[S&T HEX] Strength weld tube to tubesheet joint requirement (API660 & TEMA & ASME)

[Shell and Tube Heat Exchanger] Strength weld tube to tubesheet joint requirement (API660 & TEMA & ASME)

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<Strength Weld tube to tubesheet Join 적용 기준>

 

다음과 같은 condition 이 적용될 경우 strength welded tube-to-tubesheet joint 를 적용한다.

 

1. API 660 Para. A.4.4.3

 

Strength-welded tube-to-tubesheet joints should be considered by the purchaser for the following conditions.

 

a) Design Pressure > 7000 kPa

b) Duplex stainless steel tubes in wet hydrogen sulfide service

c) titanium tubes

d) Austenitic stainless steel tubes and ferric steel tubesheet and metal temperature > 205C

e) Fixed tubesheet in sulfur plant application

f) In heat transfer fluid service with Operating temperature > 205C

g) In cyclic service

h) In a service where sudden temperature excursions can occur

i) fy ratio < 0.6 (per Sec VIII, Div1, Nonmandatory Appendix A)

 

기본적으로 압력과 온도가 높거나 특정  service 에서 운전하는 경우 요구된다.

 

 

2. API 660 Para. A.4.4.4

 

Seal welded or strength-welded tube-to-tubesheet joints should be considered by the purchaser for the following conditions.

 

a) where leakage from high pressure side to low pressure side is not acceptable for process reason (steam condensate / cooling water)

b) for exchangers handling steam or boiler feed water at design condition exceeding class 150 flange rating

 

tube joint 의 leak 발생 시 문제가 되는 process 에서는 해당 tubesheet joint 가 요구된다.

 

 

3. API 660 Para. A.4.4.5 

 

In hydrogen, tube-to-tubesheet joints should be strength welded and expanded

a) Design pressure >= 7000 kPa

b) Design temperature > 230C 

 

 

<Fabrication & Inspection Requirement>

 

Strength welded tubesheet joint 를 적용 시 다음과 같은 requirement 를 반영한다.

 

1. API 660 Para. 9.5.6

 

Strength-welded tube-to-tubesheet welds shall have a minimum of two weld passes and be produced by gas

tungsten arc welding (GTAW) using filler material, unless otherwise specified or approved by the purchaser.

 

Min 2 weld pass 로 filter metal 을 이용하여 GTAW 로 용접한다.

 

 

2. API 660 Para. 9.5.7

 

The qualification of the weld procedure for a strength-welded tube-to-tubesheet joint shall be in accordance

with the requirements of the pressure design code, with the following additional requirements.

 

a) min leak path shall not be less than two-thirds of the nominal tube wall thickness

b) min 3 tensile pull test shall be performed on the qualification test coupon whenever it cannot be proven by calculation that the strength of weld is greater than axial strength of tube.

 

Strength weld 계산으로 axial strength 를 견딜 수 있다고 검증하지 못하면 최소 3번의 tensile pull test 를 실시하여야 한다.

Axial load 는 ASME Sec.VIII, Div.1, UHX-13.5.9 의 절차에 따라 검증 할 수 있다.

 

 

3. API 660 Para 10.2.1   

 

In the case of welded-and-expanded tube-to-tubesheet joints, the tube weld integrity shall be verified before final expansion of the tubes by a pneumatic test from the shell side at a gauge pressure of between 50 kPa (7.5 psi) and 100 kPa (15 psi), using a soap-water solution to identify leaks.

 

Tube 용접의 건전성은 shell side 에서 기압테스트를 실시하여 검증한다.

 

 

<Strength Weld Design>

 

1. TEMA RCB-7.3.2.2

 

When welded joints are used to carry the longitudinal tube loads, consideration may be given to modification of the requirements of Paragraghs RCB-7.2 through RCB-7.3.1.

 

일반적으로 weld leg 가 tube 두께의 1.4 배 이상의 경우 strength weld 로 부르며 longitudinal load 를 견딜 수 있게 설계하여 함.

 

 

2. ASME UW-20.4 & UW-20.6

 

해당 requirement 에 따라 axial load 를 견딜 수 있도록 weld size 결정