Update app.py

app.py

@@ -1,12 +1,20 @@
 """
-Tubesheet Thickness Calculator (ASME VIII-1 preliminary)
+Tubesheet Thickness Calculator — ASME (with optional TEMA mode)
 Single-file Streamlit app.
 
-Updated:
- - removed the "minimum manufacturing thickness" input and all uses/display of it.
- - kept BWG (Birmingham Wire Gauge) selection for tube wall thickness with a manual override.
- - kept small-imperial-fraction support and previous logic.
-Note: The tool is preliminary — verify values (material allowable stresses, BWG table, allowances) before final design.
+Features:
+ - Shows allowable stress in the same units selected (MPa for SI, psi for Imperial).
+ - Sketch draws the actual tube centers inside the tubesheet circle using the chosen pitch and layout (square/triangular).
+ - Option for tube-side passes (affects reporting only — user should input appropriate tube-side pressure per pass if needed).
+ - Calculation follows ASME-style flat-plate bending approximation; TEMA option available as illustrative.
+ - BWG selection and manual thickness entry retained.
+ - Minimum manufacturing thickness removed per request.
+
+Notes:
+ - Bundled material allowable stresses are illustrative. Verify with ASME Section II for production.
+ - TEMA uses illustrative modifiers — consult TEMA documentation for strict compliance.
+Author: ChatGPT
+Updated: 2025-09-07
 """
 
 import streamlit as st
@@ -22,7 +30,7 @@ st.title("Tubesheet Thickness Calculator — ASME VIII-1 (Preliminary)")
 
 # -----------------------
 # Bundled (example) material table (sample values)
-# NOTE: These are illustrative. Replace with verified ASME Section II data for production use.
+# NOTE: illustrative only — replace with ASME Section II data for production
 MATERIAL_LOOKUP = {
     "SA-516 Gr 70": [
         {"temperature_C": 20,  "allowable_MPa": 138},
@@ -113,8 +121,6 @@ def interpolate_allowable(material, temp_C):
 
 # -----------------------
 # BWG table (typical reference values in inches)
-# NOTE: These are typical/approximate gauge-to-thickness values used for reference.
-# Validate against manufacturer data for critical designs.
 BWG_TO_INCH = {
     "BWG 7":   0.180,
     "BWG 8":   0.165,
@@ -142,7 +148,6 @@ BWG_TO_INCH = {
 
 # -----------------------
 # Sidebar — Inputs
-# -----------------------
 with st.sidebar:
     st.header("Inputs")
     project_name = st.text_input("Project name", value="Tubesheet Calculation")
@@ -166,18 +171,20 @@ with st.sidebar:
 
     effective_radius_override = st.checkbox("Override effective calculation radius (optional)")
     if effective_radius_override:
-        eff_radius = st.number_input(f"Effective radius ({u_len})",
-                                     min_value=1.0 if use_SI else 0.01,
-                                     value=(OD_ts/2.0),
-                                     step=1.0 if not use_SI else 0.01,
-                                     format="%.3f")
+        eff_radius = st.number_input(
+            f"Effective radius ({u_len})",
+            min_value=1.0 if use_SI else 0.01,
+            value=(OD_ts/2.0),
+            step=1.0 if not use_SI else 0.01,
+            format="%.3f"
+        )
     else:
         eff_radius = None
 
     st.subheader("Tube field")
     N_tubes = st.number_input("Number of tubes (N)", min_value=1, value=100, step=1)
 
