Emerald Metals LLC

Integrity Testing of CLADMAX Low Chromium Alloy Tube Internally Clad WithAlloy 825 Tubes

CLADMAX provided a 31/2 inch diameter seamless tube made of 0.295 inch thick low chromiumalloy steel tube base metal internally lined with 0.0625” thick Alloy 825, marked “EM-07-03-925-001”. This composite tube was reportedly made from 21CrMo10 and Alloy 825 (Figure 1)followed by pilgering of the composite billet formed through centrifugal casting.

Conclusions:

As per the following statements, bonding between the internal clad and the base metal passed allmechanical tests. However, problems arose when making root bends in pipe to pipe welds. Also,some base metal mechanical properties and chemical analyses did not meet expectedrequirements. Summary test results follow.

1 – The composite tube passed the flare test, though it cracked just as it reached the minimumrequired diameter expansion.

2 – The composite tube passed a flattening test.

3 – No disbonding occurred during sectioning, machining, cyclic heating (1200 to 1700 °F) awater quench test, and a cross-shaped welding joint tensile test

4 – Four root bends from two different circumferential welds broke – possibly caused bycontaminants in the clad-to-base metal interface.

5 – Measured compositions of several elements in both the tube’s base metal and internalcladding fell outside of specified tolerances.

6 – Hardness test results and microstructure, suggest that the tube’s base metal mechanicalproperties may be different than those expected for SA-213, grades 11 or 12 properties.

Examination:

The tube piece exhibited no visual scale or surface flaws. Mechanical testing followed therequirements of the “Specification of Manufacturing, Testing and Inspection Procedures”. A 21/2inch long tube piece flattened according to the testing requirements in ASME SA-450 met thespecified requirements by exhibiting no cracks or flaws when the distance between flatteningplates dropped to less than 1.95 inches. As flattening continued, fracture occurred where outsidesurfaces experienced the most deformation, 90° from the flattening plate contact points (Figure 2).Fracture initiated from the outside surfaces, but changed direction at the bond interface where itfollowed the clad to base metal bond line. No fractures revealed any flaws or unsound base or cladmetal.

One fracture developed during a flaring test performed according to SA-450 on a 4 inch longspecimen. The fracture occurred just as the tube mouth at the cone insertion point reached theminimum specified 15 % inside diameter expansion, though short of the SA-450 minimumrequired 21% expansion (Figure 3). Cracking initiated at the tube’s outside edge in the low alloysteel base metal. Forcing the cone further into the tube to expand the flare (to 27 %inside diameter expansion) caused the crack to extend, but no flaws developed on theclad surface.

A heat and water quench test used a nearly flat 2'/2” x 2'/2” piece cut from the tube specimenpreviously used for the flattening test (Figure 4). After heating to 1200 °F, the piece wasimmediately dropped into a container of 70 to 90 °F water. After repeating this process 9more times while increasing hold temperatures by 50 °F each time, with a final temperatureof 1700 °F, the piece exhibited no visible cracking, or disbonding between the internal cladand the low alloy steel tube.

No clad-to-steel tube disbonding developed during a cross-shaped welding joint test asprescribed by the Babcock-Borsig, “Specification of Manufacturing, Testing and InspectionProcedures” (Figure 5). This specimen was fabricated by attaching 1.875” wide by 0.354”straps to opposite sides of a 1.875” long half circumference piece of the composite tube.Total fusion line width of the GTAW attached steel to Alloy 825 surface, using ERNiCrMo-3, measured 0.842”. Fracture occurred in the steel strap, 11/8 inches away from the Alloy 825surface, at a maximum load of 52,877 lbs for a measured steel bar tensile strength of 74,285 psiand approximate load across the ERNiCrMo-3 to Alloy 825 clad weld fusion line of 33,500 psi.Therefore, this tube piece met test requirements.

