I. The required cross-sectional area shall be the area of the shell or head required to resist pressure which is given as A. If the sum of A1+A2+A3+A4 is equal to or greater than A the opening, is adequately reinforced. If not, more reinforcement must be added. Usually this be in the form of a reinforcement pad. Its area is found as follows.
A - (A1+ A2+ A3 + A4)= Area required for the repad.
REPAD
A5
This type of problem can get complicated very quickly, mostly by the number of steps involved. However, the API 510 Exam Body of Knowledge has simplified the problems. This was done by limiting this type of problem as follows:
b. The nozzle will enter at 90 degrees to the shell or head.
c. The opening will not pass through a Category A weld.
d. Nozzles and shell will be of the same strength.
e. The required thicknesses of shells and nozzles will be given.
In the following example, the problem will be worked using those guidelines. Remember, this type of problem is worth no more than simplest Code calculation possible on the exam. Plan your study time with this in mind. Since the problem may not even be on the if you spend all your time studying these and nothing else, the outcome is obvious. Also, unless you are really comfortable with these problems, it is best to do them last. They eat up a lot of time and you could find yourself rushing through the remaining problems--not a desirable situation!
The API 510 Body of Knowledge has placed the following limits on reinforcement problems.
The inspector should:
a. Understand the key concepts of reinforcement. -Replacement of strength removed
-Limits of reinforcement
-Credit can he taken for extra metal in the shell and nozzle
b. Be able to calculate the required size of a reinforcement pad or to assure a designed pad is large enough. To simplify the problem:
1. All fr = 1.0 2. All F = 1.0 3. All E = 1.0
4. All required thicknesses are given
5. There will be no nozzle projecting inside the shell
The inspector should be able to compensate for corrosion allowance. Weld strength calculations are excluded.
Although it has not been listed under reinforcement, sizing of the fillet welds will probably be required since it is elsewhere in the material.
The best approach is to work a problem typical of what can be expected and explain each aspect above as it is required to solve the problem.
Problem:
A vessel made of SA-515-gr. 70 rolled and welded plate is having a 6 inch NPS schedule 80 seamless nozzle added similar to Fig. UW-16.1 (a) with a fillet weld of 1/2" in leg dimension. The shell's actual thickness is 7/8 inch. The nozzle's actual thickness is 0.432", and it has an O. D. of 6.625". A corrosion allowance of .125" is required.
Givens:
1. The required thickness of the shell is .690" 2. The required thickness of the nozzle Is .033"
3. The nozzle will not pass through a vessel Category A weld : E = 1.0 4. The nozzle will enter the vessel normal to the vessel wall : F = 1.0 5. The nozzle and shell are of the same strength or the nozzle has a
greater strength : fr = 1.0
6. A corrosion allowance of .125” is required.
Drawing:
t = .432"
leg =.500"
t=.875"
Step 1. Check the fillet weld throat size. The fillet weld throat in this Figure of UW-16 is indicated as tc. In the nomenclature of paragraph UW-16, tc is required to be not less than the smaller of 1/4" or 0.707 tmin. Our tmin is the nozzle which is .432".
.707 x .432" = .305" So tc can be no smaller than 1/4"(.250").
Since the throat size of a fillet weld is determined by multiplying .707 times the leg size and our leg size is given as ½”. We calculate as follows.
.707 x .500" = .353". This is larger than and the throat of the fillet weld is adequate.
Step 2. Check to see if a corrosion allowance is specified. If so it must be deducted from the actual thickness of the shell and nozzle prior to calculations. Also the I. D. of the nozzle must be increased by two times the corrosion allowance. In our problem the corrosion allowance is .125".
