Drilling Jar Testing Procedure: Bench Test Steps, Acceptance Criteria, and Test Records

How a drilling jar tester verifies release values, stroke, and repeatability before dispatch: the bench test step by step, what the report records, and how to read failure signatures on the load curve.

A drilling jar tester is a bench system that pulls, compresses, and cycles a drilling or fishing jar under controlled load so the workshop can verify latch release values, stroke, and hydraulic response before the tool is dispatched to the rig. The test replaces guesswork with a recorded measurement: the jar either releases inside its specified window, or it goes back to the service bay.

Why Jars Are Tested Before Dispatch

A jar that fires late, fires early, or does not fire at all is not a small problem. By the time the failure shows up, the string is stuck, the rig is on standby, and the recovery operation costs more per day than the jar cost in total. Testing after every service interval — and before every dispatch — is how service centers keep that risk on the bench, where it is cheap.

The logic is the same one we apply across the workshop: if a parameter matters downhole, it gets measured and recorded on surface first.

The Bench Test, Step by Step

1. Identification and visual inspection

Confirm the serial number against the service record, check thread condition on both connections, and inspect for seal weep or impact damage. A jar with damaged threads does not go on the tester — it goes to make-and-break first.

2. Mounting and alignment

The jar is clamped between the fixed head and the traveling head of the tester. Alignment matters: a side load on the mandrel distorts release readings and can mark the tool. Modern benches use centering supports sized to the jar OD.

3. Tension (upward jarring) test

The tester applies a steadily increasing pull while the operator watches the live load trace. The reading of interest is the release point: the load at which the jar trips and delivers its impact stroke. That value is compared against the setting specified for the tool size and service class.

4. Compression (downward jarring) test

The same cycle in the opposite direction, for jars with a down-jarring function. Release value and stroke length are recorded separately from the tension figures.

5. Repeat cycles

A single clean release proves little. Typical acceptance requires several consecutive releases with results falling inside a tight band. Scatter between cycles is itself a finding — it usually points at internal seal or detent wear.

6. Recording and certificate

The tester logs load against time for every cycle. The curves go into the test certificate together with the release values, stroke measurements, operator, date, and the tester’s own calibration reference.

What the Test Report Records

Reading the Curve: Common Failure Signatures

Release value drifting upward across cycles usually means detent wear or incorrect re-setting after service. Early release under light load points at a worn latch. A sawtooth trace before release is stick-slip inside the tool — often contamination or a dry mandrel. Any of these on the bench is a cheap find; the same signature discovered downhole is a fishing job.

Where the Jar Tester Sits in the Workshop

In a full downhole tool service line the tester sits after disassembly, inspection, and re-assembly, and before final thread protection and dispatch. The workflow mirrors what we describe for motors on the drilling motor test stand: service the tool, then prove it, then ship it with the proof attached.

For the equipment itself — frame capacities, drive options, and instrumentation — see the Galip drilling jar tester page. For how drilling and fishing jars differ in function and test emphasis, the drilling jar vs fishing jar comparison covers both tools side by side.

Drilling Jar Testing FAQ

How often should a drilling jar be tested?

After every service interval and before every dispatch. Many operators also require a current test certificate dated within a set number of days of the tool arriving on location.

Can one tester handle both drilling jars and fishing jars?

Yes, provided the frame covers the required pull capacity and both tension and compression cycles. The test emphasis differs — fishing jars are cycled harder in tension — but the bench and instrumentation are the same.

What does a jar test certificate contain?

Tool identity and serial, release values per cycle in both directions, stroke measurement, the logged load-time curves, operator and date, and the calibration reference of the tester itself. That last line is what makes the certificate defensible in an audit.

Is a bench test a substitute for service?

No. The test proves the outcome of service; it does not replace it. A jar that fails on the bench goes back one station, not out the door.

Related: the bench test only proves the service work — for everything that comes before it, see the drilling jar maintenance checklist: 11 inspection points before testing.