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BHA Inspection Criteria
15 November 2006
I am looking for some advice on tubular inspection criteria as
defined by T H Hill.

Our rig contract states that the drill collars shall be fully
inspected to meet the requirements of T H Hill DS-1 Category 4 (or

Within TH Hill Drill Stem Inspection manual, it refers to the
definition of Category 4 as ”œdrilling conditions more difficult than
Category 3. Significant fishing costs or losing part of the hole are
likely in the event of drill string failure”.

Further within the document it discusses setting acceptance criteria
for drill collars by specifying the acceptable bending strength
ratio range which establishes the dimensional requirements for drill
collar OD and ID and states a range for the size of drill collar.
There is also a reference to recommended inspection programs in
Table 2.3 (Component 3-5) for DC & HWDP.

The rig we are about to contract has 6.1/2” drill collars, which
have 4.1/2” IF connections. These used to be 4” IF but were recut to
4.1/2” IF.

The attached Tuboscope inspection sheet for the 6.1/2" drill collars
on the rig show the ODs and IDs, and the equivalent Bending Strength
Ratio. This shows that the BSR would be lower than the 2.25 - 2.75
(guideline within T H Hill) if the drill collars had 4.1/2” IF

This rig was working prior to our contract with 4.1/2” IF

We are being told that the threads on these drill collars would have
to be recut to 4” IF to meet the BSR as defined by the T H Hill
inspection criteria range.

We would like to keep the threads as 4.1/2” IF.

Has anyone had experience of this?
What is the potential impact or risk exposure by keeping 4.1/2" IF
connections with BSR as low as 1.80.

Tony Williams
5 answer(s)
QA/QC Engineer[Drilling , Completions and Intervention Tools)
Applus Veloci
Total Posts: 8
Join Date: 10/05/19

I know that I am replying to an old post but I hope It would still help someone in the forum.

In connection with very low BSR you can expect premature box connection failures and if it is very high pin end failure.

A solution to keep the NC-50 connection on the same tube by adding material to box end or by enlarging the ID of the pin connection end.

People can choose any of the above by considering the economic point of view.
As we look from the failure investigation point of better to go for the first method because we know the ID wear will be very gradual compared to OD reduction.

Lajeesh V G

Note from moderator:  I hope that regular users don't mind Lajeesh responding to this original post.  As most people know, Tony was a dear friend, and passed away some years ago.  His name still crops up, from time-to-time, and we all miss his boisterous laugh!  I hope that you are resting in peace, dear friend.

Drilling Consultant
SPREAD Associates
Total Posts: 9
Join Date: 11/07/06
Some years back whilst with Texaco we were drilling in Bulgaria. The
rig/well experienced many problems with washouts and connection
failures. We were using 4.1/2" IF, we swapped strings to 4" IF and
the problems magically stopped.
The drilling was hard; you can still get away with the 4.1/2" if you
have fairly benign drilling conditions.

Mike Willis
Consultant [retired Shell staff]
SPREAD Associates
Total Posts: 271
Join Date: 02/09/05
1994 Wk18 Zaterdag: Any faulty merchandise will be cheerfully
replaced with merchandise of equal quality”¦

Guide for evaluating Drill Collar OD, ID and connection
combinations, Bending Strength Ratio API RP 7G BSR 2.5

Dislike to see a reference to 4 1/2 IF made obsolete as far back as
March 1973.

Hope we are dealing with genuine API NC50 connections.

Facing with a weak BSR what can we do?

- Ensure we indeed have a NC 50 connection - proper thread profile,
stress relief features, bench mark etc.

- On eventual thread recut consider improving it :
SPE 18704 Improvement of DC fatigue by LET height reduction of pin.

REPRINT: III Congres Europeen d´ equipment petrolier The VDW Tool
joint thread (van der Wissel) ´59. T. Altmann Wirth Erkelenz,
Germany. [My Preference]

- External relief grooves [External relief grooves > 5,500,000
cycles; API IF mod 393,000 cy; API IF 240,000 cycles]

Managing Director -Relentless Pursuit of Perfection Ltd.
Relentless Pursuit Of Perfection Ltd.
Total Posts: 25
Join Date: 10/01/05
Hi Tony,

I have forwarded your email to Ray Procter of OCTG-Procter, a UK-
based consultancy, that specialise in this.

Please bear in mind that OCTG-Procter makes their living from this
knowledge so may be unabel to answer in the public domain.

Contact details are : and Tel : 44-1224 748602.

I hope this helps ..

Best wishes
Dave Taylor

Odfjell Drilling (Norway)
Odfjell Drilling
Total Posts: 7
Join Date: 28/07/06

We always inspect our BHA ea HWDP, DC subs to DS 1 cat 3-5 and DP to
DS 1 cat 4. This is normal practise in that range. Any inspection
co. Would tell you of BSR what acceptable.

Stig Larsen
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