Nozzle I.D. O. D. -2(wall t - c.a.) Nozzle I.D. 6.625-2(.432-.125) Nozzle I.D. 6.625-2(.307)
Nozzle I.D. 6.625-.614 = 6.01 " Adjusted for corrosion
Step 3. Set up the formulas of UG-37 using Figure UG-37.1 A = d tr F +2tn tr F(1 -fr1) Area required
= d(E1t-Ftr)-2tn(E1t- Ftr)(1-fr1)
A1 OR Area available in shell;
use larger
= 2(t+tn)( E1t-Ftr)- 2tn (E1t-Ftr)( 1-fr1)
= 5(tn –trn) fr 2t
A2 OR Area available in the nozzle outward; use smaller = 5(tn –trn) fr 2tn
A41 = Outward nozzle weld = (leg)2fr2 Area of outward fillet
If A1 + A2 + A41 ≥ A Opening is adequately reinforced If the sum of all the areas are not equal to or greater than A; the area required for the repad is found by subtracting the sum from A.
t shell = .750”
I.D. = 6.01” c.a. =
.125”
All dimensions after corrosion allowance
Step 5. List Givens Adjusted for corrosion:
d= 6.01 " diameter of the finished opening less corrosion t= .750" actual thickness of the shell less corrosion tr= .690" thickness required in the shell per UG-27(c)(1 tn = .307" actual thickness of the nozzle less corrosion trn= .033" thickness required in the nozzle per UG-27(c)(1) E= 1.0 nozzle does not pass through any weld seam F= 1.0 nozzle enters shell at 90 degrees to the shell fr= 1.0 nozzle and shell stress allowables the same Leg size = . 500”
Step 6. Plug values into formulas and solve:
A= 6.01" x .690" x 1.0 + 2 x .307" x .690" x 1.0 x (1-1) Area required A= 6.01" x .690" x 1.0 + 2 x .307" x .690" x 1.0 x (0) Area required A= 6.01" x .690" x 1.0 + 0
A= 6.01" x .690" x 1.0 = 4.1469 square inches Area required
A1= 6.01" x ((1.0 x .750")-(1.0 x .690"))-2 tn (E1t- Ftr)(1-1) A1= 6.01" x ((1.0 x .750")- (1.0 x .690"))- 0 A1= 6.01" x (.750"- .690") = .3606 square inches OR A1= 2(.750"+ .307")((1.0 x .750")-(1.0 x .690"))- 2tn (E1t- Ftr)(1-1) A1= 2(.750"+.307")((1.0 x .750)"-(1.0 x .690"))-0 A = 2(1.057")(.06) = .12684"
Reinforcement For Openings In Shells And Heads Exercises
1. When calculating reinforcement, from what parts must a corrosion allowance be deducted (where)"
2. As regards reinforcement how is the area A found? State the formula.
How many points is a reinforcement calculation worth on the exam? How many points
UG-84 Charpy Impact Tests
Overview
A major concern in vessel operations at low temperature is brittle failure of the material. This type of failure is considered more serious than a ductile failure simply because it is sudden, giving little warning (almost no bulging), and the material might shatter similar to broken glass. Impact testing is required to determine if a material thickness at a given temperature is likely to fail in that manner. Put more directly, the goal of impact tests is to prove it is unlikely to occur in the thickness/material combination being used at a design pressure and minimum design metal temperature (MDMT). The term Low Temperature can be misleading. When welded, 4 in. material thicknesses are considered in low temperature operation at 120°F. Again the first conclusion drawn from UG-84 must be that the tests are required.
For the API-510 candidate, impact testing applies to Part UCS Carbon and Low Alloy Steels of Sub-Section C. These steels are susceptible to brittle fracture even at fairly high temperatures. It should be concluded that impact tests are required on these materials and their weldments. The only exemptions are given in part UG-84 of the General Requirements and UCS- 66, 67, 68 and in UG-20(f). The search for exemptions for a given problem start in UG-20(f) and then continue through paragraphs UCS-66, 67, and 68. This process will be covered in Part UCS of this course.
UG-84 states that impact test shall conform to the paragraphs of SA-370. This is a reference to a standard listed at present on Table U-3 of Page 5 in Section VIII of Division 1, 1992 edition. Look up this table and read it; a question could come from here. It outlines the test apparatus and procedures.
The only kind of impact test recognized by the Code is the Charpy V Notch type. The impact test specimens for a full size test are to be as shown in Fig. UG-84.
The next consideration is that of the minimum absorbed energy for the impact test specimen. Figure UG-84.1 is used to determine the value of absorbed energy required for a test specimen made of carbon and low alloy steels. Notice it refers to those materials listed in Table UCS-23 and that the minimum specified yield strength and thickness of material or weld in inches are crucial for determining impact absorbed energy.
plate.