-    # Allow small tube ODs: set min depending on units. e.g., allow 0.5 mm or 1/64 in
+    # Allow small tube ODs: set min depending on units.
     if use_SI:
         tube_od_min = 0.5   # mm
         tube_od_default = 25.4  # mm
@@ -201,19 +208,16 @@ with st.sidebar:
     selected_bwg = None
     t_tube = None
     if thickness_input_mode == "Select BWG gauge":
-        # show BWG options; display thickness in chosen units
         bwg_options = list(BWG_TO_INCH.keys())
-        selected_bwg = st.selectbox("BWG gauge", options=bwg_options, index=12)  # default to some mid gauge
-        # convert to selected units:
+        selected_bwg = st.selectbox("BWG gauge", options=bwg_options, index=12)
         thickness_inch = BWG_TO_INCH[selected_bwg]
         if use_SI:
             t_tube = inchtomm(thickness_inch)
-            st.write(f"Selected {selected_bwg} → wall thickness = {t_tube:.3f} mm (converted from {thickness_inch:.4f} in)")
+            st.write(f"Selected {selected_bwg} → wall thickness = {t_tube:.3f} mm (from {thickness_inch:.4f} in)")
         else:
             t_tube = thickness_inch
             st.write(f"Selected {selected_bwg} → wall thickness = {t_tube:.4f} in")
     else:
-        # manual entry; allow fine fractions for imperial
         if use_SI:
             t_tube_min = 0.1
             t_tube_default = 1.0
@@ -233,7 +237,7 @@ with st.sidebar:
 
     layout = st.selectbox("Tube pitch layout", options=["Triangular", "Square"])
 
-    # compute default pitch based on OD_tube; user can edit
+    # default pitch based on OD_tube; user can edit
     default_pitch = (OD_tube * 1.25) if (OD_tube is not None) else (25.4 * 1.25 if use_SI else 1.0 * 1.25)
     pitch = st.number_input(f"Tube pitch ({u_len})",
                              min_value=max(OD_tube * 1.0, tube_od_min),
@@ -242,7 +246,6 @@ with st.sidebar:
                              format=tube_od_format)
 
     st.subheader("Pressure & Temperature")
-    # default pressures
     if use_SI:
         P_shell = st.number_input(f"Design shell-side pressure ({u_press})", value=3.0, step=0.1)
         P_tube = st.number_input(f"Design tube-side pressure ({u_press})", value=1.0, step=0.1)
@@ -258,7 +261,7 @@ with st.sidebar:
     material_list = ["SA-516 Gr 70", "SA-240 Type 304", "SA-240 Type 316", "SA-105", "SA-36", "SA-387 Grade 11", "Other / Manual"]
     material = st.selectbox("Tubesheet material (ASME II examples)", options=material_list)
 
-    # Determine default usable temperature for lookup
+    # Determine default usable temperature for lookup (°C)
     if use_SI:
         T_shell_C = float(T_shell)
         T_tube_C = float(T_tube)
@@ -273,16 +276,24 @@ with st.sidebar:
 
     st.write("Allowable stress lookup (ASME Sec II - example table)")
     if S_allowable_auto is not None:
-        st.write(f"Auto lookup allowed stress: **{S_allowable_auto:.1f} MPa** at {use_temp_for_lookup:.1f} °C (interpolated)")
+        if use_SI:
+            st.write(f"Auto lookup allowed stress: **{S_allowable_auto:.1f} MPa** at {use_temp_for_lookup:.1f} °C (interpolated)")
+        else:
+            st.write(f"Auto lookup allowed stress: **{mpato_psi(S_allowable_auto):.1f} psi** at {use_temp_for_lookup:.1f} °C (interpolated)")
     else:
         st.write("No auto-lookup available for selected material & temperature in bundled table.")
 
-    S_override = st.checkbox("Manual override allowable stress (MPa)")
+    S_override = st.checkbox("Manual override allowable stress")
+    # prepare both vars so later code can rely on them
+    S_allowable_manual = None
+    S_allowable_manual_psi = None
     if S_override:
-        default_S = S_allowable_auto if S_allowable_auto is not None else 100.0
-        S_allowable_manual = st.number_input("S_allowable (MPa)", min_value=1.0, value=float(default_S), step=1.0)
-    else:
-        S_allowable_manual = None
+        if use_SI:
+            default_S = S_allowable_auto if S_allowable_auto is not None else 100.0
+            S_allowable_manual = st.number_input("S_allowable (MPa)", min_value=1.0, value=float(default_S), step=1.0)
+        else:
+            default_S_psi = mpato_psi(S_allowable_auto) if S_allowable_auto is not None else mpato_psi(100.0)
+            S_allowable_manual_psi = st.number_input("S_allowable (psi)", min_value=1.0, value=float(default_S_psi), step=1.0)
 
