QW-202.6 Tube-to-Tubesheet Qualification. When the applicable Code Section requires the use of QW-193 for tube-to-tubesheet demonstration mockup qualification

tests, QW-193.1 shall apply. If specific qualification test requirements are not specified by the applicable Code Section, tube-to-tube sheet welds shall be qualified with one of the following methods:

(a) groove welds per the requirements of QW-202.2 and QW-202.4

(b) a demonstration mockup per the requirements of QW-193.1

(c) fillet welds per the requirements of QW-202.2(c) (for non pressure retaining tube-to-tube sheet welds only)QW-193 Tube-to-Tube sheet Tests

When the applicable Code Section requires the use of this paragraph for tube-to-tubesheet demonstration mockup qualification, QW-193.1 through QW-193.1.3 shall apply.

QW-193.1 Procedure Qualification Specimens. Ten mockup welds are required to qualify each procedure. The mockup assembly shall essentially duplicate the tube hole

configuration and the tube-to-tubesheet joint design within the limits of the essential variables of QW-288. The thickness of the mockup tubesheet is not required to be thicker than 2 in. (50 mm) and the cladding may be represented by base material of essentially equivalent chemical composition to the cladding composition. The mockup welds shall be submitted to the following tests sequentially and must meet the applicable acceptance criteria.

QW-193.1.1 Acceptance Criteria Visual Examination. The accessible surfaces of the welds shall be examined visually with no magnification required. The welds shall show complete fusion and no evidence of burning through the tube wall, and shall be free from cracking or porosity.

QW-193.1.2 Acceptance Criteria Liquid Penetrant. The liquid penetrant examination shall meet the requirements of Section V, Article 6. The weld surfaces

shall meet the requirements of QW-195.2.

QW-193.1.3 Acceptance Criteria Macro- Examination. The mockup welds shall be sectioned through the center of the tube for macro-examination. The four exposed surfaces shall be smoothed and etched with a suitable etchant (see QW-470) to give a clear definition of the weld and heat-affected zone. Using a magnification of 10X to 20X, the exposed cross sections of the weld shall confirm

(a) minimum leak path dimension required by the design

(b) no cracking

(c) complete fusion of the weld deposit into the tubesheet and tube wall face

(d) complete penetration of the weld deposit to within 164 in. (0.4 mm) of the root of the joint

(e) porosity shall not reduce the weld throat below the required minimum leak path thickness

QW-195 Liquid Penetrant Examination

QW-195.1 The liquid penetrant examination in QW-214 for corrosion-resistant weld metal overlay shall meet the requirements of Section V, Article 6. The acceptance

standards of QW-195.2 shall be met.

QW-195.2 Liquid Penetrant Acceptance Criteria

QW-195.2.1 Terminology

relevant indications: indications with major dimensions greater than 116 in. (1.5 mm).

linear indications: an indication having a length greater than three times the width.

rounded indications: an indication of circular or elliptical shape with the length equal to or less than three times the width.

QW-195.2.2 Acceptance Standards. Procedure and performance tests examined by liquid penetrant techniques shall be judged unacceptable when the examination exhibits

any indication in excess of the limits specified in the following:

(a) relevant linear indications

(b) relevant rounded indications greater than 316 in.(5 mm)

(c) four or more relevant rounded indications in a line separated by 116 in. (1.5 mm) or less (edge-to-edge)

UW-20 TUBE-TO-TUBESHEET WELDS

UW-20.1 Scope. These rules provide a basis for establishing weld sizes and allowable joint loads for full strength and partial strength tube-to-tubesheet welds.

UW-20.2 Definitions

UW-20.2(a) Full Strength Weld. A full strength tubeto- tubesheet weld is one in which the design strength is equal to or greater than the axial tube strength, Ft. When the weld in a tube-to-tubesheet joint meets the requirements of UW-20.4, it is a full strength weld and the joint does not require qualification by shear load testing. Such a weld also provides tube joint leak tightness.UW-20.2(b) Partial Strength Weld. A partial strength weld is one in which the design strength is based on the mechanical and thermal axial tube loads (in either direction)

that are determined from the actual design conditions. The maximum allowable axial load of this weld may be determined in accordance with UW-20.5, Appendix A, or

UW-18(d). When the weld in a tube-to-tubesheet joint meets the requirements of UW-20.5 or UW-18(d), it is a partial strength weld and the joint does not require qualification

by shear load testing. Such a weld also provides tube joint leak tightness.UW-20.2(c) Seal Weld. A tube-to-tubesheet seal weld is one used to supplement an expanded tube joint to ensure leak tightness. Its size has not been determined based on

axial tube loading.

