Addition of a larger nozzle to a pressure vessel

1

NB members Meeting October 2019- R Ferrell

2

Reinforced OpeningWelded Nozzle Design Plan

Remove an NPS 10 nozzle and replace with an NPS 12 nozzle

Nozzle Alteration Plan

• Replace a NPS 10 outlet nozzle with a NPS 12 outlet

nozzle on a pressure vessel.

• This ASME Section VIII pressure vessel requires

postweld heat treatment. We will use NBIC Part 3

paragraph 2.5.2 local PWHT or Welding Method 1.

• Contact your Repair Inspector to authorize this

alteration and discuss the alteration plan before

quoting the job.

3

Alteration Nozzle

4

Nozzle Alteration Plan

• Reinforcing calculations need to be done to determine nozzle

thickness or the need for a reinforcing element. (UG-37)

– This is done because the cylindrical shell is designed to carry hoop

stress (circumferential stress) caused by internal pressure. Removing

metal by placing a hole in the cylinder disrupts the uniform

distribution of this membrane stress. Therefore, that metal must be

put back (compensation) to absorb its share of the stress load.

• The shell thickness calculation needs to be done to determine

the required shell thickness before calculating available area.

• This shell is made up of one piece of plate. The nozzle is on

the top of the shell.

5

Nozzle Alteration Plan

(known information)

• P=MAWP = 700 psi

• Shell material is SA-516-70 (S= 20,000 psi) with a

maximum design temperature of 500°F and MDMT

of 40°F. (see UCS-66)

• The Manufacturer’s Data Report from the National

Board shows a shell thickness of 1.625 inches, but

there is general corrosion pits 0.125 inches deep

near the nozzle reinforcement area. The original

inside diameter was 48 inches.

6

Nozzle Alteration Plan

(known information)

• The new nozzle is NPS 12 (12.75 inch outside

diameter), SA-106 Gr C, 0.562 inch nominal wall

(SCH 60),

S = 20,000 psi, design temperature is 500°F

• Note:

– when pipe is ordered and received using nominal wall

thickness, a 12.5% under tolerance must be deducted

from the wall for design calculations.

– For example, 0.562 nominal x .875 (subtracts 12.5%) =

0.492 inches

7

Design Calculations

• Both the shell and nozzle are cylindrical components

under internal pressure.

• Therefore, we will use UG-27 (c) 1 to calculate the

minimum required wall thickness for both.

8

9

20 These formulas will govern only when the circumferential joint

efficiency is less than one‐half the longitudinal jointefficiency, or when the effect of supplementary loadings (UG-22) causing longitudinal bending or tension in conjunctionwith internal pressure is being investigated.

UG-27 Shell Calculation

PSE

PRtshell

)6.0(−=

• P = 700 psi

• R = 24.125″

• S = 20,000psi

• E = 1 full radiography

• C = 0 no additive

thickness

10

700)6.0(120000

125.24700

−•

•=shellt

19580

5.16887=shellt

tshell = 0.863”

UG-27 Nozzle Calculation

• P = 700 psi

• R = 5.88325 (subtracted

12 ½%)

• S = 20,000 psi

• E = 1 (seamless pipe)

• C = 0 no additive

thickness

11

PSE

PRt

6.0−=

𝑡 =700 (5.88325)

20000 ∗ 1 − 0.6 ∗ 700

trn = 0.283"

𝑡 =4706.6

16620

Minimum Nozzle Wall Thickness

(see UG-45)

12

The minimum nozzle wall thickness, other than access and inspection openings, shall be not less than the following:

This will result in the prevention of the usage of thin wall nozzles. To join a thin wall item to a vessel, an intermediate fitting will be necessary

ASME Section VIII UW-16.1 Welded Nozzle

Special Rule

13

Necks abutting a vessel wall shall be attached by full penetration groove weld [see (b) above]Necks inserted through the vessel wall may be attached by full penetration groove weld [see (e) above]

TYPICAL

(b)(e)

Special rule controlling weld placement. In most cases it will result with a weld being placed at two points, the intersection of the nozzle on the outside of the vessel shell and at the intersection of the nozzle with the inside of the shell. It is to eliminate an exposed crevice on the inside of the pressure vessel.

Minimum Nozzle Weld Sizing

Defined In UW-16 and Fig. UW-16.1

14

Typical Example:Solve minimum weld sizes (UW-16.2 (b)) also see UW-15 for minimum strengthtmin = the smaller of ¾ in. or the thickness of the thinner parts joined by a fillet, single bevel, or single j weld

tc =not less than the smaller of ¼ in. or 0.7 tmin (this is the throat dimension not leg)

tc

The nozzle is thinner than the shell so:tn= 0.562 inch= tmin

tc=0.7(tmin)=0.393 inchTherefore the minimum leg is .556 inch (9/16 inch)

This is an important step in verification of the nozzle. Should this be done incorrectly, the nozzle could fail. t minimum is a function of the two items being joined. Where reinforcing elements are involved, there will be more than one value of t minimum based on the weld being considered.

