11
To:
Subject:
Drift test and Drift size
Question:
Can you supply a definition and dimensions for a
drift tool? What tolerance do they have?
Answer:
To get the definition for Drift,
Click here.
After you have read the definition, click on the
word Drift, it will take you to
Flange Make-up, Stand-off / No Stand-off and Drift between Flanges and
DRIFT TESTING OF
ASSEMBLED EQUIPMENT. There you will find a Utility that will allow you
to select a flange connection, and when you do it will produce the
API
drift minimum dimensions for full bore equipment. Observe that the
O.D.
of the drift always equals the nominal bore of the connection, minus
.031 inch. The length seems related to the bore for smaller sizes, but API provides no tolerance information, they only state these dimensions
as minimums.
API bores always have a plus .031 inch tolerance
over the nominal, with no minus tolerance allowed. Manufacturers
establish the tolerance ( above the minimum sizes required by API ) that
they want to live with for the drifts. As long as the drifts meet the
minimums and pass through the bores, the manufacturer has met the drift
requirement for that bore size.
Note that many well head components have bores
other than API full bores, and manufacturers usually follow the same
design pattern in the relationship of bore and drift size for these
other bores unless Operators make special requests.
In special cases Operators may know that their
well will require the insertion of special tools that will have special
O.D.s and lengths other than the API specified Drift requirement. These
Operators may specify a special Drift O.D. and length to manufacturers
and/or assemblers so as to assure that these tools will later pass
through the assembled equipment.
Click here for another related Q & A.
