srp f91.pdf
TRANSCRIPT
SRP‟s Experience with P91 Piping
Mike Rutledge
August 10, 2009
John Alice, Metallurgist
SRP (Salt River Project)
Supplier of Water & Power to Phoenix, AZ
Summer Load 2009, ~6500 MW
Resource Mix with P91:
1 Coal Plant, 400MW (scheduled to go commercial Dec. „09)
3 Combined Cycle Plants Desert Basin, 2X1, 600 MW
Kyrene, 1X1, 250 MW
Santan, 2X1 & 1X1, 860 MW
Inspection LocationsShop and Field weldsFittingsTerminal points such as header
connections, valve connections, turbine connectionsDissimilar metal welds (P91 to P22 and
Cr-Mo-V) Areas of personnel trafficAs part of our HEP Inspection Program
Inspection Methods for P91
Wet Fluorescent Magnetic Particle
Shear wave ultrasonics and radiography of
indications
Hardness
Surface replication at dissimilar metal
welds (DMW‟s) and „soft areas‟
First P91 Inspection at SRP -
Desert Basin in March 2006
Desert Basin began operation in 2001
SRP purchased in 2003 from Reliant
2 SW 501FD2 CT‟s
2 NEM HRSG‟s
1 GE steam turbine
AE – Black and Veatch/Zachary
March 2006
Main steam induction bend and reducer leading into north CMSV was unusually soft (140‟s HB).
March 2006 Summary
Three MS induction bends - soft
One MS reducer -soft
Four sections of HRH pipe - soft
October 2006
Replaced north soft main steam bend. (Rechecked north main steam induction
bend during the Summer of 2006. Found no change.)
Rechecked the south main steam bend. Confirmed still acceptable.
Checked more main steam induction bends & other P91 pipe.
October 2006
Found two more soft main steam induction bends (140‟s HB).
October 2006
Found four sections of hot reheat pipe to be soft
(150‟s HB)
April 2007
◦ HRH induction bend had mid-span soft areas
◦ HRH induction bend low hardness at welds One of these welds had 3 -1” long linear indications
Ultimately determined to have significant subsurface depth
Welds ground out and redone
March 2008
The section of pipe upstream of the Unit 1 main isolation valve was “soft”, including the drip leg.
March 2008
The pressure equalization valves (F22) connected to the main steam isolation valve (C12A)
contained stainless steel piping and fittings (316/316L), which is undesirable in cycling service.
March 2008
These two soft main steam induction bends found during the October 2006 inspection were replaced.
October 2008
Three hard welds (>300HB) were found in the 10” diameter piping leading into the HP steam turbine bypass valves. They were PWHT‟d to reduce the hardness to <280HB.
October 2008
Cracks were found at the toe of the saddle
weld connecting the trunnion to the main
steam pipe all around the weld on the pipe
side. This condition was found at both units.
October 2008
One soft MS induction bend was found, about
140-180 HB.
October 2008
Damage caused by alignment/
fit-up lugs.
October 2008
A section of small diameter pipe that appeared to serve no purpose was found. In addition, it was P22 and
determined to have inadequate wall thickness. It was removed. The penetrations were replaced with RT plugs.
HP bypass valve
HOT REHEAT
MAIN ISOLATION
VALVE LEAK
The crack was at
the 6 o‟clock
position and
extended from the
weld into the base
metal of the
pressure equalizer
piping.
November 2008
Kyrene Unit 7 in May 2006
K7 began operation in late 2002
1 GE 7FA+e CT
1 Alstom HRSG
1 GE steam turbine
AE – Stanley Consultants
TIC – on site welding
May 2006
Four small elbows at the outlet of the HP
Superheat were soft (140‟s HB).
400X
May 2006
Hot reheat transition
piece from Alstom
(P22) to Stanley
(P91) was seam
welded P91.
B9-DMW
May 2006
A reducer, pup piece and elbow of the main steam piping was soft (140‟s HB).
400X
May 2006
Main steam transition piece welded to
MSSV was seam welded P91.
400X
May 2006
Cracked 18”x14” weldolet of the hot reheat system. Mechanism was creep cavitation in the Type IV zone.
May 2007
HP Steam Bypass Valve
P22 P91
Outlet Weld is a B9 DMW (P91-P22)
May 2007
HP Steam Bypass Valve
Internal videoprobe inspection of outlet weld revealed thermal
fatigue cracks along the downstream weld toe.
Downstream-P22
Downstream-P22
October 2007
HP Steam Bypass Valve
Outlet weld
Outlet Weld is a B9 DMW (P91-P22)
Flow
P22 P91
October 2007
HP Steam Bypass Valve -replacedUpstream counterbore-P91
Downstream-P22
Internal videoprobe inspection of
outlet weld revealed thermal
fatigue cracks along counterbore
and weld toe.
October 2007
HP Steam Bypass Valve -replaced
Mounted section from 12 o’clock
position
Mounted section from 6 o’clock
position
October 2007
Hot Reheat “Transition Piece” Piping
HRSG P22 pipe
B9-DMWThe plate was
verified to be
Grade 91
material, but
the weld metal
was straight
9Cr – 1Mo (no
V or Nb).
October 2007
Main Steam “Transition Piece” Piping
The plate was
verified to be
Grade 91
material, but
the weld metal
was straight
9Cr – 1Mo (no
V or Nb).