For test plates 1 1/2 inch or less two sets of three (3) specimens must be taken. One set from the weld with the notch located in the weld as shown in Fig. UG-84 and one set from the heat affected zone (HAZ) with the notch located so that as much HAZ material as is possible is included in the resulting fracture.
For test plates over 1 1/2 inch three sets of three (3) are required. One set from the weld metal and one from the HAZ. A third set is required to be taken from the weld metal as near as is possible to the center of the weld.
The acceptance details for these impact tests is found in UG 84 (c)(5)(c)(6) and in the notes of Fig. UG-84.1. Figure UG-84.1 is used to determine the minimum acceptable absorbed energy for a set of test specimens. To use Figure UG-84.1, the material thickness is found along the bottom of the chart. From that point, move straight up to the line that represents the minimum yield of the material wider consideration, then left to the value of absorbed energy required to pass the test. Notice that this value is called an average. GENERAL NOTES at the bottom of the chart require that no one specimen shall have an absorbed energy value less than 2/3 of the average required for all three.
UG-84 Charpy Impact Tests Exercises
1. What specification must impact testing procedures conform to?
2. What type of Impact test does the Code recognize?
3. What are the dimensions of a standard Charpy Impact specimen?
4. How many specimens comprise a single set?
5. How many sets of specimens are required for a weld procedure test coupon 1 3/4
inches thick?
6. When welding a procedure test plate for impact testing what must the P No. and
Group No. be? What type of heat treatment must be applied to the test plate?
7. Name the two types of test specimens required for all welding procedures. Hint,.
Low temperature should always be a consideration when designing a vessel of carbon and low alloy steels simply because low temperature is defined to be different temperatures for different metals and their respective thicknesses. Example UCS-66 (3) states that if the governing thickness of a non-welded part exceeds 6", and the minimum design metal temperature (MDMT) is colder than 120°F, impact tested materials shall be used. This example has been used to point out how relative the term low temperature is. Turn your attention to figure UCS-66 Impact Test Exemption Curves, In this figure you will find a graph and listing of carbon and low alloy steels. It is limited to 4 inches for welded construction. This is because above 4 inches, welded construction must be impact tested. A good essay or multiple choice question could be taken from this material.
Understanding figure UCS-66 is essential.
Figure UCS-66.1, titled Reduction of Minimum Design Metal 'Temperature (MDMT), without impact testing allows for the reduction of the MDMT when a material in tension is being used below the maximum allowable design stress of that material.
UCS-67 Impact Testing Of Welding Procedures
UCS-67 details three cases where impact tests shall be made on carbon and low alloy steel welds when qualifying a low temperature welding procedure. This is done if impact tests are required for the base metal.
UCS-68 Design
Design rules for carbon and low alloy steels stipulate requirements as to how construction will be performed. The main points are mandatory joint types, required post weld heat treatments below -50°F and their exemptions. Also notice a reduction of 30°F below that of Figure UCS-66 for P-1 materials if post welded heat treatment is performed when it is not otherwise required.
Impact Testing Exemptions
Overview
The first paragraph of UG-84 states that impact testing is required of all weldments, materials, etc., that required to be tested in Subsection C. From this point, the search begins to see if a material or weld is required to be impact tested. The goal is to find an exemption. The search will begin in UG- 20(f) and progress through UCS 66, 67 and 68. If no exemption is found impact tests are required. The best approach is to list these by steps.
UG-20 Step 1. UG-20(f)
UG-20(f) lists an exemption from impact testing for materials that meet all of the following requirements.
1. Material is limited to P No. 1 Gr. No. 1 or 2 and the thicknesses don't exceed the following:
(a) 1/2 in. for materials listed in Curve A of Figure UCS-66. (b) 1 in. for materials from Curve B. C or D of Figure UCS-66.
2. The completed vessel shall be hydrostatically tested (Pneumatic test is not permitted for this exemption)
3. Design temperature is no warmer than 650°F nor colder than -20°F. 4. The thermal or mechanical shock loadings are not controlling design.