     st.subheader("Allowances & Options")
     if use_SI:
@@ -294,12 +305,75 @@ with st.sidebar:
 
     edge_condition = st.selectbox("Edge condition (plate support)", options=["Clamped (conservative)", "Simply supported (less conservative)"])
     safety_factor = st.number_input("Conservative multiplier (SF) applied to allowable stress", min_value=0.5, max_value=3.0, value=1.0, step=0.05)
+
+    st.subheader("Calculation basis")
+    calc_basis = st.selectbox("Calculation method", options=["ASME (default)", "TEMA (illustrative)"])
+
+    st.subheader("Extra options")
+    passes = st.number_input("Number of tube-side passes", min_value=1, value=1, step=1)
+
     show_detail = st.checkbox("Show detailed calculations (expandable)", value=False)
     compute = st.button("Compute")
 
 # -----------------------
-# Calculation logic
+# Helper: generate tube grid (square or triangular) inside a circle
+def generate_tube_centers(radius_mm, pitch_mm, layout="Triangular", tube_OD_mm=0.0, max_count=None):
+    """
+    radius_mm: circle radius
+    pitch_mm: center-to-center pitch
+    layout: 'Triangular' or 'Square'
+    tube_OD_mm: used to ensure tube edges don't cross the circle (center must be <= radius - tube_OD/2)
+    returns: list of (x_mm, y_mm)
+    """
+    centers = []
+    R = radius_mm
+    if pitch_mm <= 0:
+        return centers
+
+    if layout == "Square":
+        xs = np.arange(-R, R + 1e-8, pitch_mm)
+        ys = np.arange(-R, R + 1e-8, pitch_mm)
+        for x in xs:
+            for y in ys:
+                if x**2 + y**2 <= (R - tube_OD_mm/2.0)**2:
+                    centers.append((x, y))
+                    if max_count and len(centers) >= max_count:
+                        return centers
+    else:
+        vert = pitch_mm * math.sqrt(3)/2.0
+        # construct rows symmetric about y=0
+        # start from center row and go outwards to cover -R..R
+        row_offsets = []
+        y_center = 0.0
+        row_offsets.append(y_center)
+        step = vert
+        n = 1
+        while True:
+            y_up = n * step
+            y_down = -n * step
+            if abs(y_up) <= R or abs(y_down) <= R:
+                if abs(y_up) <= R:
+                    row_offsets.append(y_up)
+                if abs(y_down) <= R:
+                    row_offsets.append(y_down)
+                n += 1
+            else:
+                break
+        row_offsets = sorted(set(row_offsets))
+        for idx, y in enumerate(row_offsets):
+            if idx % 2 == 0:
+                xs = np.arange(-R, R + 1e-8, pitch_mm)
+            else:
+                xs = np.arange(-R + pitch_mm/2.0, R + 1e-8, pitch_mm)
+            for x in xs:
+                if x**2 + y**2 <= (R - tube_OD_mm/2.0)**2:
+                    centers.append((x, y))
+                    if max_count and len(centers) >= max_count:
+                        return centers
+    return centers
+
 # -----------------------
+# Calculation logic
 def compute_all():
     # Unit conversions into consistent internal units:
     # lengths in mm, pressure in MPa, stresses in MPa
@@ -309,8 +383,7 @@ def compute_all():
         pitch_mm = float(pitch)
         CA_mm = float(CA)
         machining_mm = float(machining)
-        # t_tube currently in mm if user selected BWG (converted) or manual in mm
-        t_tube_mm_input = float(t_tube) if use_SI else inchtomm(float(t_tube))  # safe fallback
+        t_tube_mm_input = float(t_tube)
         P_shell_MPa = bartompa(float(P_shell))
         P_tube_MPa = bartompa(float(P_tube))
         T_shellC = float(T_shell)
@@ -321,7 +394,6 @@ def compute_all():
         pitch_mm = inchtomm(float(pitch))
         CA_mm = inchtomm(float(CA))
         machining_mm = inchtomm(float(machining))
-        # t_tube currently in inches if user selected BWG or manual imperial entry
         t_tube_mm_input = inchtomm(float(t_tube))
         P_shell_MPa = psito_mpa(float(P_shell))
         P_tube_MPa = psito_mpa(float(P_tube))
@@ -342,23 +414,34 @@ def compute_all():
     q = deltaP_MPa  # MPa (N/mm^2) as a uniform load approximation
 