February 2007
Hot Reheat Steam Bypass Valve
February 2007
Hot Reheat Steam Bypass Valve
Santan Units in December 2006
Santan new units began operation in
2005.
3 GE 7FA+e CT‟s
3 Alstom HRSG‟s
2 GE steam turbine
AE - Sargent & Lundy
December 2006
High Press Superheat – one tee soft only on west side, three elbows marginally soft.
December 2006
Reheat Steam – two center tees soft.
400X
December 2006
Two main steam elbows soft.
Elbow microstructure, 400X
December 2006
One weld soft on one side suggests problems during PWHT.
October 2007
◦ 4 MS fittings;
1 elbow, 2 tees, 1 reducer - soft
◦ MS Flow element leak.
DMW issue.
Repaired and ultimately replaced.
October 2007
Unit 5A flow element
September 2007
The discolored (overcooked) fitting just below the HP turbine shell was found to be hard, which suggests it
was heated to above the lower critical temperature during postweld heat treatment.
September 2007
316HSS
Inconel weld
Inconel weld
P91
P91
The flow element consists of an unusual combination of materials, that is, P91 welded
to 316HSS using Inconel filler.
September 2007
The LP steam bypass valve outlet weld showed some erosion from the attemperator spray and
some crack – like linear indications along the counterbore and upstream weld toe.
September 2007
The hot reheat steam bypass valve was replaced because of thermal
fatigue cracking in the outlet weld.
May 2008
◦ HP/MS; 2 spool pieces, 2 elbows, 1 tee – soft
May 2008
P91
P91P91Inconel Inconel
316SS
Main steam flow element
(316SS) joined to P91 with
Inconel.
May 2008
HR Bypass Valve
Crack on the OD at the
weld toe
May 2008
HR Bypass Valve Samples
April 2008
The non-return valves are large castings and were found to
have low hardness, less than 170HB. The microstructure is
not typical of a casting.
Typical microstructure, 400X
April 2008
The two short pup pieces just downstream of
the non-return valve at Unit 5A were very soft,
on the east side. The microstructure
consisted of ferrite and carbides.
Typical microstructure, 400X
April 2008
The hardness of the stop valves was non-uniform
and ranged from 150 – 210HB. The microstructure
exhibited undesirable features, including some
delta ferrite.
Typical microstructure, 400X
April 2008
The main steam elbows at Unit 5B
between welds W5 and W6 and welds W9
and W10 were soft, less than 160HB, on
the north side only. Their
microstructures were consistent with
degraded material.
For the common piping leading to the
turbine, the large tee between welds W12
and W13 was found to be soft, less than
175HB, on the east side only.
SRP Outage Summaries
2006-2009 11 Outages
68 Findings (soft, weld metal issue, crack, etc.)
16 Repair/Replace Actions Needed
AVERAGES
◦ +6 Findings per Outage
◦ ~1.5 Repair/Replace Actions Needed
Unresolved Issues Hardness Testing – suitable devices, surface prep, what
locations, how many readings ?? Some kind of protocol is needed. What do we do with components with marginal hardness ? Soft areas ??
Surface replication good enough ?? different methods or techniques?
Scoop samples ? Boat samples ? Devices ??
What is the expected lives of anomalous microstructures ?
What properties do we assume for expected life estimates ??
Should we hold the piping suppliers responsible for the replacement of soft pipe ?? Or, should we require them to prove that the component is fit for long term service by analysis ??
Etc.
Specific Concerns
Fittings such as, elbows, tees, wyes, laterals, and reducers may not be heat treated properly and may not meet the ASME/ASTM requirements. There are no Code Police.
Welds can be pwht‟d improperly.
Large Weld-o-let‟s can be susceptible to Type IV cracking.
ASTM‟s do not have any minimum hardness limits. Codes are not enough!
Spool piece drawings needed to locate shop welds and any seam welded fittings...these are sometimes hard to come by.
Steam turbine bypass valves are particularly vulnerable to thermal fatigue cracking. Retrofitting with a liner is required for reliable operation.
Etc.
Actions
P91 requires close surveillance during all phases of fabrication and construction to avoid problems. QC of all new materials is critical. Don‟t trust the supplier.
Component suppliers and fabricators must themselves possess, or must have access to detailed metallurgical expertise and experience to deal effectively with these materials.
Anomalous microstructures can be very difficult to interpret. Atlas of microstructures is needed and correlated with hardness.
Detailed purchasing specifications need to be developed and followed.
Etc.
P-91 Remediation
If there‟s an issue:
◦ Can you leave it alone?
◦ Can you remove/replace now or later?
P-91 Remediation
How do you answer these questions?
◦ Stress/creep life analysis
◦ Hanger inspection/evaluation
◦ Material availability
P-91 Remediation
Long Term?
◦ Maintain a diligent inspection program
◦ Industry Forums
◦ EPRI/SI
“Life Management of Creep Strength Enhanced
Ferritic Steels-Solutions for the Performance of
Grade P-91 Steel” (CSEF)
Material Integrity
Life Management
Kicked off 11/07
Finally…
Are we inspecting enough before a failure occurs ??
Long term performance and experience with P91 in power plant service needs to be shared.
Remember:
◦ Code compliant is not necessarily good enough.
◦ Monitor, monitor, monitor!!!