Microscopic examination of a cross-section on the non expanded end of the flare testspecimen and perpendicular to the flare test crack found no obvious metallurgical features thatmight have contributed to the flare test or weld root bend fractures. The 1 % chromium alloymicrostructure contained somewhat shperoidized carbides with a thin (75 μm) decarburizedlayer at its surface. Precipitates at the grain boundaries suggest that the internally clad Alloy825 microstructure sensitized during production (Figures 6 and 7). A few very shallowintergranular cracks also originate from the inside surface (Figure 8).

Bench top hardness testing on the cross-section measured the base metal hardness as aboutRockwell C-22. A Beijing Changxing Composite Material Development Co., Ltd. TestingReport, MTR No. YP001-09-2010, reported “shell” hardness values of 27.5 and 30 RockwellC.

To evaluate weldability a 1/3 circumference butt weld between two 3 inch long pieces of thetube were joined by gas tungsten arc welding, with argon purge, using ERNiCrMo-3 (a welddeposit composition similar to N06625 or Alloy 625). However, both root bends, cut andtested according to ASME IX requirements broke and failed. Fractures appeared tooriginate from dark planar flaws in the weld deposit. Both root bends also failed in asecond attempt, though the welder utilized thorough grinding between passes to assureremoval of any surface oxides which could contribute to incomplete fusion were removed(Figures 9 and 10).

Optical emission spectroscopy (OES) measured the alloying content in the base metal “Tube”and “Internal Layer” as reported (weight %) in the following table. The table also recordslow chromium alloy steel (per ASME SA-213) and Alloy 825 (ASME SA-425) specifiedanalyses requirements and analyses stated in the tube’s MTR.

Element Tube GradeT11

Grade T12 MTR InternalLayer

Alloy 825 MTR

Iron Rem. Rem. Rem. Rem. 31.3 ≥ 22.0 18.9

Carbon 0.188 0.05–0.15 0.05 – 0.15 0.209 0.025 ≤ 0.05 0.021

Silicon 0.501 0.5 – 1.0 ≤ 0.50 0.58 0.56 ≤ 0.50 0.73

Manganese 1.14 0.30–0.60 0.30–0.61 1.14 0.30 ≤ 1.00 0.63

Phosphorus 0.025 ≤ 0.025 ≤ 0.025 0.021 ... ... 0.006

Sulfur 0.009 ≤ 0.025 ≤ 0.025 0.008 0.0016 ≤ 0.03 0.007

Chromium 1.09 1.0 – 1.50 0.8 – 1.25 1.18 23.4 19.5–23.5 26.69

Molybdenum 0.39 0.44–0.65 0.44-0.65 0.42 2.15 2.50–3.50 3.58

Nickel 0.23 ... ... ... 39.6 38.0–46.0 44.7

Copper 0.052 ... ... ... 0.265 1.50–3.0 2.12

Aluminum 0.028 ... ... ... 0.315 ≤ 0.2 ...

Titanium 0.026 ... ... ... 0.53 0.60–1.20 1.39

Vanadium 0.046 ... ... ... 0.014 ...

Niobium 0.032 ... ... 0.022 0.16 ... 0.16

Tungsten <0.001 ... ... ...s 0.076 ... ...

Discussion:

The Babcock-Borsig, “Specification of Manufacturing, Testing and Inspection Procedures”document prescribes several destructive tests according to requirements in ASME SA-450.

Only the fractures along the bond line in the flattening test revealed any weakness for bond lineintegrity. However, this result should not be considered grounds for rejection since other bondline integrity tests passed.

Distortion created during flattening put additional stress on the bond line during the heat andquench test. Though the Babcock-Borsig specification does not require this test, it subjects thebond line to heating and cooling cycles considered more aggressive than those the tube shouldexperience during service.