     # allowable stress selection
-    if S_override and S_allowable_manual is not None:
-        S_allow_MPa = float(S_allowable_manual)
+    if S_override:
+        if use_SI:
+            S_allow_MPa = float(S_allowable_manual)
+        else:
+            # ensure psi->MPa conversion
+            S_allow_MPa = psito_mpa(float(S_allowable_manual_psi))
         source_S = "Manual override"
     else:
         S_allow_MPa = S_allowable_auto if S_allowable_auto is not None else None
         source_S = "Auto lookup (interpolated)" if S_allowable_auto is not None else "None available"
 
-    # if S not available, set to a conservative default and warn
+    # fallback if none available
     if S_allow_MPa is None:
         S_allow_MPa = 100.0
         source_S = "Default used (no lookup) - user must verify"
 
-    # choose k based on edge condition
-    if edge_condition.startswith("Clamped"):
-        k = 0.308
+    # choose k based on edge condition and calculation basis
+    if calc_basis.startswith("ASME"):
+        if edge_condition.startswith("Clamped"):
+            k = 0.308
+        else:
+            k = 0.375
     else:
-        k = 0.375
+        # TEMA illustrative modifiers (verify with TEMA docs)
+        if edge_condition.startswith("Clamped"):
+            k = 0.27
+        else:
+            k = 0.33
 
     SF = float(safety_factor)
 
@@ -371,10 +454,13 @@ def compute_all():
     else:
         t_req_mm = math.sqrt(max(numerator / denom, 0.0))
 
+    # determine tube centers using pitch and layout (limit to user N_tubes)
+    centers = generate_tube_centers(radius_mm=a_mm - 1e-8, pitch_mm=pitch_mm, layout=layout, tube_OD_mm=OD_tube_mm, max_count=N_tubes)
+    actual_N = len(centers)
     # hole area and percent removed
-    hole_area_mm2 = N_tubes * math.pi * (OD_tube_mm / 2.0) ** 2
+    hole_area_mm2 = actual_N * math.pi * (OD_tube_mm / 2.0) ** 2
     plate_area_mm2 = math.pi * (a_mm ** 2)
-    hole_removed_pct = (hole_area_mm2 / plate_area_mm2) * 100.0
+    hole_removed_pct = (hole_area_mm2 / plate_area_mm2) * 100.0 if plate_area_mm2 > 0 else 0.0
 
     # local bearing / ligament check (simple)
     net_area_mm2 = max(plate_area_mm2 - hole_area_mm2, 1.0)
@@ -392,12 +478,16 @@ def compute_all():
             "t_final_unrounded_mm": t_final_unrounded_mm,
             "t_final_rounded_mm": t_final_rounded_mm,
             "S_allow_MPa": S_allow_MPa,
+            "S_allow_display": f"{S_allow_MPa:.2f} MPa",
             "deltaP_MPa": deltaP_MPa,
+            "deltaP_display": f"{deltaP_MPa:.4f} MPa",
             "hole_removed_pct": hole_removed_pct,
             "avg_membrane_stress_approx_MPa": avg_membrane_stress_approx,
+            "avg_membrane_stress_approx_display": f"{avg_membrane_stress_approx:.3f} MPa",
             "bearing_flag": bearing_flag,
             "a_mm": a_mm,
             "t_tube_mm_input": t_tube_mm_input,
+            "actual_N": actual_N,
             "source_S": source_S
         }
     else:
@@ -406,15 +496,16 @@ def compute_all():
             "t_final_unrounded_in": mmtoinch(t_final_unrounded_mm),
             "t_final_rounded_in": round_up_standard_in(mmtoinch(t_final_rounded_mm)),
             "S_allow_MPa": S_allow_MPa,
-            "S_allow_psi": mpato_psi(S_allow_MPa),
+            "S_allow_display": f"{mpato_psi(S_allow_MPa):.1f} psi",
             "deltaP_MPa": deltaP_MPa,
-            "deltaP_psi": mpato_psi(deltaP_MPa),
+            "deltaP_display": f"{mpato_psi(deltaP_MPa):.2f} psi",
             "hole_removed_pct": hole_removed_pct,
             "avg_membrane_stress_approx_MPa": avg_membrane_stress_approx,
-            "avg_membrane_stress_approx_psi": mpato_psi(avg_membrane_stress_approx),
+            "avg_membrane_stress_approx_display": f"{mpato_psi(avg_membrane_stress_approx):.2f} psi",
             "bearing_flag": bearing_flag,
             "a_in": mmtoinch(a_mm),
             "t_tube_in_input": mmtoinch(t_tube_mm_input),
+            "actual_N": actual_N,
             "source_S": source_S
         }
 