Table UCS-66. The Graph and Table are used to determine the minimum temperature a material thickness can be operated at without mandatory impact testing. The graph has four curves: A, B, C and D. In Figure UCS-66 along with the graph is a listing of carbon and low alloy steels. This listing of materials is used to determine the curve on the Graph or in the Table for a given material. After finding the curve for the material, there are two choices. Use the graph of Figure UCS 66 or the Table UCS 66 to determine the minimum temperature for a given thickness. It is recommended to use the Table. The Table and the Graph are the same. The Table is a lot easier to use with accuracy. USE THE TABLE. If the material thickness is operated at or above the temperature listed in Table UCS-66, impact tests are not required. If the material thickness is to operate below the given minimum temperature, impact testing is required. The temperature found in the table is the MDMT of that material thickness without Impact Testing being required.
Step 3. UCS-66(b)
When a material in tension is being used at some stress value below its allowable design stress at the MDMT, a reduction in temperature is permitted This reduction is subtracted from the given temperature for the material in Table UCS 66. If after taking the reduction. the resulting temperature is colder than the minimum design metal temperature desired for the vessel, impact testing is not required. This is called the coincident Ratio. When a material is operating at a relatively high temperature it has lower stress allowed than at room temperature. Many vessels operate alternating between elevated and low temperatures. The lower stress allowed at the elevated temperature will require thicker material than needed at the lowest temperature.
The thicknesses required for the two temperatures can be different, and normally the thickness required for the vessel is determined using the higher temperature stress allowed. So if at the lower temperature and often lower pressure we have extra wall thickness we can take credit for. How much is determined by calculating the coincident Ratio, then entering Figure UCS-66.1 at the calculated Ratio? Normally on the API 510 Exam, the Ratio is stated, and then all that is required is to apply the graph of Figure UCS-66.1.
If the vessel is in a fixed stationary position and its coincident Ratio is below 1.0, the reduction allowed by UCS-66(b) and Figure UCS-66.1 may be taken only when the following is true.
(b)(1): The MDMT is - 50°F or warmer. If the MDMT is colder than - 50°F.
(b)(2): Impact testing is required of all materials unless (b)(3) applies. If the MDMT is colder than - 50°F but no colder than -150°F and the coincident Ratio of stress is equal to or less than 0.4.
Step 4.
UCS-69(a) Design rules for carbon and low alloy steels stipulate requirements about construction of the vessel or part. The main points are: mandatory joint types, required post weld heat treatments below -50°F unless the vessel is installed in a fixed (stationary) location, and the coincident Ratio of stress is less than 0.4.
UCS-68(b) Welded Joints must be postweld heat treated when required by other rules of this Division or when the MDMT is colder than - 50°F and for vessel installed in a fixed (stationary) location the coincident Ratio is 0.4 or greater.
UCS-68(c) Notice a reduction of 30°F below that of Figure UCS-66 for P-1 materials if post welded heat treatment is performed when it is not otherwise required in the Code. This means that 30°F can be subtracted from the temperature found in Table UCS-66. If the adjusted temperature is below that desire, Impact Tests are not required. It is exempt. If a statement about heat treatment is made in a particular problem the task becomes finding out if heat treatment was required or not. If it is not mentioned, it must be concluded that it was not performed and therefore the exemption cannot be taken.
Givens:
Material = SA-516 Gr.70 normalized PLATE
Thickness = 2”
Min. Yield = 38 KSI
MDMT= -25°F
Coincident Ratio = .85
Step 1 Check for the exemptions of UG-20(f).
Our material applies to Curve D of Figure UCS-66 and exceeds the 1 " limit for exemption. It also exceeds the upper and lower temperature limits of 650°F and -20°F.
Step 2 Checking Table UCS-66 and entering at our thickness on the left and moving across to Curve D column, we find the MDMT of this thickness to be - 4°F. This exemption does not apply.
The reduction of MDMT is 15°F. -4°F
-15°F -19°F
New MDMT allowed without impact tests is -19°F. Our MDMT will need to be -25°F so we are not exempted.
Step 4 Checking UCS-68, we find that we cannot take a reduction because PWHT is a requirement of UCS-56 for this material's thickness.
UG-20 / UCS-66 / 68