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Introduction to Pressure Relief Devices - Part 1

Introduction to Pressure Relief Devices - Part 1

When the pressure inside equipment such ...

Is Your Company Ready for The New Reality?

Is Your Company Ready for The New Reality?

Since August, 2015, when VMA’s 201...

Offshore Oil Extraction and Transportation

Offshore Oil Extraction and Transportation

Offshore oil facilities come to the fore...

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Industry Headlines

ITT Reports 2015 Fourth-Quarter, Full-Year Results

1 DAY AGO

On a GAAP basis, ITT delivered revenue of $2.5 billion in 2015, reflecting a 6% decline, primarily due to the impact of unfavorable foreign exchange of $194 million. GAAP operating income increased 43%.

Organic revenue in the Industrial Process segment decreased 6%, reflecting strength in short-cyc...

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MRC Global Signs Agreement to Sell OCTG Business

2 DAYS AGO

MRC Global Inc. has entered into a definitive agreement to sell its U.S. Oil Country Tubular Goods (OCTG) business to Sooner Pipe, LLC, a subsidiary of Marubeni-Itochu Tubulars America, Inc., for $48 million, subject to certain adjustments.

MRC Global's U.S. OCTG sales were approximately $305 milli...

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EPA Halts Implementation of Clean Power Plan

1 DAY AGO

Earlier this week, in a 5-4 decision, the U.S. Supreme Court granted an industry motion to stay the EPA’s Clean Power Plan while the lower courts determine its legality. Last fall a lawsuit was filed on behalf of more than two dozen states, utilities and industry groups.

“States did not...

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IHS: North American Drillers Need Billions More in Cuts

3 DAYS AGO

The depressed oil price environment is painting a gloomy outlook for North American exploration and production (E&Ps) companies, and further, significant CAPEX cuts are needed in order for the group to demonstrate real financial discipline and align spending more closely with cash flow, accordin...

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U.S. Job Openings Climb to Second-Highest Level on Record

4 DAYS AGO

The number of job openings increased to 5.6 million in December, the second highest number ever recorded, the U.S. Bureau of Labor Statistics reported today. Hires and separations were little changed at 5.4 million and 5.1 million, respectively. Within separations, the quits rate was 2.1%, and the l...

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Machine Tool Orders Rose in December, Down in 2015

4 DAYS AGO

The U.S. Manufacturing Technology Orders report for December 2015 showed that order values grew 20.4% compared to the prior month, according to The Association for Manufacturing Technology (AMT). For all of 2015, the year’s total orders were down 17.4% compared to 2014.

While the month-to-mon...

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Testing High-Nickel Alloy Castings in Refineries

vmspr12_nickel_1

Refiners today are increasingly dealing with more corrosive feedstocks that present new demands on valves in the process. However, maintenance personnel can detect problems before they become major issues by using different testing methods.

In 2009, a Minnesota-located refinery was experiencing through-wall leakage with several Class 300 rotary valves tasked with controlling crude unit vacuum prefractionator charge heaters. Maintenance personnel removed insulation from the valves and noted coke residue on the surface of the valve bodies, which identified for them where the leaks were occurring (Figure 1).

vmspr12_nickel_fig1Figure 1. Removing insulation from around the ball valve in question revealed leakage locations.Fortunately, this particular situation did not result in a safety event or a fire. Instead, it illustrates how the refining industry’s use of increasingly corrosive feedstocks can combine with unknown casting defects to cause potential valve problems.


THE INVESTIGATION/ EVALUATION

Five valve body castings, all grade CW2M (cast alloy C), were returned from the refinery to the manufacturer for evaluation using both nondestructive and destructive tests.

The nondestructive tests performed on the returned castings included visual examination, pressure testing and liquid penetrant (LP) examination.

Visual examination did not reveal any signs of corrosion on the wetted casting surfaces of the returned valves, which included both as-cast and machined surfaces.

The pressure testing used water at 1125 psig (7.76 megapascals or MPa) followed by helium at 150 psig (1.0 MPa). LP testing was performed to the requirements of ASTM A903 Level III, which considers linear and rounded indications exceeding 3/16 inch (4.8 millimeters) to be relevant. The helium and hydrostatic water tests revealed no leaks. Apparently, the hydrocarbon or potential coking sealed the leak paths once the valves were brought down to ambient temperature and removed from service.

LP testing of the castings revealed indications on the exterior surface—a lesser number of indications were on the interior, cored surfaces. These indications were on both as-cast and machined surfaces. Most of the LP indications were shallow [<0.02 inch (0.5 millimeters)] and removed with minor grinding. However, on the neck area of some castings, grinding did not remove the indications. The defect progressed through the wall of the casting and could represent a leak path. (Note that all of the returned valves had through-wall leaks in the neck area.)

Destructive testing, including metallographic examination, scanning electron microscopy (SEM) and energy dispersive spectrographic analyses, was performed on several of the returned castings.

vmspr12_nickel_fig2Figure 2. Opened defect showing three zones of fracture. Original magnification 11x. For example, corrosion testing was done on one valve body casting to compare results to maximum acceptance values previously set for this material grade. The test environment was boiling ferric sulfate-sulfuric acid per ASTM G28 Practice A. Although this standard is intended for wrought product forms, the practice A test method is also useful for castings. The corrosion rate was 140 milli-inches per year or mpy (3.5 millimeters/year or mm/y) compared to the manufacturer’s acceptance criteria of 360 mpy (9.1 mm/y) maximum. The grain boundaries were visible, which is typical for this grade. Of importance to this issue is the fact that this is a very severe test that does not represent actual applications for CW2M but does detect susceptibility of weld metal and heat-affected zone to intergranular corrosion attack.

vmspr12_nickel_fig3Figure 3. Rounded dendrite fingers indicating a shrinkage defect. Original magnification 600x.Fracture surfaces from the neck area of the same valve body were examined using SEM (Figure 2). The first zone examined was an outer layer that was approximately 0.03 to 0.06 inch (0.8 to 1.5 millimeters) thick. This chill layer solidifies rapidly when the molten metal first contacts the mold surface.

The second layer or zone 2 of the fracture has a dendritic pattern. This pattern represents columnar grains that grew perpendicular from the chill layer during the balance of the solidification process. The neck was cast solid so all the grain growth was from the outer diameter to the center. The center of the neck was then bored out during machining of the casting.

Zone 3 was ductile, dimple shear. This is the fracture mode seen on any mechanical break produced in the lab.

Within the dendritic zone of some of the fractures were rounded dendrite arms (Figure 3). The rounding indicates a shrinkage defect caused by an isolated area of liquid that was frozen off from the riser system because it was not properly fed. When the liquid was consumed during solidification, the dendrite arms could not continue to grow, leaving the blunted tips. Dark areas, which were identified as oxide films formed from exposure to air during casting solidification or heat treatment, were also found on the lab fractures. This proves the fractures were present before the casting went into service.

vmspr12_nickel_fig4Figure 4. Photomicrograph showing the leak path and the continuation of the grain boundary. Original magnification 500x.Inclusions and porosity also were visible. The inclusions were mold sand, slag and oxides. The grains were very large compared to wrought product forms—about 1/4 to over 1/2 inch (6 to 13 millimeters). The grain boundaries were the intersection of the dendrites formed during solidification. One leak path was cross-sectioned (the photomicrograph in Figure 4 shows the continuation along a grain boundary).

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