@@ -425,7 +516,7 @@ def compute_all():
     log_lines.append("---- Units (internal calculations): lengths=mm, pressures=MPa, stress=MPa ----")
     log_lines.append(f"Selected units: {units}")
     log_lines.append(f"OD_ts = {OD_ts} {u_len} -> a = {a_mm:.2f} mm")
-    log_lines.append(f"N_tubes = {N_tubes}, OD_tube = {OD_tube} {u_len} -> OD_tube_mm = {OD_tube_mm:.6f} mm")
+    log_lines.append(f"Requested N_tubes = {N_tubes}, Actual placed = {actual_N}, OD_tube = {OD_tube} {u_len} -> OD_tube_mm = {OD_tube_mm:.6f} mm")
     log_lines.append(f"Tube wall thickness input mode = {thickness_input_mode}")
     if thickness_input_mode == "Select BWG":
         log_lines.append(f"Selected BWG = {selected_bwg}, t_tube = {t_tube_mm_input:.4f} mm")
@@ -434,7 +525,7 @@ def compute_all():
     log_lines.append(f"Pressures: P_shell = {P_shell} {u_press} ({P_shell_MPa:.6f} MPa), P_tube = {P_tube} {u_press} ({P_tube_MPa:.6f} MPa)")
     log_lines.append(f"ΔP (governing) = |P_shell - P_tube| = {deltaP_MPa:.6f} MPa")
     log_lines.append(f"Material: {material} (S source: {source_S}), S_used = {S_allow_MPa:.3f} MPa")
-    log_lines.append(f"Edge condition k = {k}, safety multiplier SF = {SF}")
+    log_lines.append(f"Calculation basis: {calc_basis}, Edge condition k = {k}, safety multiplier SF = {SF}")
     log_lines.append(f"Plate bending formula used: t_req = sqrt( (q * a^2) / (k * S * SF) )")
     log_lines.append(f"Substitution: q={q:.6f} MPa, a={a_mm:.3f} mm, k={k}, S={S_allow_MPa:.3f} MPa, SF={SF}")
     log_lines.append(f"Computed t_req = {t_req_mm:.3f} mm")
@@ -450,25 +541,32 @@ def compute_all():
     # produce summary table (pandas)
     summary = []
     summary.append(["Tubesheet OD", f"{OD_ts} {u_len}"])
-    summary.append(["Number of tubes", f"{N_tubes}"])
+    summary.append(["Number of tubes (requested)", f"{N_tubes}"])
+    summary.append(["Number of tubes (placed)", f"{actual_N}"])
     summary.append(["Tube OD", f"{OD_tube} {u_len}"])
     if use_SI:
         summary.append(["Tube wall thickness (input)", f"{t_tube_mm_input:.3f} mm"])
     else:
         summary.append(["Tube wall thickness (input)", f"{mmtoinch(t_tube_mm_input):.4f} in"])
     summary.append(["Pitch", f"{pitch} {u_len}"])
+    summary.append(["Layout", f"{layout}"])
     summary.append(["Material", material])
-    summary.append(["S_used (MPa)", f"{S_allow_MPa:.3f}"])
-    summary.append(["ΔP", f"{deltaP_MPa:.6f} MPa ({mpato_psi(deltaP_MPa):.2f} psi)"])
+    summary.append(["S_used", results['S_allow_display']])
+    summary.append(["ΔP", results['deltaP_display']])
     if use_SI:
-        summary.append(["t_req (mm)", f"{t_req_mm:.3f}"])
-        summary.append(["t_final_unrounded (mm)", f"{t_final_unrounded_mm:.3f}"])
-        summary.append(["t_final_rounded (mm)", f"{t_final_rounded_mm:.3f}"])
+        summary.append(["t_req (mm)", f"{results['t_req_mm']:.3f}"])
+        summary.append(["t_final_unrounded (mm)", f"{results['t_final_unrounded_mm']:.3f}"])
+        summary.append(["t_final_rounded (mm)", f"{results['t_final_rounded_mm']:.3f}"])
     else:
-        summary.append(["t_req (in)", f"{mmtoinch(t_req_mm):.4f}"])
-        summary.append(["t_final_unrounded (in)", f"{mmtoinch(t_final_unrounded_mm):.4f}"])
-        summary.append(["t_final_rounded (in)", f"{round_up_standard_in(mmtoinch(t_final_rounded_mm)):.4f}"])
+        summary.append(["t_req (in)", f"{results['t_req_in']:.4f}"])
+        summary.append(["t_final_unrounded (in)", f"{results['t_final_unrounded_in']:.4f}"])
+        summary.append(["t_final_rounded (in)", f"{results['t_final_rounded_in']:.4f}"])
     summary.append(["Hole removed (%)", f"{hole_removed_pct:.2f}%"])
+    if use_SI:
+        summary.append(["Approx avg membrane stress", f"{results['avg_membrane_stress_approx_MPa']:.3f} MPa ({mpato_psi(results['avg_membrane_stress_approx_MPa']):.2f} psi)"])
+    else:
+        summary.append(["Approx avg membrane stress", f"{results['avg_membrane_stress_approx_display']}"])
+    summary.append(["Tube-side passes", f"{passes}"])
     summary_df = pd.DataFrame(summary, columns=["Parameter", "Value"])
 
