Material Selection for Oil and Gas Material 3

Question 8

Select a list of materials to fabricate a 2 m diameter by 4 m tall pressure vessel to be used in a processing stream in the Syncrude plant. The operating parameters are such that the environment is acidic, pH=4, there is a presence of oxygen and the tank contains a brine comprised of sulphate ions and bicarbonate ions. It operates under constant pressure and at a temperature of 45oC.

Solution

For this question, safety criteria for this very critical because of the high human risk involved. The following conditions should be used:

εf ≥ 0.20

KIC ≥ 120 MPa√m

We made the following assumptions:

Constant well pressure of 2500 kPa

Constant temperature of 45oC

Thickness of pressure vessel is 2.5cm.

Diameter of vessel is 50 cm

Hoop Stress

We must calculate the hoop stress to get a better understanding of the internal pressure. We used the following to calculate this:

For the considerations, we have stated the primary, secondary, and other considerations:

Industry Standards

Through research, we have found that most pressure vessels built today use AISI 304 AND AISI 316 Steels. Another used for larger diameter and thinner walls is AISI 4130.

Some of the data could not be located, therefore, we were not able to fully complete the table. However, for Corrosion resistance, SCC and Weldability, we used a grading system to easier create our CCR.

Materials Properties Table:

From the CCR, we can see that AISI 410 T&Q230 is the best choice of material, but because the εf < 0.20, it must be struck from the list. Therefore, second in line is AISI 410 Q&T650. This is the best choice overall, given that our εf meets required specs. We take a look at the above table to ...

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Materials Properties Table:

Question 9

Develop or establish a robust technique that can be used to predict the thermal conductivity of steels and alloy steels including austenitic stainless steels.

Solution:

This was a very difficult technique to develop. After discussions with Dr. Shaw and other students, we tried to model a robust technique for Steels, Steel Alloys, and Austenitic Steels. To do this, we build a table of several of the elements with their weight percentage C and other alloying elements along side the thermal conductivities. From this table, we plotted weight percentage of the carbon verses Thermal Conductivity (K). We did try to create similar method for finding K with the aid of other alloying elements such as Mn, P, S, Si, Cr, Mo, Ni, N, Nb, & V. However, we did not have enough information to create accurate and valid charts. Therefore, using the Carbon Content for each metal type we created the following

Steel

For this technique, we plotted the Carbon percentage with the thermal conductivity for plain Steels.. From this we developed an equation which will give us our value for K according to carbon percentage:

Equation of Steel Graph:

K = -3.7039(Wt%Carbon) + 52.013

Stainless Steel

For this technique, we plotted the Carbon percentage with the thermal conductivity for Steels Alloys. From this we developed an equation which will give us our value for K according to carbon percentage:

Equation of Steel Alloys Graph:

K = 36.933(Wt% Carbon) + 20.564

Austenitic Steel

For this technique, we plotted the Carbon percentage with the thermal conductivity for Austenitic Alloys. From this we developed an equation which will give us our value for K according to carbon percentage:

Equation of Steel Alloys Graph:

K = 32.5(Wt% Carbon) + 13.65

Question 10

A copy of a new NACE standard MR0175 is found on in the reading resource room. Summarize the important points that you need to use or consider when using this standard for selecting materials for a sour service application.

Solution:

NACE MR0175 or Application concerning sour oil and gas handbook contain the following information and considerations.

Prior to Material Selection

Question 11

You work for a pressure relief manufacturer and he has assigned you the task of selecting a material for the helical spring to be used on a new series of pressure relief units. The units are to be attached to the top of small pressure vessels that operate at 340 oC.

Solution

Application:

In the oil field, a PRV (pressure relief valve) is a critical safety component of pressure vessels, separators, and anything else under high pressure. It protects the vessel for undergoing unsustainable pressures by bleeding out excess fluid (primarily gas). In this question, we will be looking at designing a helical spring that will act as pressure relief. We may look at ASME Section VIII, Div. 1 – Pressure Vessels as well as ASTM A 125 Standard Specification for Steel Springs, Helical, Heat-Treated.

Because it is very hard to find fatigue strength of the desired materials, we used the following formula fot

Raw Materials

We found that in industry, steel alloys (carbon, oil tempered, chrome silicon and vanadium) are the most common materials for springs. Stainless steel is also common.

Other metals include beryllium copper alloy, phosphor bronze, and titanium.

We have compiled a list and ranked them in order via, CCR. We were unable to find the values for some of the metals/alloys, so we left them out.

From the above table, we can see that AISI 302 and AISI 5160 Oil Q&T 540C have the best CCR. However, AISI 302 does not pass the Scaling Temperature Criteria of 340oC. AISI 5160 Q&T does not live up to the ductility Criteria. Therefore, we are left with the rest of the materials. The CCR clearly shows hat AISI 5160 is the best metal to use.