Advanced methods for sampling and analysis of post-tensioned concrete tendon greases

Rich Wurzbach

ASNT Level III, Infrared and Thermal Testing Laboratory Lubricant Analyst (LLA-I)

MRG Labs, York, Pennsylvania, USA

Overview Background of tendon grease testing Failures of post-tension tendons Comparison of as-found conditions,

failures, to routine grease testing Root-Cause failure analysis and corrective

actions Enhanced sampling methods Expanded grease analysis techniques

Background Some nuclear containment designs

include ungrouted post-tension concrete tendons

Tendon sheaths and anchorhead areas are filled with a corrosion protection grease

ASME Section XI, IWL-2525 Table 1 contains guidance for corrosion protection grease testing, requires 125g sample minimum

Table IWL-2525-1

Status of referenced tests ASTM D992 was withdrawn in 1983 Current version of ASTM D4327 allows for

testing of all three ions, but IWL-2525-1 specifies this for nitrates only, requires two other tests to be performed.

APHA tests are for environmental and wastewater; often requires samples being split between labs, or being run by inexperienced personnel, may require refrigeration of prepared sample

Total alkalinity test does not fall within the scope of current ASTM standard.

Sampling Challenges Quantity required for current IWL-2525

test slate requires disassembly of tendon anchors can, disturbing anchor area during sampling

Harvesting of grease may disturb position of buttonheads, hiding broken strand indications

Invasive nature of sampling requires costly logistical support, equipment, time, scaffold, etc.

Tendon Anchor and Can

Containment Tendon Grease Tendon failure at US

nuclear power plant prompts RCFA, CAR

IWL, Section IX requires 125g grease

Test slate for 2 grams grease developed; tool for sampling remotely

Grease thief and T-handle Provide method to sample grease near anchor without

disassembly Design consistent with ASTM D7718 Standard

Practice for Obtaining In-Service Samples of Lubricating Grease

T-handle and stinger probe allow sampling grease from face of anchor

Results from Small Volume Test (SVT) correlated to disassembly method (large volume sample)

Sampling saved ~US$500,000 in maintenance costs

Water – D95 (IWL-2525)

Uses distillation glassware Per ASTM: “The amount of water as determined

by this test method…to the nearest 0.05 or 0.1 volume%”, which is 500-1000ppm. 

Per Noria Training: D95 “is fairly cumbersome and requires a comparatively large sample to ensure accuracy, which is why it is rarely used in production-style oil analysis labs today”

Water – Karl Fischer (SVT)

Per ASTM: KF allows “direct determination of water in the range of 10 to 25,000” ppm

Can be performed on grease via “oven method” to eliminate interferences and improve accuracy

Only a small volume of grease required (about ¼ gram)

Water Testing Comparison

Image courtesy Noria Corporation, USA Images courtesy Metrohm USA

SVT

IWL

Total Alkalinity Testing Uses an “ASTM Modified” procedure. Per ASTM: “determination of acidic or basic

constituents in petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and isopropyl alcohol.”

Per ASTM: “This test method is not suitable for measuring the basic constituents of many basic additive-type lubricating oils. Test Method D4739 can be used for this purpose.” Visconorust contains basic detergents

Total Alkalinty Comparison Method developed using 0.5 grams

grease and smaller solvent amount Grease fully dissolves, acidification

process followed Titration performed with both colorimetric

and potentiometric (D4793) methods, correlating results

Titration performed per IWL-2525 and new small volume method, correlating results

Ion testing

Two of three methods in IWL-2525 allow for ion-specific electrodes

New method for small volume ion-specific electrode method under development

Can create more repeatable, reliable, and quicker test for ions, Chloride, Nitrate and Sulfide

SVT Small Volume Test Slate Ferromagnetic Iron (ppm) – tested with a Hall-effect

sensor Metals spectroscopy – multiple elements, ppm (iron,

calcium, etc) Moisture, ppm Total Base Number (alkalinity) – using 0.5g sample Red oxide count (corrosion particulate by microscope or

direct-imaging sensor Die Extrusion Index – evaluating unexpected softening or

hardening of the grease Microbial content – quantification of ATP by grease thin-

film extraction

Analysis Techniques

Sample is received. fdM+ is run Grease Thief Analyzer is performed and substrate is made

Two strips are used to make a dilution to run RDE/ICP.

One Strip is used for FT-IR.

One Strip is Dissolved in Green RULER solution to run RULER.

Ferrographic analysis and Red Oxide quantification

Results

Data compiled for 500 tendon locations Strongest correlation between related

parameters (Calcium and TBN, Red Oxides and Ferrous Debris)

Some high Red Oxides were found in higher Total Alkalinity locations

Multiple potential failure modes likely contributor to lack of consistent correlation

Results

Results

Results

Results

Analysis of Data Not a clear single failure mode

represented by correlated data Several tendons identified for further

testing: high ATP (microbial), several high Red Oxides, & high Red Oxide/Low TBN

Testing showed majority of tendons in good condition, small percentage candidates for disassembly and inspection

Advanced statistics package used for ranking metrics

Analysis of Data Dispersion analysis: failed tendon

exceeded 2σ outside the mean for the failed tendon for three parameters

Data analysis by Dr. David Polk, Polk-Lepson Research, USA http://www.polk-lepsonresearchgroup.com/

Analysis of Data Regression analysis performed using Red

Oxides as the dependent variable (actual measure of corrosion) and assigning weighting factors for scoring

Failed tendon and one other scored 5, and twelve others scored as 4.

Data analysis by Dr. David Polk, Polk-Lepson Research, USA http://www.polk-lepsonresearchgroup.com/

Summary Tendon failure modes require reliable and

cost-effective method for sampling and analysis

Using new sampling tools per ASTM D7718 without tendon can removal

Small volume testing methods shown to be equivalent or superior to traditional testing

Additional failure modes detectable with small volume test slate