orer China junk.....

TITLE: Defective Bolting Materials
CONCERN/ISSUE/RISK:
There have been two recent instances where defective stud bolts have been discovered at two sites in North
America - Dow Chemicals facility at Sarnia, Ontario, and the Valero refinery in Louisiana. It is believed these
two instances happened in the past two months
The bolts originated in China and as such, there is a concern that similar stud bolts from the same source
could be present in BG assets and that their presence could affect maintenance procedures and impact asset
integrity.
CIRCUMSTANCES:
From the information available the situation at the Dow facility:
* Three PTFE coated stud bolts failed during bolt-up during make-up of flanged joints - two failed during
tightening with a hand wrench, one failed during tightening with a torque wrench
* The stud bolts were supplied to ASTM A193 B7 with "SUN" stamped on the end. It is understood this
represents Sun Fasteners in Ningbo, China as the manufacturer (see Fig 1)
* The failed studs were all ¾" x 4¾". Other sizes from the same supplier gave no apparent problem
* Cross sectioning of the failed bolts showed transverse voids along the bolt shank (see Fig 2)
* One of the failed stud bolts was tested and broke at a torque of 40ftlb (54Nm) - see Fig 3 Further
investigation on other studs indicated that it could be torque tightened to 150ftlb (203Nm) before failure
* An ultrasonic testing technique was developed to inspect installed bolts to check for similar internal
flaws
* All bolts from this supplier will be replaced and future bolts no longer purchased from this supplier
There are no details available for the Valero incident but it is believed the defective stud bolt was found during
inspection following notification of the incident at Dow.
Other operators in North America have been made aware of these two instances
INVESTIGATION:
Stud bolts supplied to ASTM A193 B7 may be cold drawn, and then threaded before or after any heat
treatment. The manufacturing procedure is not known for the bolts in question and no formal investigation has
been conducted into the reason for the flaws but it is possible that these were induced during an improper cold
drawing process that may also be associated with less than optimal steel making technology.
The extent of testing for these bolts is limited to one tension test per 1500lb (780kg) lot size and as such there
is only limited scope to detect defective studs by mechanical testing.
If poor drawing techniques were a contributory factor, this may lead to excessive hardness above the ASTM
limit and this would be one method of checking for potentially defective components - any such testing would
need to be validated with a procedure qualification using representative materials and hardness testers.
Details of the specific ultrasonic technique mentioned above are not known but it is expected that this would
be a conventional pulse echo technique using specifically designed probes - it is expected that most
reputable NDE companies should be able to perform this service
A torque of 150ftlb is typical for this size of bolt with a high coefficient of friction lubricant and if stud bolts with
these types of flaw have been installed but the gasket has been successfully seated during the initial pre-load
and the flange joint has been operating without leaks allowing for any bolt relaxation, there is probably no
immediate 'risk' that the bolts will fail and cause a release. However, if the bolt is subject to fatigue or to low
temperatures there is an increased risk of failure and this should be taken into account in assessing any
remedial action.
RECOMMENDATIONS:
To minimise potential risks to long term asset integrity, the following actions are recommended:
* Conduct an audit of each asset's procurement policy to confirm whether any stud bolts have been
supplied by Sun Fasteners (all sizes and types, not just ¾" x 4¾" PTFE coated stud bolts). This should
include not only an asset's direct procurement stock but bolts supplied as part of equipment, packages
etc.
* If audit identifies that stud bolts have been supplied from this supplier but not installed, quarantine any
bolts in the stores - in principle, stud bolts from Sun Fasteners should not be used for any new work.
Where such bolts have been installed but the flange joint has not been commissioned, hold executing
further work until a risk assessment is performed in line with that for live plant
* If audit identifies that stud bolts have been supplied from this supplier and installed in live plant, carry
out an assessment of the criticality of each system/equipment item/package where such bolts have
been installed to determine a 'risk' ranking for further in-situ inspection and evaluation - hydrocarbon
and toxic service should be highest priority, studs on non hydrocarbon service should be ranked against
pressure
* Once a ranking has been established, develop an inspection plan to check each flanged joint in the
system/equipment item/package. Where a joint is found with one or more bolts from this supplier but
the joint is sound, a risk assessment should be made whether to leave the flange as-is and replace stud
bolts at next planned shutdown or undertake in-situ replacement
* Where in-situ replacement is undertaken, this shall only be done in full accordance with the
requirements of BGA-ENG-MECH-TS-0012 and OMS Guideline G5011. Note, that wherever possible,
system should be de-pressurised before undertaking any replacement - where ¾" x 4¾" bolts are
present in 4-hole flanges, hot bolting will not normally be permitted although odd bolting may
* Ensure that all contractors working for an asset are aware of this problem and remedial actions
proposed - this will include engineering contractors, flange management contractors and any other third
party carrying out procurement on the asset's behalf