W | - |
| 17 | Preservation and packing | Project spec | H | W | - |
| 18 | Document package review | Purchase order | H | H | H |
| 19 | Release note | - | H | H | H |
This is a starting structure, not a standard. Yours will differ, and it should - the point of the exercise is to agree what matters on your order.
How to use it
Send your ITP with the enquiry, not with the order. We mark it up: what we accept as written, what we accept subject to clarification, and what we cannot meet. The third category is short and it is the one worth reading. Discovering it after the order is placed costs schedule.
Be realistic about hold points. Every hold point is a place where the job stops until someone travels. Five well-chosen hold points give better control than twenty that get released by email because nobody could attend. The tests at rows 13 and 14 are the ones most worth holding.
Agree the notification period. Typically 10-15 working days for a witness point. It has to be long enough for travel and short enough not to build slack into every stage. State it on the ITP, not in an email.
Decide what happens when a point is missed. If the TPI does not attend a witness point within the notice period, does work continue? Usually yes, that is what distinguishes witness from hold. Write it down anyway.
What you get back
The signed-off ITP is part of the document package, with each row initialled and dated, and the corresponding record cross-referenced. It should be possible to pick any row and find the report that satisfies it.
If an ITP comes back with rows signed and no corresponding records, the ITP was administration rather than inspection.