Fillet Weld Throat Versus

Leg Dimensions

22 bac +=

15

c

A

B

b

a

C

45

4590

a

Right Angle Triangle(typical fillet weld shape)

Weld leg = Weld throat x 1.4142Weld throat = weld leg/1.4142

Weld leg

Weld throat

B

A

C c

b

22 bca −=

22 acb −=

Section VIII

16

Section I

17

Section IV

18

Area of Reinforcement Required

tn d

ttr

tn = 0.562 in.d = 11.626 in.t = 1.625 in.tr = 0.863 in.F = 1.0fr1= 1

19

A= dtrF+2tntrF(1-fr1)

A = 11.625 x 0.863 x 1 + 0= 10.032 + 0= 10.032 in.2

FIG. UG-37.1

If Nozzle Sn = 17,100 ( Sa -106-B)Then fr1 =0.855 and A would be over 12”.

Area of Reinforcement Available in Vessel

tn d

ttr

tn = 0.562 in.d = 11.625 in.t = 1.625in.tr = 0.863 in.F = 1.0fr1= 1E1= 1

20

A1 = 8.85 in.2

A1 = d(E1t-Ftr)-2tn(E1t-Ftr)(1-fr1)Or

A1 = 2(t + tn )(E1t-Ftr)(1-fr1)USE LARGER VALUE

FIG. UG-37.1

tn d

t

trn

Area of Reinforcement Available in Nozzle External of Vessel

tn = 0.562 in.d = 11.625 in.trn = 0.2985 in.F = 1.0fr2= 0.855

21

UG-37.1

A2 = 5(tn-trn) fr2 tn

Use the smaller value

A2 = 0.784 in.2

tn d

t

Area available in nozzle welds

tn = 0.562 in.tc = 0.398 in.fr2 = 0.855Weld leg = 0.5625 in.

22

UG-37.1

A41= (leg)2 fr2

A41=0.270 in.2

ti d

t

h

Area of reinforcement available on inside nozzle

23

UG-37.1

A3= 2hti fr2

A3= 2 x 1.405 x 0.562 x 1

Use smaller value

Fr2= sn/ss=1

h, 2.5 t, 2.5ti

3.875 , 4.0625, 1.405 A3= 1.58 in2

tn d

t

h

Total Area of reinforcement available

24

A1+A2+A3+A41 ≥ A 11.484 versus 10.032

25

26

27

Evaluate Weld Strength

UG-41(b)

Verify strength of Compensation

• UG-37, UG-41,

• UW-15 b) 1 exempts sketches in UW-16.1

• Our nozzle installation is equal to figure UW-16.1

c)• No further analysis required for weld loading as per UG-41

28

29

30

W is the required

weld strength to attach elements that are not an integral part of the vessel wall

Exempt Openings

Reinforcement Calculation Exception

– UG-36 exempts small openings in vessels not subject to

rapid fluctuations in pressure

• 3-1/2 in. (89 mm) diameter—in vessel shells

or heads with a required minimum thickness

of 3/8 in.(10 mm) or less;

• 2-3/8in. (60 mm) diameter—in vessel shells

or heads over a required minimum thickness

of 3/8 in. (10 mm);

31

Exempt Openings (cont.)

• threaded, studded, or expanded connections

in which the hole cut in the shell or head is not

greater than 2-3/8 in. (60 mm) diameter

• no two isolated unreinforced openings, in

accordance with above, shall have their centers

closer to each other than the sum of their

diameters

32

No centers closer to each other than

the sum of their diameters

33

2 inch dia.3 inch dia.

Less than or equal to 5 inches

PWHT NBIC Part 3 Para.2.5.2

34

Gradient control band ( insulation width)

Caution- the pwht process as well as the nozzle to shell weld may heat the shell enough to relax the shell and cause it to sink in. Additional support should be considered until the heat in the nozzle area has cooled .

2.5.3.1-Welding Method 1

Limited to:

▪ P-No. 1 ( groups 1,2,3), P-No. 3 (Gr 1,2) no Mn-Mo steels

▪ SMAW, GMAW, FCAW, GTAW

▪ Welders and procedures qualified w/o PWHT

▪ Preheat required to 300°F measure 4″ or 4 thicknesses

from joint

▪ 450°F maximum interpass temperature

35

One principle reason for preheating and interpass heating is to prevent hydrogen cracking in the weld metal and /or HAZ. It drives off moisture, reduces the cooling rate and increases the rate of hydrogen diffusion. WRC Bulletin 452

Purchase Order Information

• Nozzle material

– NPS 12 Sch 60 pipe ( 0.562 inch nominal wall)

• SA-106 Gr C

• Cut to an overall length of 29-1/2 inches, square cut ends

(12 inches for welder qualification)

• Mill Test Report required ( not required by Section VIII)

• Material marked in accordance with ASME Section II

– SA-530 Specification for general requirements for specialized

carbon and alloy steel pipe

– SA-106 Specification for seamless carbon steel pipe for high-

temperature service

36

Summary

• Always try to have an alteration plan consistent with

the original code

• NBIC -Part 3 provides acceptable options if the

alteration can not follow the manufacturing practice

used to meet the original code. Make sure the

Owner, Repair Inspector and Jurisdiction accept the

options in the alteration plan.

• QUESTIONS?

37