UW-20.3 Nomenclature. The symbols described below are used for the design of tube-to-tubesheet welds. ac = length of the combined weld legs measured parallel to the longitudinal axis of the tube at its outside diameter

af = fillet weld leg

ag= groove weld leg

ar = minimum required length of the weld leg(s) under consideration

do = tube outside diameter

Fd = design strength, but not greater than Ftfd = ratio of the design strength to the tube strength

= 1.0 for full strength welds

= Fd /Ft for partial strength welds

Ff = fillet weld strength, but not greater than Ft = 0.55af (do + 0.67af) Swff = ratio of the fillet weld strength to the design strength

= 1 Fg / (fd Ft)

Fg = groove weld strength, but not greater than Ft= 0.85ag (do + 0.67ag) SwFt = axial tube strength

= t (do t) Safw = weld strength factor

= Sa /SwLmax = maximum allowable axial load in either direction on the tube-to-tubesheet joint

S = allowable stress value as given in the applicable part of Section II, Part D

Sa = allowable stress in tube (see S, above)

St = allowable stress of the material to which the tube is welded (see S, above)

Sw = allowable stress in weld (lesser of Sa or St, above)

t = nominal tube thicknessNOTE: For a welded tube or pipe, use the allowable stress for the equivalent seamless product. When the allowable stress for the equivalent seamless product is not available, divide the allowable stress of the welded product by 0.85.

UW-20.4 Full Strength Welds. Full strength welds shown in Fig. UW-20.1 shall conform to the following requirements:

UW-20.4(a) The size of a full strength weld shall be determined in accordance with UW-20.6.

UW-20.4(b) The maximum allowable axial load in either direction on a tube-to-tubesheet joint with a full strength weld shall be determined as follows:

UW-20.4(b)(1) For loads due to pressure-induced axial forces, Lmax = Ft.

UW-20.4(b)(2) For loads due to thermally induced or pressure plus thermally induced axial forces:

UW-20.4(b)(2)(a) Lmax = Ft for welded only tube to- tubesheet joints, where the thickness through the weld throat is less than the nominal tube thickness t;

UW-20.4(b)(2)(b) Lmax= 2Ft for all other welded tube-to-tubesheet joints.

UW-20.5 Partial Strength Welds. Partial strength welds shown in Fig. UW-20.1 shall conform to the following requirements:

UW-20.5(a) The size of a partial strength weld shall be determined in accordance UW-20.6.

UW-20.5(b) The maximum allowable axial load in either direction on a tube-to-tubesheet joint with a partial strength weld shall be determined as follows:

UW-20.5(b)(1) For loads due to pressure-induced axial forces, LmaxpFf + Fg, but not greater than Ft.

UW-20.5(b)(2) For loads due to thermally induced or pressure plus thermally induced axial forces:

UW-20.5(b)(2)(a) LmaxpFf + Fg, but not greater than Ft, for welded only tube-to-tubesheet joints, where the thickness through the weld throat is less than the nominal

tube thickness t;

UW-20.5(b)(2)(b) Lmaxp2(Ff + Fg), but not greater than 2Ft, for all other welded tube-to-tubesheet joints.UW-20.6 Weld Size Design Formulas. The size of tube-to-tubesheet strength welds shown in Fig. UW-20.1 shall conform to the following requirements:

UW-20.6(a) For fillet welds shown in sketch (a),

ar p __0.75do_2 + 2.73t_do t_fwfd 0.75do

UW-20.6(a)(1) For full strength welds, af shall not be less than the greater of ar or t.

UW-20.6(a)(2) For partial strength welds, af shall not be less than ar.

UW-20.6(b) For groove welds shown in sketch (b),

ar p __0.75do_2 + 1.76t_do t_fwfd 0.75do

UW-20.6(b)(1) For full strength welds, ag shall not be less than the greater of ar or t.

UW-20.6(b)(2) For partial strength welds, ag shall not be less than ar.

UW-20.6(c) For combined groove and fillet welds shown in sketch (c), where af is equal to ag,

ar p 2___0.75do_2 + 1.07t_do t_fwfd 0.75do_

UW-20.6(c)(1) For full strength welds, ac shall not be less than the greater of ar or t.

UW-20.6(c)(2) For partial strength welds, ac shall not be less than ar.

Calculate af and ag: afpac/2 and agpac/2.

UW-20.6(d) For combined groove and fillet welds shown in sketch (d), where af is not equal to ag, ar shall be determined as follows: Choose ag. Calculate ar:

ar p __0.75do_2 + 2.73t_do t_fwfdff 0.75do

UW-20.6(d)(1) For full strength welds, ac shall not be less than the greater of (ar + ag) or t.

UW-20.6(d)(2) For partial strength welds, ac shall not be less than (ar + ag).

Calculate af: afpac ag.