     # CSV export
@@ -476,13 +574,16 @@ def compute_all():
     summary_df.to_csv(csv_buffer, index=False)
     csv_data = csv_buffer.getvalue().encode("utf-8")
 
-    return results, log_text, summary_df, csv_data
+    # Convert centers into normalized plot coordinates for schematic: scale by a_mm (radius)
+    # Plot uses coordinates in range [-1,1]
+    plot_centers = [(x / a_mm, y / a_mm) for (x, y) in centers]
+
+    return results, log_text, summary_df, csv_data, plot_centers, OD_tube_mm, a_mm
 
 # -----------------------
 # Run compute and display results
-# -----------------------
 if compute:
-    results, log_text, summary_df, csv_bytes = compute_all()
+    results, log_text, summary_df, csv_bytes, plot_centers, OD_tube_mm, a_mm = compute_all()
 
     # Show KPI cards
     st.subheader("Results")
@@ -497,34 +598,37 @@ if compute:
         c1.metric("Required thickness (t_req)", f"{results['t_req_in']:.4f} in")
         c2.metric("Final thickness (unrounded)", f"{results['t_final_unrounded_in']:.4f} in")
         c3.metric("Final thickness (rounded)", f"{results['t_final_rounded_in']:.4f} in")
-        c4.metric("ΔP", f"{results['deltaP_psi']:.2f} psi")
+        c4.metric("ΔP", results['deltaP_display'])
 
     # Summary table and schematic
     left, right = st.columns([2,3])
     with left:
         st.markdown("**Summary table**")
         st.dataframe(summary_df, use_container_width=True)
-
         st.download_button("Download summary CSV", data=csv_bytes, file_name="tubesheet_summary.csv", mime="text/csv")
 