The clad to base metal bond passed the cross-shaped welding joint test since the 33,500 psi peakload imposed on the clad surface exceeded the apparent Babcock-Borsig, “Specification ofManufacturing, Testing and Inspection Procedures” specified approximate minimum equivalentstress of 28,000 psi

Hardness test values for the 1 % chromium alloy tube portion exceeded the maximum permittedRockwell B-85 for both grades T11 and T12 although the MTR reported even higher values. Thisfact along with the tube production description suggests that some tube properties could besignificantly different from those that ASME specifications require for grades T11 and T12.

Probably due to the heating cycles imposed on the tube during manufacture (casting, co-extrusionand pilgering) carbide spheroidization in the low chromium alloy steel and sensitization of theAlloy 825 clad occurred. Tensile testing can determine if the tube retains adequate strength in thiscondition. Tubes operating at elevated temperatures during service should sensitize anyway,though, so purchasing them in this condition may be acceptable. If not acceptable, a stabilizinganneal may be required.

Unfortunately, the weldability testing results indicated that welding procedures and practices typicallyutilized to join low alloy steel tubes internally clad with nickel alloy will not pass ASME IX weldprocedure qualification testing. Although 1 % chromium alloy tubes should be postweld heat treated forservice, bend specimens made with nickel alloy weld deposits, especially those which stress the cladside on the bend’s outside radius should not crack in the as-welded condition either.

The tube composition best matches the requirements for Grade 12, though measured carbon,manganese and molybdenum contents fell outside ASME SA-213 specified ranges. Measuredcompositions for silicon, molybdenum, copper, aluminum and titanium lay outside the specified rangesfor Alloy 625. (Copper and titanium values were significantly different.)

Key: low alloy steel, composite tubes, co-extruded, flare testing, flattening, Alloy 825, GradeT11, Grade T12, Chinese steel 21CrMo10, broken root bendsCC: ES05.11/6-523-B

Figure 1 – All testing was performed on this 31/2” outside diameter, 18 inch long tube.

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igure 2 – Although the 2'/2” long piece of pipeassed the flattening test, continuing to flatten theiece until opposite inside surfaces touched causedacture as shown. Cracking progressed from theutside until it reached the clad to baseetal bond line where some disbonding took place (between yellow arrow tips). The disbonding

lus short crack extension into the clad, terminating at arrow tips, is 0.40 inches long.

Base Metal

igure 4 – This edge, like the other 3 of the 2'/2” x 2'/2” square piece cut from one flat side of theiece shown in Figure 2 survived water quenches after heating it up to 1200 °F, then 1250 °F,ith seven 50 °F sequentially hotter temperature/quenches until reaching 1700 °F. Visual

xamination found no disbonding between internal clad to base metal.

igure 3 – During the flare test oneongitudinal fracture occurred shortlyfter the inside diameter reached.97” (15% larger than the nominaliameter). No other visuallyetectable cracks developed.

Figure 5 – A tensile load applied to strapson opposite sides of the 1-7/8” widespecimen as depicted in this cross-shapedwelding joint test specimen resulted infracture. Large arrows depict the tensiletest loading applied to the 0.354” thick x 1-7/8” wide straps. Fracture occurred in thetop strap.

. Alloy 825Clad

1 % CrAlloy BaseMetal

Figure 6 – A thin decarburizedlayer, about 75 μm deep) exists in the 1 % chromium alloy steelalong the tubes outside surface.This microstructure comes froma cross-section cut perpendicularto the tube axis and crack at thenon flared end of the test pieceas indicated by the arrow inFigure 3.(Nital Etch)

Figure 7 – Additional magnification of the basemetal microstructure shows that somespheriodization occurred.

Figure 8 – Several shallowintergranular microcracks exist atthe internal cladding’s insidesurface. Etching revealedprecipitates at the grain boundariesshowing that the microstructure issensitized.(Electrolytic Nital Etch)

Figure 9 – All four root bendsspecimens fractured in theweld deposit during thebending operation. (Asuccessful root bend test woulddisplay no cracks longer than1/8”).

Figure 10 – Arrows point tosome of the dark inclusionsthat appear to cause thefractures in the weld depositof one specimen in Figure 9.