     with right:
-        st.markdown("**Schematic (not to scale)**")
-        # create a simple schematic: circle for tubesheet, points for tube field (visual)
+        st.markdown("**Schematic (to scale in layout) — normalized to tubesheet radius**")
         fig = go.Figure()
+        # outer circle (radius = 1 normalized)
         theta = np.linspace(0, 2*np.pi, 200)
         fig.add_trace(go.Scatter(x=np.cos(theta), y=np.sin(theta), mode="lines", name="Tubesheet OD",
-                                 line=dict(color="RoyalBlue")))
-        n_mark = min(300, int(N_tubes))
-        xs = []
-        ys = []
-        r = 0.85
-        for i in range(n_mark):
-            ang = 2*np.pi*i / n_mark
-            xs.append(0.5 * r * np.cos(ang))
-            ys.append(0.5 * r * np.sin(ang))
-        fig.add_trace(go.Scatter(x=xs, y=ys, mode="markers", marker=dict(size=4, color="DarkOrange"), name="Tube holes"))
-        fig.update_layout(width=600, height=600, margin=dict(l=10,r=10,t=10,b=10), showlegend=False,
-                          xaxis=dict(visible=False), yaxis=dict(visible=False), title_text="Tubesheet schematic (not to scale)")
+                                 line=dict(width=2, color="RoyalBlue")))
+        # tubes as markers; scale marker size approx proportional to OD_tube_mm / a_mm
+        xs = [c[0] for c in plot_centers]
+        ys = [c[1] for c in plot_centers]
+        # compute pixel-like marker size but keep within reasonable bounds
+        if a_mm > 0:
+            # fraction of normalized radius occupied by tube radius
+            frac = (OD_tube_mm / 2.0) / a_mm
+            # convert fraction to marker size (empirical scaling)
+            marker_size = max(4, min(40, frac * 800))
+        else:
+            marker_size = 6
+        fig.add_trace(go.Scatter(x=xs, y=ys, mode="markers", marker=dict(size=marker_size), name="Tube holes"))
+        fig.update_layout(width=800, height=800, margin=dict(l=10,r=10,t=30,b=10), showlegend=False,
+                          xaxis=dict(visible=False, range=[-1.05,1.05]), yaxis=dict(visible=False, range=[-1.05,1.05]),
+                          title_text="Tubesheet layout (normalized to radius = 1)")
         st.plotly_chart(fig, use_container_width=True)
 
     # Calculation log
@@ -534,9 +638,10 @@ if compute:
 
     # Warnings and notes
     st.markdown("### Notes & Warnings")
-    st.markdown("- This is a **preliminary** sizing tool using a simplified flat-plate approximation (clamped or simply supported).")
+    st.markdown("- This is a **preliminary** sizing tool using a simplified flat-plate approximation (ASME-like plate bending formula).")
     st.markdown("- The bundled material table is illustrative. **Verify allowable stresses with ASME Section II** for your material and temperature.")
-    st.markdown("- The BWG → thickness mapping is provided as a common reference. **Confirm exact tube wall thickness with manufacturer or datasheet before final design.**")
+    st.markdown("- The BWG → thickness mapping is provided as a reference. **Confirm exact tube wall thickness with manufacturer/datasheet before final design.**")
+    st.markdown("- TEMA option uses illustrative modifiers only — consult TEMA standards if you choose that path.")
     st.markdown("- Final design must be verified and stamped by a qualified engineer as per ASME Section VIII Division 1.")
 
 else:
@@ -544,12 +649,11 @@ else:
 
 # -----------------------
 # Presets (quick-load examples)
-# -----------------------
 st.sidebar.markdown("---")
 st.sidebar.markdown("### Presets")
 if st.sidebar.button("Example 1 (SI)"):
-    st.write("Preset example: OD 1000 mm, 100 tubes, tube OD 25.4 mm, P_shell=3 bar, P_tube=1 bar.")
+    st.info("Preset example: OD 1000 mm, ~100 tubes, tube OD 25.4 mm, P_shell=3 bar, P_tube=1 bar — set values manually or copy/paste into fields.")
 if st.sidebar.button("Example 2 (Imperial)"):
-    st.write("Preset example: OD 40 in, 200 tubes, tube OD 0.75 in, P_shell=50 psi, P_tube=14.7 psi")
+    st.info("Preset example: OD 40 in, ~200 tubes, tube OD 0.75 in, P_shell=50 psi, P_tube=14.7 psi — set values manually or copy/paste into fields.")
 
 # End of app